home Botany book Structural features of membrane proteins. Membrane proteins, their structure, properties and features. Translocase mechanism of action

Structural features of membrane proteins. Membrane proteins, their structure, properties and features. Translocase mechanism of action

Lipids in the composition of membranes are assigned, first of all, structural properties - they create a bilayer, or matrix, in which the active components of the membrane - proteins - are located. It is proteins that give various membranes their uniqueness and provide specific properties. Numerous membrane proteins perform the following main functions: they determine the transfer of substances through membranes (transport functions), carry out catalysis, provide processes for photo- and oxidative phosphorylation, DNA replication, translation and modification of proteins, signal reception and transmission nerve impulse and etc.

It is customary to divide membrane proteins into 2 groups: integral(internal) and peripheral(external). The criterion for such a separation is the degree of strength of protein binding to the membrane and, accordingly, the degree of severity of processing required to extract the protein from the membrane. Thus, peripheral proteins can be released into solution already when membranes are washed with buffer mixtures with low ionic strength, low pH values in the presence of chelating agents, for example, ethylenediaminetetraacetate (EDTA), which bind divalent cations. Peripheral proteins are released from membranes under such mild conditions, since they are associated with lipid heads or with other membrane proteins by weak electrostatic interactions, or by hydrophobic interactions with lipid tails. On the contrary, integral proteins are amphiphilic molecules, have large hydrophobic regions on their surface and are located inside the membrane; therefore, to extract them, it is necessary to destroy the bilayer. For these purposes, detergents or organic solvents are most often used. The ways of attaching proteins to the membrane are quite diverse (Fig. 4.8).

Transport proteins. The lipid bilayer is an impenetrable barrier for most water-soluble molecules and ions, and their transport through biomembranes depends on the activity of transport proteins. There are two main types of these proteins: channels(pores) and carriers. Channels are membrane-crossing tunnels in which the binding sites of the transported substances are available on both surfaces of the membrane at the same time. Channels do not undergo any conformational changes during the transport of substances; their conformation changes only when opening and closing. Carriers, on the contrary, change their conformation during the transfer of substances across the membrane. Moreover, at each specific point in time, the binding site of the transferred substance in the carrier is available only on one surface of the membrane.

Channels, in turn, can be divided into two main groups: voltage-dependent and chemically regulated. An example of a voltage-dependent channel is the Na + channel, its operation is regulated by changing the voltage electric field. In other words, these channels open and close in response to a change transmembrane potential. Chemically regulated channels

open and close in response to the binding of specific chemical agents. For example, when a neurotransmitter binds to the nicotinic acetylcholine receptor, it changes into an open conformation and allows monovalent cations to pass through (subsection 4.7 of this chapter). The terms "pore" and "channel" are usually interchangeable, but sometimes they are understood as non-selective structures that distinguish substances mainly by size and allow all sufficiently small molecules to pass through. Channels are often referred to as ion channels. The rate of transport through an open channel reaches 10 6 - 10 8 ions per second.

Carriers can also be divided into 2 groups: passive and active. With the help of passive carriers, one type of substances is transported across the membrane. Passive carriers are involved in facilitated diffusion and only increase the flow of the substance, which is carried out along the electrochemical gradient (for example, the transfer of glucose through the membranes of erythrocytes). Active carriers transport substances across the membrane at the cost of energy. These transport proteins accumulate substances on one side of the membrane, carrying them against the electrochemical gradient. The speed of transport with the help of carriers depends very much on their type and ranges from 30 to 10 5 s -1 . Often, the terms "permease", "translocase" are used to refer to individual carriers, which can be considered synonymous with the term "carrier".

Enzymatic functions of membrane proteins. A wide variety of enzymes function in cell membranes. Some of them are localized in the membrane, finding there a suitable environment for the transformation of hydrophobic compounds, others, due to the participation of membranes, are located in them in strict order, catalyzing the successive stages of life. important processes, others need the assistance of lipids to stabilize their conformation and maintain activity. Enzymes were found in biomembranes - representatives of all known classes. They can penetrate the membrane through, be present in it in a dissolved form, or, being peripheral proteins, bind to membrane surfaces in response to some signal. The following characteristic types of membrane enzymes can be distinguished:

1) transmembrane enzymes that catalyze coupled reactions on opposite sides of the membrane. These enzymes have, as a rule, several active centers located on opposite sides of the membrane. Typical representatives of such enzymes are respiratory chain components or photosynthetic redox centers that catalyze redox processes associated with electron transport and the creation of ionic gradients on the membrane;

2) transmembrane enzymes involved in the transport of substances. Transport proteins that couple the transfer of a substance with ATP hydrolysis, for example, have a catalytic function;

3) enzymes that catalyze the conversion of membrane-bound substrates. These enzymes are involved in the metabolism of membrane components: phospholipids, glycolipids, steroids, etc.

4) enzymes involved in the transformation of water-soluble substrates. With the help of membranes, most often in the state attached to them, enzymes can concentrate in those areas of the membranes where the content of their substrates is greatest. For example, enzymes that hydrolyze proteins and starch attach to the membranes of intestinal microvilli, which increases the rate of degradation of these substrates.

Proteins of the cytoskeleton . The cytoskeleton is a complex network of protein fibers of various types and is present only in eukaryotic cells. The cytoskeleton provides mechanical support for the plasma membrane, can determine the shape of the cell, as well as the location of organelles and their movement during mitosis. With the participation of the cytoskeleton, such important processes for the cell as endo- and exocytosis, phagocytosis, and amoeboid movement are also carried out. Thus, the cytoskeleton is the dynamic framework of the cell and determines its mechanics.

The cytoskeleton is formed from three types of fibers:

1) microfilaments(diameter ~ 6 nm). They are filamentous organelles - polymers of the globular protein actin and other proteins associated with it;

2) intermediate filaments (diameter 8-10 nm). Formed by keratins and related proteins;

3) microtubules(diameter ~ 23 nm) - long tubular structures.

They consist of the globular protein tubulin, the subunits of which form a hollow cylinder. The length of microtubules can reach several micrometers in the cytoplasm of cells and several millimeters in the axons of nerves.

These structures of the cytoskeleton penetrate the cell in different directions and are closely associated with the membrane, attaching to it at some points. These sections of the membrane play an important role in intercellular contacts; with their help, cells can attach to the substrate. They also play an important role in the transmembrane distribution of lipids and proteins in membranes.

The future of medicine is personalized methods of selective influence on individual systems cells that are responsible for the development and course of a particular disease. The main class of therapeutic targets in this case are cell membrane proteins as structures responsible for providing direct signal transmission to the cell. Already today, almost half of the drugs affect cell membranes, and there will only be more of them in the future. This article is devoted to acquaintance with the biological role of membrane proteins.

Structure and function of the cell membrane

From school course many remember the structure of the structural unit of the body - the cell. A special place in the structure of a living cell is played by the plasmalemma (membrane), which separates the intracellular space from its environment. Thus, its main function is to create a barrier between the cellular content and the extracellular space. But this is not the only function of the plasmalemma. Other membrane functions associated primarily with membrane proteins include:

Protective (binding antigens and preventing their penetration into the cell).
Transport (ensuring the exchange of substances between the cell and the environment).
Signaling (built-in receptor protein complexes provide cell irritability and its response to various external influences).
Energy - the transformation of various forms of energy: mechanical (flagella and cilia), electrical (nerve impulse) and chemical (synthesis of adenosine triphosphoric acid molecules).
Contact (providing communication between cells with the help of desmosomes and plasmodesmata, as well as folds and outgrowths of the plasmolemma).

The structure of membranes

The cell membrane is a double layer of lipids. The bilayer is formed due to the presence in the lipid molecule of two parts with different properties - a hydrophilic and hydrophobic section. The outer layer of the membranes is formed by polar "heads" with hydrophilic properties, and the hydrophobic "tails" of lipids are turned inside the bilayer. In addition to lipids, the structure of membranes includes proteins. In 1972, American microbiologists S.D. Singer (S. Jonathan Singer) and G.L. Nicholson (Garth L. Nicolson) proposed a fluid-mosaic model of the membrane structure, according to which membrane proteins "float" in the lipid bilayer. This model was supplemented by the German biologist Kai Simons (1997) in terms of the formation of specific, denser regions with associated proteins (lipid rafts) that drift freely in the membrane bilayer.

Spatial structure of membrane proteins

In different cells, the ratio of lipids and proteins is different (from 25 to 75% of proteins in terms of dry weight), and they are unevenly located. According to the location of the proteins can be:

Integral (transmembrane) - built into the membrane. At the same time, they penetrate the membrane, sometimes repeatedly. Their extracellular regions often carry oligosaccharide chains, forming glycoprotein clusters.
Peripheral - located mainly on the inside of the membranes. Communication with membrane lipids is provided by reversible hydrogen bonds.
Anchored - predominantly located on the outside of the cell and the "anchor" holding them on the surface is a lipid molecule immersed in the bilayer.

Functionality and responsibilities

The biological role of membrane proteins is diverse and depends on their structure and location. Among them, receptor proteins, channel proteins (ionic and porins), transporters, motors, and structural protein clusters are distinguished. All types of membrane protein receptors, in response to any impact, change their spatial structure and form the response of the cell. For example, the insulin receptor regulates the entry of glucose into the cell, and rhodopsin in the sensitive cells of the organ of vision triggers a cascade of reactions that lead to the appearance of a nerve impulse. The role of membrane protein channels is to transport ions and maintain their difference between the internal and external environment. For example, sodium-potassium pumps ensure the exchange of the corresponding ions and substances. Porins - through proteins - are involved in the transfer of water molecules, transporters - in the transfer of certain substances against a concentration gradient. In bacteria and protozoa, the movement of flagella is provided by molecular protein motors. Structural membrane proteins support the membrane itself and ensure the interaction of other plasma membrane proteins.

Membrane proteins, protein membrane

The membrane is a dynamic and very active environment, and not an inert matrix for the proteins that are located and work in it. It significantly affects the work of membrane proteins, and lipid rafts, moving, form new associative bonds of protein molecules. Many proteins simply do not work without partners, and their intermolecular interaction is provided by the nature of the lipid layer of membranes, the structural organization of which, in turn, depends on structural proteins. Disturbances in this delicate mechanism of interaction and interdependence lead to dysfunction of membrane proteins and a variety of diseases, such as diabetes and malignant tumors.

Structural organization

Modern ideas about the structure and structure of membrane proteins are based on the fact that in the membrane peripheral part, most of them rarely consist of one, more often of several associated oligomerizing alpha helices. Moreover, it is this structure that is the key to the performance of the function. However, it is the classification of proteins according to the types of structures that can bring many more surprises. Of more than a hundred described proteins, the most studied membrane protein in terms of the type of oligomerization is glycophorin A (erythrocyte protein). For transmembrane proteins, the situation looks more complicated - only one protein has been described (the photosynthetic reaction center of bacteria - bacteriorhodopsin). Given the high molecular weight of membrane proteins (10-240 thousand daltons), molecular biologists wide field for research.

cell signaling systems

Among all proteins of the plasmalemma, a special place belongs to receptor proteins. It is they who regulate which signals enter the cell and which do not. In all multicellular and some bacteria, information is transmitted through special molecules (signal). Among these signaling agents, there are specially secreted cells), non-protein formations, and individual ions. The latter can be released when neighboring cells are damaged and trigger a cascade of reactions in the form of a pain syndrome, the main defense mechanism organism.

Targets for pharmacology

It is membrane proteins that are the main targets of pharmacology, since they are the points through which most signals pass. "Aim" medicinal product, to ensure its high selectivity - this is the main task when creating a pharmacological agent. Selective action only on a specific type or even subtype of the receptor is the effect on only one type of body cells. Such a selective effect can, for example, distinguish tumor cells from normal ones.

Medicines of the future

The properties and features of membrane proteins are already used today in the creation of new generation drugs. These technologies are based on the creation of modular pharmacological structures from several molecules or nanoparticles “cross-linked” with each other. The “targeting” part recognizes certain receptor proteins on the cell membrane (for example, those associated with the development of oncological diseases). To this part is added a membrane-destroying agent or a blocker in the processes of protein production in the cell. Developing apoptosis (the program of one's own death) or another mechanism of the cascade of intracellular transformations leads to the desired result of exposure to a pharmacological agent. As a result, we have a drug with a minimum of side effects. The first such cancer-fighting drugs are already in clinical trials and will soon become highly effective therapies.

Structural genomics

The modern science of protein molecules is increasingly moving towards information Technology. An extensive path of research - to study and describe everything that is possible, to store the data in computer databases and then look for ways to apply this knowledge - this is the goal of modern molecular biologists. Just fifteen years ago, the global human genome project started, and we already have a sequenced map of human genes. The second project, the purpose of which is to determine the spatial structure of all "key proteins", - structural genomics - is far from complete. The spatial structure has so far been determined only for 60,000 of more than five million human proteins. And while scientists have grown only luminous pigs and cold-resistant tomatoes with the salmon gene, structural genomics technologies remain a stage of scientific knowledge, the practical application of which will not be long in coming.

1 . structural proteins determine the structure of the membrane

2 . receptor- participate in the recognition and attachment of substances

3 .antigenic- determine the specifics of the membrane surface and its interaction with the environment

4 . enzymatic- catalysis of metabolic processes, changes in the surrounding substrate

5 . transport- formation of pores, transport of substances through the membrane, transport of electrons

Physico-chemical features of cell membranes

1. Selective (differential) permeability - the entry into the cell of a quantity and quality of substances adequate to its needs

q Thanks to this, an appropriate concentration of ions is created and maintained in the cell and osmotic phenomena are carried out)

q Some membranes allow only solvent molecules to pass through while retaining all solute molecules or ions – semipermeability membranes

2. The presence of a difference in electrical potentials on both sides of the membrane ( electric charge)

3. Is in a constant wave-like oscillatory motion

4. The ability to self-assembly after a destructive impact of a certain intensity - regeneration (reparation)

5. Membranes of different cell types differ significantly in chemical composition, content of protein, glycoproteins and lipids

There are two types of membranes: plasma (plasmolemma) and internal (they differ in chemical composition and properties)

End of work -

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Essence of life

Living matter qualitatively differs from non-living matter by its enormous complexity and high structural and functional orderliness. Living and non-living matter are similar in elementary chemical level te.. Chemical compounds cell substances.

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Mutation process and reserve of hereditary variability
In the gene pool of populations, a continuous mutation process occurs under the influence of mutagenic factors Recessive alleles mutate more often (encode less resistant to the action of mutagenic fa

Allele and genotype frequencies (population genetic structure)
The genetic structure of a population is the ratio of the frequencies of alleles (A and a) and genotypes (AA, Aa, aa) in the gene pool of the population Allele frequency

Cytoplasmic inheritance
There are data that are inexplicable from the point of view of chromosome theory heredity of A. Weisman and T. Morgan (i.e., exclusively nuclear localization of genes) The cytoplasm is involved in re

Plasmogenes of mitochondria
One myotochondria contains 4-5 circular DNA molecules about 15,000 base pairs long Contains genes for: - synthesis of t RNA, p RNA and ribosome proteins, some aero enzymes

Plasmids
Plasmids are very short, autonomously replicating circular fragments of the bacterial DNA molecule that provide non-chromosomal transmission of hereditary information.

Variability
Variability - common property all organisms acquire structural and functional differences from their ancestors.

Mutational variability
Mutations - qualitative or quantitative DNA of body cells, leading to changes in their genetic apparatus (genotype) Mutation theory of creation

Causes of Mutations
Mutagenic factors (mutagens) - substances and influences capable of inducing a mutational effect (any factors of the external and internal environment that can

Mutation frequency
· The frequency of mutation of individual genes varies widely and depends on the state of the organism and the stage of ontogeny (usually increases with age). On average, each gene mutates once every 40,000 years.

Gene mutations (point, true)
The reason is a change in the chemical structure of the gene (violation of the nucleotide sequence in DNA: * gene inserts of a pair or several nucleotides

Chromosomal mutations (chromosomal rearrangements, aberrations)
Causes - are caused by significant changes in the structure of chromosomes (redistribution of the hereditary material of chromosomes) In all cases, they arise as a result of ra

Polyploidy
Polyploidy - a multiple increase in the number of chromosomes in a cell (the haploid set of chromosomes -n is repeated not 2 times, but many times - up to 10 -1

The meaning of polyploidy
1. Polyploidy in plants is characterized by an increase in the size of cells, vegetative and generative organs - leaves, stems, flowers, fruits, root crops, etc. , y

Aneuploidy (heteroploidy)
Aneuploidy (heteroploidy) - a change in the number of individual chromosomes that is not a multiple of the haploid set (in this case, one or more chromosomes from a homologous pair are normal

Somatic mutations
Somatic mutations - mutations that occur in the somatic cells of the body Distinguish between gene, chromosomal and genomic somatic mutations

The law of homologous series in hereditary variability
· Discovered by N. I. Vavilov on the basis of the study of wild and cultivated flora of five continents 5. The mutation process in genetically related species and genera proceeds in parallel, in

Combination variability
Combinative variability - variability resulting from the regular recombination of alleles in the genotypes of offspring, due to sexual reproduction

Phenotypic variability (modification or non-hereditary)
Modification variability - evolutionarily fixed adaptive reactions of an organism to a change in the external environment without changing the genotype

The value of modification variability
1. most modifications have an adaptive value and contribute to the adaptation of the body to a change in the external environment 2. can cause negative changes - morphoses

Statistical patterns of modification variability
· Modifications of a single trait or property, measured quantitatively, form a continuous series (variation series); it cannot be built according to an unmeasurable feature or a feature that exists

Variation curve of the distribution of modifications in the variation series
V - trait variants P - frequency of occurrence of trait variants Mo - mode, or most

Differences in the manifestation of mutations and modifications
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Features of a person as an object of genetic research
1. It is impossible to purposefully select parental pairs and experimental marriages (impossibility of experimental crossing) 2. Slow generational change, which occurs on average after

Methods for studying human genetics
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twin method
The method consists in studying the patterns of inheritance of traits in single and dizygotic twins (the frequency of birth of twins is one case per 84 newborns)

Cytogenetic method
Consists of a visual study of mitotic metaphase chromosomes under a microscope Based on the method of differential staining of chromosomes (T. Kasperson,

Dermatoglyphics method
Based on the study of the relief of the skin on the fingers, palms and plantar surfaces of the feet (there are epidermal protrusions - ridges that form complex patterns), this trait is inherited

Population-statistical method
Based on the statistical (mathematical) processing of data on inheritance in large population groups (populations - groups that differ in nationality, religion, race, profession)

Somatic cell hybridization method
Based on the reproduction of somatic cells of organs and tissues outside the body in sterile nutrient media (cells are most often obtained from the skin, bone marrow, blood, embryos, tumors) and

Modeling method
· Theoretical basis biological modeling in genetics gives the law of homologous series hereditary variability N.I. Vavilova For modeling, certain

Genetics and medicine (medical genetics)
Studying the causes, diagnostic signs, possibilities of rehabilitation and prevention of human hereditary diseases (monitoring of genetic abnormalities)

Chromosomal diseases
The reason is a change in the number (genomic mutations) or structure of chromosomes (chromosomal mutations) of the karyotype of the germ cells of the parents (anomalies can occur at different

Polysomy on sex chromosomes
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Hereditary diseases of gene mutations
Cause - gene (point) mutations (changes in the nucleotide composition of a gene - insertions, substitutions, dropouts, transfers of one or more nucleotides; the exact number of genes in a person is unknown

Diseases controlled by genes located on the X or Y chromosome
Hemophilia - blood incoagulability Hypophosphatemia - loss of phosphorus and lack of calcium by the body, softening of the bones Muscular dystrophy - structural disorders

Genotypic level of prevention
1. Search and application of antimutagenic protective substances Antimutagens (protectors) are compounds that neutralize a mutagen before it reacts with a DNA molecule or remove it

Treatment of hereditary diseases
1. Symptomatic and pathogenetic - impact on the symptoms of the disease (the genetic defect is preserved and transmitted to offspring) n dieter

Gene Interaction
Heredity - a set of genetic mechanisms that ensure the preservation and transmission of the structural and functional organization of a species in a number of generations from ancestors

Interaction of allelic genes (one allelic pair)
There are five types of allelic interactions: 1. Complete dominance 2. Incomplete dominance 3. Overdominance 4. Codominance

complementarity
Complementarity - the phenomenon of the interaction of several non-allelic dominant genes, leading to the emergence of a new trait that is absent in both parents

Polymerism
Polymeria - interaction is not allelic genes, in which the development of one trait occurs only under the influence of several non-allelic dominant genes (polygene

Pleiotropy (multiple gene action)
Pleiotropy - the phenomenon of the influence of one gene on the development of several traits The reason for the pleiotropic influence of a gene is in the action of the primary product of this

Selection basics
Selection (lat. selektio - selection) - science and industry of agricultural. production, developing the theory and methods of creating new and improving existing plant varieties, animal breeds

Domestication as the first stage of selection
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Centers of origin and diversity of cultivated plants (according to N. I. Vavilov)
Center name Geographical position Homeland of cultivated plants

Artificial selection (selection of parent pairs)
Two types of artificial selection are known: mass and individual

Hybridization (crossing)
Allows you to combine certain hereditary traits in one organism, as well as get rid of undesirable properties In breeding, various crossing systems are used &n

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Outbreeding (outbreeding)
When crossing unrelated individuals, harmful recessive mutations that are in the homozygous state become heterozygous and do not have negative impact on the viability of the body

heterosis
Heterosis (hybrid strength) is a phenomenon of a sharp increase in the viability and productivity of first-generation hybrids during unrelated crossing (interbreeding).

Induced (artificial) mutagenesis
The frequency with the spectrum of mutations increases dramatically when exposed to mutagens (ionizing radiation, chemicals, extreme environmental conditions, etc.)

Interline hybridization in plants
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Vegetative propagation of somatic mutations in plants
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Methods of breeding and genetic work by I. V. Michurina
1. Systematically distant hybridization

Polyploidy
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Cell engineering
Cultivation of individual cells or tissues on artificial sterile nutrient media containing amino acids, hormones, mineral salts and other nutritional components (

Chromosomal engineering
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Animal breeding
Has a number of features in comparison with plant breeding, which objectively make it difficult to carry out 1. Only sexual reproduction is characteristic (lack of vegetative

domestication
It began about 10 - 5 thousand years ago in the Neolithic era (it weakened the effect of stabilizing natural selection, which led to an increase in hereditary variability and an increase in the selection efficiency

Crossing (hybridization)
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Outbreeding (outbreeding)
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Checking the breeding qualities of producers by offspring
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Stages of selection of microorganisms
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Tasks of biotechnology
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Products of microbiological synthesis
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Stages of the technological process of microbiological synthesis
Stage I - obtaining a pure culture of microorganisms containing only organisms of one species or strain Each species is stored in a separate test tube and goes to production and

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Stages of obtaining recombinant (hybrid) DNA molecules
1. Obtaining the original genetic material - the gene encoding the protein (trait) of interest The necessary gene can be obtained in two ways: artificial synthesis or extraction

Achievements in genetic engineering
The introduction of eukaryotic genes into bacteria is used for microbiological synthesis biologically active substances, which in nature are synthesized only by cells of higher organisms Synthesis

Problems and prospects of genetic engineering
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Chromosomal engineering in plants
It consists in the possibility of biotechnological replacement of individual chromosomes in plant gametes or the addition of new ones In the cells of each diploid organism there are pairs of homologous chromosomes

Cell and tissue culture method
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Clonial micropropagation of plants
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Cellular engineering in animals
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Hybridization of somatic cells in animals
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Environmental Biotechnology
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Bioenergy
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Bioconversion
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Engineering enzymology
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Biogeotechnology
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Properties of living matter
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Functions of living matter
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Land biomass
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soil biomass
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Biomass of the oceans
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Biological (biotic, biogenic, biogeochemical cycle) cycle of substances
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Biogeochemical cycles of individual chemical elements
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nitrogen cycle
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The carbon cycle
The main source of carbon carbon dioxide atmosphere and water The carbon cycle is carried out due to the processes of photosynthesis and cellular respiration The cycle begins with f

The water cycle
Carried out by solar energy Regulated by living organisms: 1. absorption and evaporation by plants 2. photolysis during photosynthesis (decomposition

Sulfur cycle
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Energy flow in the biosphere
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The emergence and evolution of the biosphere
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Noosphere
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Signs of the modern noosphere
1. Increasing amount of recoverable materials of the lithosphere - growth in the development of mineral deposits (now it exceeds 100 billion tons per year) 2. Mass consumption

Human influence on the biosphere
The current state of the noosphere is characterized by an ever-increasing prospect of an ecological crisis, many aspects of which are already manifesting themselves in full, creating a real threat to the existence

Energy production
q The construction of hydroelectric power plants and the creation of reservoirs causes flooding of large areas and the resettlement of people, raising the level of groundwater, erosion and waterlogging of the soil, landslides, loss of arable land

Food production. Depletion and pollution of the soil, reduction of the area of fertile soils
q Arable land covers 10% of the Earth's surface (1.2 billion ha) q Cause - overexploitation, imperfection of agricultural production: water and wind erosion and the formation of ravines, in

Reduction of natural biological diversity
q Human economic activity in nature is accompanied by a change in the number of animal and plant species, the extinction of entire taxa, and a decrease in the diversity of living things.

acid rain
q Increased acidity of rains, snow, fogs due to the emission of sulfur and nitrogen oxides from fuel combustion into the atmosphere q Acid precipitation reduces crops, destroys natural vegetation

Ways to solve environmental problems
In the future, a person will exploit the resources of the biosphere on an ever-increasing scale, since this exploitation is an indispensable and main condition for the very existence of h

Sustainable consumption and management of natural resources
q The most complete and comprehensive extraction of all minerals from the fields (due to the imperfection of the extraction technology, only 30-50% of the reserves are extracted from oil fields q Rec

Ecological strategy for the development of agriculture
q Strategic direction - increasing crop yields to feed a growing population without increasing acreage q Increasing crop yields without negative

Properties of living matter
1. Unity of the elementary chemical composition(98% are carbon, hydrogen, oxygen and nitrogen) 2. The unity of the biochemical composition - all living organisms

Hypotheses for the origin of life on Earth
There are two alternative concepts of the possibility of the origin of life on Earth: q abiogenesis - the emergence of living organisms from substances of inorganic nature

Stages of the development of the Earth (chemical prerequisites for the emergence of life)
1. Stellar stage of the Earth's history q Geological history Land started over 6 muzzles. years ago, when the Earth was a red-hot over 1000

The emergence of the process of self-reproduction of molecules (biogenic matrix synthesis of biopolymers)
1. Occurred as a result of the interaction of coacervates with nucleic acids 2. All the necessary components of the process of biogenic matrix synthesis: - enzymes - proteins - pr

Prerequisites for the emergence of the evolutionary theory of Ch. Darwin
Socio-economic background 1. In the first half of the XIX century. England became one of the most economically developed countries in the world with high level

· Set out in the book of Ch. Darwin "On the origin of species by natural selection or the preservation of favored breeds in the struggle for life", which was published

Variability
Substantiation of the variability of species To substantiate the position on the variability of living beings, Charles Darwin used common

Correlative (relative) variability
A change in the structure or function of one part of the body causes a coordinated change in the other or others, since the body is an integral system, the individual parts of which are closely interconnected

The main provisions of the evolutionary teachings of Ch. Darwin
1. All kinds of living creatures inhabiting the Earth have never been created by anyone, but arose naturally 2. Having arisen naturally, species slowly and gradually

The development of ideas about the form
Aristotle - used the concept of species when describing animals, which had no scientific content and was used as a logical concept D. Ray

Species criteria (signs of species identification)
Significance of species criteria in science and practice - determination of species belonging of individuals (species identification) I. Morphological - similarity of morphological inheritances

Population types
1. Panmictic - consist of individuals that reproduce sexually, cross-fertilized. 2. Clonial - from individuals that breed only without

mutation process
Spontaneous changes in the hereditary material of germ cells in the form of gene, chromosome and genomic mutations occur constantly throughout the entire period of life under the influence of mutations

Insulation
Isolation - stopping the flow of genes from population to population (restriction of the exchange genetic information between populations) Isolation value as fa

Primary insulation
Not directly related to the action of natural selection, is a consequence of external factors Leads to a sharp decrease or cessation of migration of individuals from other populations

Environmental isolation
Arises on the basis environmental differences the existence of different populations (different populations occupy different ecological niches) v For example, the trout of Lake Sevan p

Secondary isolation (biological, reproductive)
Is of decisive importance in the formation of reproductive isolation Arises as a result of intraspecific differences in organisms Arose as a result of evolution Has two iso

Migrations
Migrations - the movement of individuals (seeds, pollen, spores) and their characteristic alleles between populations, leading to a change in the frequencies of alleles and genotypes in their gene pools

population waves
Population waves ("waves of life") - periodic and non-periodic sharp fluctuations in the number of individuals in a population under the influence of natural causes (S. S.

Significance of population waves
1. Leads to an undirected and abrupt change in the frequencies of alleles and genotypes in the gene pool of populations (random survival of individuals during the wintering period can increase the concentration of this mutation by 1000 r

Gene drift (genetic-automatic processes)
Genetic drift (genetic-automatic processes) - random non-directional, not due to the action of natural selection, change in the frequencies of alleles and genotypes in m

The result of genetic drift (for small populations)
1. Causes the loss (p = 0) or fixation (p = 1) of alleles in the homozygous state in all members of the population, regardless of their adaptive value - homozygotization of individuals

Natural selection is the guiding factor of evolution
Natural selection- the process of preferential (selective, selective) survival and reproduction of the fittest individuals and non-survival or non-reproduction

Struggle for existence Forms of natural selection
Driving selection (Described by C. Darwin, modern teaching developed by D. Simpson, English) Driving selection - selection in

Stabilizing selection
· The theory of stabilizing selection was developed by the Russian acad. I. I. Shmagauzen (1946) Stabilizing selection - selection acting in stable

Other forms of natural selection
Individual selection - selective survival and reproduction of individuals that have an advantage in the struggle for existence and elimination of others

The main features of natural and artificial selection
Natural selection Artificial selection 1. Arose with the emergence of life on Earth (about 3 billion years ago) 1. Arose in the

Common features of natural and artificial selection
1. Initial (elementary) material - individual characteristics of the organism (hereditary changes - mutations) 2. Carried out according to the phenotype 3. Elementary structure - population

The struggle for existence is the most important factor in evolution
The struggle for existence is a complex relationship of an organism with abiotic (physical conditions of life) and biotic (relations with other living organisms) fact

Reproduction intensity
v One roundworm produces 200 thousand eggs per day; the gray rat gives 5 litters per year, 8 rats, which become sexually mature at the age of three months; offspring of one daphnia per summer

Interspecies struggle for existence
Occurs between individuals in populations different types Less acute than intraspecific, but its intensity increases if different species occupy similar ecological niches and have

Fight against adverse abiotic environmental factors
It is observed in all cases when individuals of the population find themselves in extreme physical conditions (excessive heat, drought, severe winter, excessive humidity, infertile soils, severe

The main discoveries in the field of biology after the creation of STE
1. Opening hierarchical structures DNA and protein, including the secondary structure of DNA - the double helix and its nucleoprotein nature 2. Deciphering the genetic code (its triplet

Signs of the organs of the endocrine system
1. They are relatively small in size (fractions or a few grams) 2. Anatomically unrelated 3. Synthesize hormones 4. Have an abundant network of blood vessels

Characteristics (signs) of hormones
1. Formed in the endocrine glands (neurohormones can be synthesized in neurosecretory cells) 2. High biological activity - the ability to quickly and strongly change the int

The chemical nature of hormones
1. Peptides and simple proteins (insulin, somatotropin, adenohypophysis tropic hormones, calcitonin, glucagon, vasopressin, oxytocin, hypothalamic hormones) 2. Complex proteins - thyrotropin, lute

Hormones of the middle (intermediate) share
Melanotropic hormone (melanotropin) - the exchange of pigments (melanin) in integumentary tissues Hormones of the posterior lobe (neurohypophysis) - oxytrcin, vasopressin

Thyroid hormones (thyroxine, triiodothyronine)
The composition of thyroid hormones certainly includes iodine and the amino acid tyrosine (0.3 mg of iodine is secreted daily in the hormones, therefore a person must receive daily with food and water

Hypothyroidism (hypothyroidism)
The cause of hypotherosis is a chronic deficiency of iodine in food and water. The lack of hormone secretion is compensated by the growth of the gland tissue and a significant increase in its volume.

Cortical hormones (mineralcorticoids, glucocorticoids, sex hormones)
The cortical layer is made up of epithelial tissue and consists of three zones: glomerular, fascicular and reticular, having different morphology and functions. Hormones related to steroids - corticosteroids

Adrenal medulla hormones (epinephrine, norepinephrine)
- The medulla consists of special yellow-staining chromaffin cells (these cells are located in the aorta, the branching point of the carotid artery and in the sympathetic nodes; they are all

Pancreatic hormones (insulin, glucagon, somatostatin)
Insulin (secreted by beta cells (insulocytes), is the simplest protein) Functions: 1. Regulation of carbohydrate metabolism (the only sugar lowering

Testosterone
Functions: 1. Development of secondary sexual characteristics (body proportions, muscles, growth of a beard, body hair, mental characteristics of a man, etc.) 2. Growth and development of reproductive organs

ovaries
1. Paired organs (sizes about 4 cm, weight 6-8 grams), located in the small pelvis, on both sides of the uterus 2. Consist of a large number(300 -400 thousand) t. follicles - structure

Estradiol
Functions: 1. Development of female genital organs: oviducts, uterus, vagina, mammary glands 2. Formation of female secondary sexual characteristics (body build, figure, fat deposition, in

Endocrine glands (endocrine system) and their hormones
Endocrine glands Hormones Functions Pituitary gland: - anterior lobe: adenohypophysis - middle lobe - posterior

Reflex. reflex arc
Reflex - the body's response to irritation (change) of the external and internal environment, carried out with the participation nervous system(the main form of activity

Feedback mechanism
The reflex arc does not end with the body's response to irritation (by the work of the effector). All tissues and organs have their own receptors and afferent nerve pathways suitable for sensory

Spinal cord
1. The most ancient part of the CNS of vertebrates (first appears in the cephalochordates - the lancelet) 2. In the process of embryogenesis, it develops from the neural tube 3. It is located in the bone

Skeletal motor reflexes
1. Patellar reflex (the center is localized in the lumbar segment); vestigial reflex from animal ancestors 2. Achilles reflex (in the lumbar segment) 3. Plantar reflex (with

Conductor function
The spinal cord has a two-way connection with the brain (stem and cerebral cortex); through the spinal cord, the brain is connected with the receptors and executive organs of the body

Brain
The brain and spinal cord develop in the embryo from the outer germ layer- ectoderm Located in the cavity of the brain skull Covered (like the spinal cord) by three shells

Medulla
2. In the process of embryogenesis, it develops from the fifth cerebral bladder of the neural tube of the embryo 3. It is a continuation spinal cord(the lower boundary between them is the exit point of the spine

reflex function
1. Protective reflexes: coughing, sneezing, blinking, vomiting, tearing 2. Food reflexes: sucking, swallowing, digestive juice secretion, motility and peristalsis

midbrain
1. In the process of embryogenesis from the third cerebral vesicle of the neural tube of the embryo 2. Covered with white matter, gray matter inside in the form of nuclei 3. Has the following structural components

Functions of the midbrain (reflex and conduction)
I. Reflex function (all reflexes are innate, unconditioned) 1. Regulation of muscle tone during movement, walking, standing 2. Orienting reflex

Thalamus (optical tubercles)
Represents paired accumulations of gray matter (40 pairs of nuclei), covered with a layer of white matter, inside - the III ventricle and reticular formation All nuclei of the thalamus are afferent, senses

Functions of the hypothalamus
1. The highest center of the nervous regulation of the cardiovascular system, the permeability of blood vessels 2. The center of thermoregulation 3. The regulation of the water-salt balance of the body

Functions of the cerebellum
The cerebellum is connected to all parts of the central nervous system; skin receptors, proprioceptors of the vestibular and motor apparatus, subcortex and cortex of the cerebral hemispheres The functions of the cerebellum are examined by

Telencephalon (large brain, large hemispheres of the forebrain)
1. In the process of embryogenesis, it develops from the first cerebral bladder of the neural tube of the embryo 2. It consists of two hemispheres (right and left), separated by a deep longitudinal fissure and connected

Cerebral cortex (cloak)
1. In mammals and humans, the surface of the cortex is folded, covered with convolutions and furrows, providing an increase in surface area (in humans it is about 2200 cm2

Functions of the cerebral cortex
Study methods: 1. Electrical stimulation of individual areas (the method of “implanting” electrodes into brain areas) 3. 2. Removal (extirpation) of individual areas

Sensory zones (areas) of the cerebral cortex
They are the central (cortical) sections of the analyzers, sensitive (afferent) impulses from the corresponding receptors are suitable for them Occupy a small part of the cortex

Functions of association zones
1. Communication between different areas of the cortex (sensory and motor) 2. Unification (integration) of all sensitive information entering the cortex with memory and emotions 3. Decisive

Features of the autonomic nervous system
1. It is divided into two sections: sympathetic and parasympathetic (each of them has a central and peripheral parts) 2. It does not have its own afferent (

Features of the departments of the autonomic nervous system
Sympathetic department Parasympathetic department 1. The central ganglia are located in the lateral horns of the thoracic and lumbar segments of the spinal

Functions of the autonomic nervous system
Most of the organs of the body are innervated by both the sympathetic and parasympathetic systems (dual innervation) Both departments have three kinds of actions on the organs - vasomotor,

Influence of the sympathetic and parasympathetic division of the autonomic nervous system
Sympathetic department Parasympathetic department 1. Accelerates the rhythm, increases the force of heart contractions 2. Expands the coronary vessels of the

Higher nervous activity of a person
Mental Mechanisms of Reflection: Mental Mechanisms of Designing the Future - Sensing

Features (signs) of unconditioned and conditioned reflexes
Unconditioned reflexes Conditioned reflexes

Methodology for the development (formation) of conditioned reflexes
Developed by I.P. Pavlov on dogs in the study of salivation under the action of light or sound stimuli, odors, touches, etc. (the salivary gland duct was brought out through the opening

Conditions for the development of conditioned reflexes
1. An indifferent stimulus must precede the unconditioned one (anticipatory action) 2. The average strength of an indifferent stimulus (with low and high strength, the reflex may not form

The meaning of conditioned reflexes
1. Underlying training, obtaining physical and mental skills 2. Subtle adaptation of vegetative, somatic and mental reactions to conditions with

Induction (external) braking
o Develops under the action of a foreign, unexpected, strong stimulus from the external or internal environment v Strong hunger, full bladder, pain or sexual arousal

Fading Conditional Inhibition
Develops with a systematic non-reinforcement of the conditioned stimulus with an unconditioned stimulus v If the conditioned stimulus is repeated at short intervals without reinforcing it without

Relationship between excitation and inhibition in the cerebral cortex
Irradiation - the spread of processes of excitation or inhibition from the focus of their occurrence to other areas of the cortex An example of the irradiation of the process of excitation

Causes of sleep
There are several hypotheses and theories of the causes of sleep: Chemical hypothesis - the cause of sleep is the poisoning of brain cells with toxic waste products, the image

REM (paradoxical) sleep
Comes after a period of slow sleep and lasts 10-15 minutes; then again replaced by slow sleep; repeated 4-5 times during the night Characterized by rapid

Features of higher nervous activity of a person
(differences from the GNI of animals) The channels for obtaining information about the factors of the external and internal environment are called signaling systems The first and second signaling systems are distinguished

Features of higher nervous activity of man and animals
Animal Human 1. Obtaining information about environmental factors only with the help of the first signaling system (analyzers) 2. Specific

Memory as a component of higher nervous activity
Memory is a set of mental processes that ensure the preservation, consolidation and reproduction of previous individual experience v Basic memory processes

Analyzers
All information about the external and internal environment of the body, necessary for interaction with it, a person receives with the help of the senses (sensory systems, analyzers) v The concept of analysis

Structure and functions of analyzers
Each analyzer consists of three anatomically and functionally related sections: peripheral, conductive and central Damage to one of the parts of the analyzer

The value of analyzers
1. Information to the body about the state and changes in the external and internal environment 2. The emergence of sensations and the formation on their basis of concepts and ideas about around the world, t. e.

Choroid (middle)
Located under the sclera, rich in blood vessels, consists of three parts: the anterior - the iris, the middle - the ciliary body and the posterior - the vascular itself

Features of the photoreceptor cells of the retina
Rods Cones 1. Quantity 130 million 2. Visual pigment - rhodopsin (visual purple) 3. Maximum amount on n

lens
· Located behind the pupil, has the shape of a biconvex lens with a diameter of about 9 mm, absolutely transparent and elastic. Covered with a transparent capsule, to which the zinnia ligaments of the ciliary body are attached

The functioning of the eye
Visual reception begins with photochemical reactions, starting in the rods and cones of the retina and consisting in the decay visual pigments under the action of light quanta. Exactly this

Vision hygiene
1. Injury prevention (goggles at work with traumatic objects - dust, chemical substances, shavings, splinters, etc.) 2. Eye protection from too bright light - the sun, el

outer ear
Representation of the auricle and external auditory canal The auricle - freely protruding on the surface of the head

Middle ear (tympanic cavity)
Lies inside the pyramid of the temporal bone Filled with air and communicates with the nasopharynx through a tube 3.5 cm long and 2 mm in diameter - the Eustachian tube Eustachian function

inner ear
It is located in the pyramid of the temporal bone It includes a bone labyrinth, which is a complex structure of channels Inside the bone

Perception of sound vibrations
The auricle picks up sounds and directs them to the external auditory canal. Sound waves cause vibrations of the tympanic membrane, which are transmitted from it through the system of levers of the auditory ossicles (

Hearing hygiene
1. Prevention of hearing injuries 2. Protection of the hearing organs from excessive strength or duration of sound stimuli - the so-called. "noise pollution", especially in noisy environments

biospheric
1. Represented by cellular organelles 2. Biological mesosystems 3. Mutations are possible 4. Histological research method 5. Beginning of metabolism 6. About

"Structure of a eukaryotic cell" 9. Cell organoid containing DNA 10. Has pores 11. Performs a compartmental function in the cell 12. Function

Cell Center
Verification thematic digital dictation on the topic "Cell Metabolism" 1. Carried out in the cytoplasm of the cell 2. Requires specific enzymes

Thematic digital programmed dictation
on the topic "Energy exchange" 1. Hydrolysis reactions are carried out 2. End products - CO2 and H2 O 3. End product - PVC 4. NAD is restored

oxygen stage
Thematic digital programmed dictation on the topic "Photosynthesis" 1. Photolysis of water is carried out 2. Recovery occurs

Cell Metabolism: Energy Metabolism. Photosynthesis. Protein biosynthesis” 1. Carried out in autotrophs 52. Transcription is carried out 2. Associated with the functioning

The main features of the kingdoms of eukaryotes
Kingdom of Plants Kingdom of Animals 1. They have three sub-kingdoms: - lower plants (true algae) - red algae

Features of types of artificial selection in breeding
Mass selection Individual selection 1. Many individuals with the most pronounced hosts are allowed to breed.

Common features of mass and individual selection
1. Carried out by man with artificial selection 2. Only individuals with the most pronounced desired trait are allowed for further reproduction 3. Can be repeated

Lipids in the composition of membranes are assigned, first of all, structural properties - they create a bilayer, or matrix, in which the active components of the membrane - proteins - are located. It is proteins that give various membranes their uniqueness and provide specific properties. Numerous membrane proteins perform the following main functions: they determine the transfer of substances through membranes (transport functions), carry out catalysis, provide processes of photo- and oxidative phosphorylation, DNA replication, translation and modification of proteins, signal reception and transmission of a nerve impulse, etc.

Channels, in turn, can be divided into two main groups: voltage-dependent and chemically regulated. An example of a voltage-dependent channel is the Na + channel, its operation is regulated by a change in the electric field voltage. In other words, these channels open and close in response to a change transmembrane potential. Chemically regulated channels

Enzymatic functions of membrane proteins. A wide variety of enzymes function in cell membranes. Some of them are localized in the membrane, finding there a suitable environment for the conversion of hydrophobic compounds, others, due to the participation of membranes, are located in them in strict order, catalyzing successive stages of vital processes, and others need the assistance of lipids to stabilize their conformation and maintain activity. Enzymes were found in biomembranes - representatives of all known classes. They can penetrate the membrane through, be present in it in a dissolved form, or, being peripheral proteins, bind to membrane surfaces in response to some signal. The following characteristic types of membrane enzymes can be distinguished:

2) transmembrane enzymes involved in the transport of substances. Transport proteins that couple the transfer of a substance with ATP hydrolysis, for example, have a catalytic function;

3) enzymes that catalyze the conversion of membrane-bound substrates. These enzymes are involved in the metabolism of membrane components: phospholipids, glycolipids, steroids, etc.

The cytoskeleton is formed from three types of fibers:

1) microfilaments(diameter ~ 6 nm). They are filamentous organelles - polymers of the globular protein actin and other proteins associated with it;

2) intermediate filaments (diameter 8-10 nm). Formed by keratins and related proteins;

3) microtubules(diameter ~ 23 nm) - long tubular structures.

To membrane proteins include proteins that are embedded in or associated with the cell membrane or the membrane of a cell organelle. About 25% of all proteins are membrane proteins.

Biochemical classification

According to the biochemical classification, membrane proteins are divided into integral and peripheral.

Integral membrane proteins are firmly embedded in the membrane and can only be removed from the lipid environment with the help of detergents or non-polar solvents. In relation to the lipid bilayer, integral proteins can be transmembrane polytopic or integral monotopic.
Peripheral membrane proteins are monotopic proteins. They are either bound by weak bonds to the lipid membrane or are associated with integral proteins by hydrophobic, electrostatic, or other non-covalent forces. Thus, unlike integral proteins, they dissociate from the membrane when treated with the appropriate aqueous solution(for example, low or high pH, high salt concentration, or under the influence of a chaotropic agent). This dissociation does not require the destruction of the membrane.

Membrane proteins can be built into the membrane due to fatty acid or prenyl residues or glycosylphosphatidylinositol attached to the protein during their post-translational modification.

Another important point is the methods of attaching proteins to the membrane:

1. Binding to proteins immersed in the bilayer. Examples include the F1 part of H + -ATRase, which binds to the Fo part embedded in the membrane; some cytoskeletal proteins can also be mentioned.

2. Binding to the bilayer surface. This interaction is primarily electrostatic in nature (eg myelin basic protein) or hydrophobic (eg surfactant peptides and possibly phospholipases). On the surface of some membrane proteins there are hydrophobic domains that are formed due to the features of the secondary or tertiary structure. These surface interactions can be used in addition to other interactions such as transmembrane anchoring.

3. Binding with a hydrophobic "anchor"; this structure usually appears as a sequence of non-polar amino acid residues (for example, in cytochrome 65). Some membrane proteins use covalently linked fatty acids or phospholipids as anchors.

4. Transmembrane proteins. Some of them cross the membrane only once (for example, glycophorin), others - several times (for example, lactose permease; bacteriorhodopsin).

Membrane lipids

Membrane lipids are amphipathic molecules that spontaneously form bilayers. Lipids are insoluble in water, but readily soluble in organic solvents. In most animal cells, they make up about 50% of the mass of the plasma membrane. There are approximately 5 x 100 thousand lipid molecules in a 1 x 1 μm section of the lipid bilayer. Therefore, the plasma membrane of a small animal cell contains approximately 10 lipid molecules. There are three main types of lipids in the cell membrane:

1) phospholipids (the most common type); complex lipids containing glycerol, fatty acids, phosphoric acid and a nitrogenous compound.

A typical phospholipid molecule has a polar head and two hydrophobic hydrocarbon tails. The length of the tails varies from 14 to 24 carbon atoms in the chain. One of the tails typically contains one or more cis double bonds (unsaturated hydrocarbon) while the other (saturated hydrocarbon) has no double bonds. Each double bond causes a kink in the tail. These differences in tail length and saturation of hydrocarbon chains are important because they affect membrane fluidity.

Amphipathic molecules in an aqueous environment usually aggregate, with hydrophobic tails hidden and hydrophilic heads remaining in contact with water molecules. Aggregation of this type is carried out in two ways: either by the formation of spherical micelles with tails turned inward, or by the formation of bimolecular films, or bilayers, in which hydrophobic tails are located between two layers of hydrophilic heads.

The two main phospholipids that are present in plasma are phosphatidylcholine (lecithin) and sphingomyelin. Synthesis of phospholipids occurs in almost all tissues, but the main source of plasma phospholipids is the liver. The small intestine also supplies plasma with phospholipids, namely lecithin, as part of the chylomicrons. Most of the phospholipids that enter the small intestine (including in the form of complexes with bile acids) are subjected to preliminary hydrolysis by pancreatic lipase. This explains why polyunsaturated lecithin added to food does not affect plasma phospholipid content of linoleate more than equivalent amounts of corn oil triglycerides.

Phospholipids are an integral component of all cell membranes. Phosphatidylcholine and sphingomyelin are constantly exchanged between plasma and erythrocytes. Both of these phospholipids are present in plasma as constituents of lipoproteins, where they play key role by maintaining non-polar lipids such as triglycerides and cholesterol esters in a soluble state. This property reflects the amphipathic nature of phospholipid molecules - nonpolar fatty acid chains are able to interact with the lipid environment, and polar heads - with the aqueous environment (Jackson R.L. ea, 1974).

2) Cholesterol. Cholesterol is a sterol containing a four-ring steroid nucleus and a hydroxyl group.

This compound is found in the body both as a free sterol and as ester with one of the long chain fatty acids. Free cholesterol is a component of all cell membranes and is the main form in which cholesterol is present in most tissues. The exceptions are the adrenal cortex, plasma and atheromatous plaques, where cholesterol esters predominate. In addition, a significant part of the cholesterol in the intestinal lymph and in the liver is also esterified.

Cholesterol is found in lipoproteins either in free form or as esters with long-chain fatty acids. It is synthesized in many tissues from acetyl-CoA and excreted in bile as free cholesterol or bile salts. Cholesterol is a precursor to other steroids, namely corticosteroids, sex hormones, bile acids, and vitamin D. It is a compound typical of animal metabolism and is found in significant amounts in animal products such as egg yolk, meat, liver and brain.

Eukaryotic plasma membranes contain a fairly large amount of cholesterol - approximately one molecule for each phospholipid molecule. In addition to regulating flow, cholesterol increases the mechanical strength of the bilayer. Cholesterol molecules are oriented in the bilayer in such a way that they hydroxyl groups attached to the polar heads of phospholipid molecules

3) glycolipids

Glycolipids are lipid molecules belonging to the class of oligosaccharide-containing lipids that are found only in the outer half of the bilayer, and their sugar groups are oriented towards the cell surface.

Glycolipids are sphingolipids in which a fatty acid residue is attached to the NH group of sphingazine, and the following groups are attached to the oxygen of sphingazine: oligosaccharide chains, Gal, Glc, GalNAc (neuraminic acid) - gangliosides. Gal or Glc are cerebrosides. sulfosaccharides Glc-SO3H, Gal-SO3H are sulfolipids.

Glycolipids are found on the surface of all plasma membranes, but their function is unknown. Glycolipids make up 5% of the lipid molecules of the outer monolayer and vary greatly between species and even within different tissues of the same species. In animal cells, they are synthesized from sphingosine, a long amino alcohol, and are called glycosphingolipids.

Their structure is generally similar to the structure of phospholipids formed from glycerol. All glycolipid molecules differ in the number of sugar residues in their polar heads. One of the simplest glycolipids is galactocerebroside.