The structure and functions of proteins
Lesson learning new material in the 10th grade. Students already studied this material in grade 9, so some concepts are already known to them. Accordingly, a dialogue is being held with the guys about the structure and functions of proteins. With the help of a teacher, students will learn about the classification of enzymes.
In order to intensify the activity of students in the lesson, interesting facts about proteins are given that help the children and aim them at further assimilation of new material. Also for these purposes it is proposed to conduct laboratory work. In this lesson, the bulk of the material being studied is recorded in the form of tables, diagrams, which the teacher builds during the lesson together with the students. The quality of the studied material is checked in the form of a frontal survey. The lesson is designed for both auditory and visual children.
The purpose of the lesson: to give an idea of the structure and function of proteins.
Objectives: to continue expanding and deepening knowledge of the most important organic substances of the cell based on the study of the structure and function of proteins, to form knowledge of the functions of proteins and their most important role in the organic world, to continue the formation of the ability to identify relationships between the structure and functions of substances.
Basic concepts: proteins, proteins, proteids, peptide, peptide bond, simple and complex proteins, primary, secondary, tertiary and quaternary structures of proteins, denaturation.
Teaching tools: general biology tables illustrating the structure of protein molecules; laboratory equipment for the laboratory work “The splitting of hydrogen peroxide with the help of enzymes contained in elodea leaf whips”.
During the classes
I. Learning new material.
1. A teacher's story (or a fragment of a lecture) about the structural features of protein molecules as biopolymers, consisting of a large number of different amino acids, between which polymerization occurs based on a peptide bond. Sketching and writing on the board and in students' notebooks.
2. Independent study by students of the text of the textbook (P.42) on the classification of proteins.
3. A conversation about the levels of organization of a protein molecule and the chemical basis of each of the four levels (structures) of this molecule, about denaturation as the loss of a protein molecule of its natural structure.
The structure of the protein molecule.
| protein structure | Characteristic | Communication type | Scheme (students draw on their own) |
| Primary | Linear structure - the sequence of amino acids in the polypeptide chain, which determines all other structures of the molecule, as well as the properties and functions of the protein. | Peptide. | |
| Secondary | Twisting the polypeptide chain into a spiral or folding into an "accordion". | Hydrogen bonds. | |
| Tertiary | Globular protein: packaging of the secondary structure into a globule; fibrillar protein: several secondary structures stacked in parallel layers, or twisting of several secondary structures like a rope into a supercoil. |
Ionic, hydrogen, disulfide, hydrophobic. | |
| Quaternary | Occurs rarely. A complex of several organic tertiary structures and an inorganic substance such as hemoglobin. | Ionic, hydrogen, hydrophobic. |
4. The teacher's story about the diversity of protein functions with a brief note in notebooks of the essence of functions: structural, enzymatic, transport, protective, regulatory, energy, signal.
5. Laboratory work “The breakdown of hydrogen peroxide with the help of enzymes contained in leaf cells elodei".
Working process:
a. Prepare a micropreparation of an elodea leaf and examine it under a microscope.
b. Drop a little hydrogen peroxide on the micropreparation and once again consider the state of the Elodea leaf cells.
in. Explain what causes the release of bubbles from leaf aunts, what kind of gas is it, what substances can hydrogen peroxide split into, what enzymes are involved in this process?
d. Drop a drop of peroxide on a glass slide and, having examined it under a microscope, describe the observed picture. Compare the state of hydrogen peroxide in the elodea leaf and on the glass, draw conclusions.
Upon completion of the laboratory work, a conversation should be held about the biochemical reactions that occur with the participation of protein catalysts-enzymes as the basis of the vital activity of cells and organisms.
The chemical properties of proteins are due to their different amino acid composition. There are proteins that are highly soluble in water and completely insoluble, chemically active and resistant to the action of various agents, capable of shortening and stretching, etc.
Under the influence of various factors - high temperature, the action of chemicals, radiation, mechanical stress - the destruction of the structures of the protein molecule can occur. Violation of the natural structure of the protein is called denaturation. If the impact of these factors was short-lived and not strong, then the protein can return its natural structure - reversible denaturation (renaturation), but if the impact was long or strong, then not only the tertiary and secondary structures are disturbed, but also the primary one - irreversible denaturation (Fig. 3).
Protein functions.
| Function | Characteristic |
| 1. Construction (structural). | They are part of cell membranes and cell organelles (lipoproteins and glycoproteins), participate in the formation of the walls of blood vessels, cartilage, tendons (collagen) and hair (keratin). |
| 2. Motor | It is provided by contractile proteins (actin and myosin), which cause the movement of cilia and flagella, muscle contraction, movement of chromosomes during cell division, and movement of plant organs. |
| 3. Transport. | Many chemical compounds bind and carry with the blood stream, for example, hemoglobin and myoglobin transport oxygen, blood serum proteins carry hormones, lipids and fatty acids, various biologically active substances. |
| 4. Protective. | The production of antibodies (immunoglobulins) in response to the penetration of foreign substances (antigens) into it, which provide immunological protection; participation in the processes of blood coagulation (fibrinogen and prothrombin). |
| 5, Signal (receptor). | Reception of signals from the external environment and transmission of commands to the cell due to changes in the tertiary structure of proteins built into the membrane in response to the action of environmental factors. For example, glycoproteins (embedded in glycocal X), opsin (an integral part of the light-sensitive pigments rhodopsin and iodopsin), phytochrome (light-sensitive plant protein). |
| 6. Regulatory. | Protein hormones affect metabolism, i.e. provide homeostasis, regulate growth, reproduction, development and other vital processes. For example, insulin regulates blood glucose levels, thyroxine regulates physical and mental development, and so on. |
| 7. Catalytic (enzymatic). | Enzyme proteins accelerate the biochemical processes in the cell. |
| K. Reserve | Reserve proteins of animals: albumin (eggs) stores water, ferritin - iron in the cells of the liver, spleen; myoglobin - oxygen in muscle fibers, casein (milk) and seed proteins - a source of nutrition for the embryo. |
| 9. Food (the main source of amino acids). | Food proteins are the main source of amino acids (especially essential ones) for animals and humans; casein (milk protein) is the main source of amino acids for young mammals. |
| 10. Energy. | They are a source of energy - when 1 g of protein is oxidized, 17.6 kJ of energy is released, but the body uses proteins as an energy source very rarely, for example, during prolonged starvation. |
Enzymes (enzymes) are specific proteins that are present in all living organisms and play the role of biological catalysts.
Chemical reactions in a living cell proceed at a moderate temperature, normal pressure and a neutral environment. Under such conditions, the reactions of synthesis or decomposition of substances would proceed very slowly if they were not exposed to enzymes. Enzymes speed up a reaction without changing its overall result by lowering the activation energy. This means that in their presence, much less energy is required to impart reactivity to the molecules that react. Enzymes differ from chemical catalysts in a high degree of specificity, i.e., an enzyme catalyzes only one reaction or acts on only one type of bond. The rate of enzymatic reactions depends on many factors - the nature and concentration of the enzyme and substrate, temperature, pressure, acidity of the medium, the presence of inhibitors, etc.
Classification of enzymes.
| Group | Catalyzed reactions, examples |
| Oxidoreductases. | Redox reactions: the transfer of hydrogen (H) and oxygen (O) atoms or electrons from one substance to another, while the first is oxidized and the second is reduced. Participate in all processes of biological oxidation, for example, inhalation: AN + B A BH (oxidized) or A + O AO (reduced). |
| Transferases. | The transfer of a group of atoms (methyl, acyl, phosphate or amino group) from one substance to another. For example, the transfer of phosphoric acid residues from ATP to glucose or fructose under the action of phototransferases: ATP + glucose glucose-6-phosphate + ADP. |
| Hydrolases. | Reactions of the splitting of complex organic compounds into simpler ones by adding water molecules at the site of breaking the chemical bond (hydrolysis). For example, amylase (hydrolyzes starch), lipase (breaks down fats), trypsin (breaks down proteins), etc.: AB + H 2 0 AON + VN. |
| Liase | Non-hydrolytic addition to or removal of a group of atoms from a substrate. In this case, C-C, C-N, C-O, C-S bonds can be broken. For example, decarboxylase cleaves off a carboxyl group: |
| Isomerases | Intramolecular rearrangements, the transformation of one isomer into another (isomerization): glucose-6-phosphate glucose-1-phosphate. |
| Ligases (synthetases) | Reactions of the connection of two molecules with the formation of new bonds C–O, C–S, C–N, C–C, using the energy of ATP. For example, the enzyme valine-tRNA synthetase, under the action of which the valine-tRNA complex is formed: ATP + valine + tRNA ADP + H 3 P0 4 + valine-tRNA. |
The mechanism of enzyme action is shown in fig. 4. In the molecule of each enzyme there is an active center - this is one or more sites in which catalysis occurs due to close contact between the molecules of the enzyme and a specific substance (substrate). The active center is either a functional group (for example, an OH group) or a single amino acid. The active center can be formed by metal ions bound to the enzyme, vitamins and other non-protein compounds - coenzymes or cofactors. The shape and chemical structure of the active center are such that only certain substrates can bind to it due to their ideal correspondence (complementarity) to each other.
The enzyme molecule changes the globular shape of the substrate molecule. The substrate molecule, when attached to the enzyme, also changes its configuration within certain limits to increase the reactivity of the functional groups of the center.
At the final stage of the chemical reaction, the enzyme-substrate complex decomposes with the formation of final products and a free enzyme. The active center released in this case can accept new substrate molecules.
II. A generalizing conversation about the fundamental role of proteins as the most necessary chemical compounds for the life and activity of all life on Earth.
III. Consolidation of knowledge in the process of conversation with the help of the following questions:
- What organic substances of the cell can be called the most important?
- How is an endless variety of proteins created?
- What are the monomers of a protein biopolymer?
- How is a peptide bond formed?
- What is the primary structure of a protein?
- How does the transition of the primary structure of protein molecules to the secondary, and then to the tertiary and quaternary?
- What functions can protein molecules perform?
- What is the reason for the diversity of functions of protein molecules?
- Give examples of proteins that perform a variety of functions. You can use the following pattern to answer:
Biological functions of proteins.
It is interesting.
Many molecules are very large both in length and in molecular weight. Thus, the molecular weight of insulin is 5700, the ribonuclease enzyme protein is 127 OOO, egg albumin is 36 OOO, and hemoglobin is 65 OOO. Different proteins contain a variety of amino acids. A set of all twenty types of amino acids contains: milk casein, muscle myosin and egg albumin. In the protein-enzyme ribonuclease - 19, in insulin - 18 amino acids. A team of scientists led by Academician Yu.A. Ovchinnikov managed to decipher the complex structure of the rhodopsin protein responsible for the process of visual perception.
The blood of octopuses, molluscs, and spiders is blue because their oxygen carrier is not red hemoglobin containing iron atoms, but hemocyanin with copper atoms.
Almost half of the proteins we need, carbohydrates, 70-80% of vitamins, a significant amount of mineral salts, amino acids and other nutrients are found in bread.
American scientists have isolated from a plant (Pentadipland family), growing in West Africa, a protein that is 2,000 times sweeter than sugar. This sixth sweet protein known to science, called brazein, is found in fruits that are eagerly eaten by local monkeys. Biochemists have deciphered the structure of sweet protein molecules, each of them contains 54 amino acid residues.
IV. Homework: Study § 11, answer questions on p. 46. Prepare reports or abstracts on the topics: “Proteins are biopolymers of life”, “Protein functions are the basis of the life of every organism on Earth”, “Denaturation and renaturation, its practical significance”, “Variety of enzymes, their role in the life of cells and organisms” and etc.
Resources used:
- Kamensky A.A. General biology 10–11: textbook for general education. institutions. - M.: Drofa, 2006.
- Kozlova T.A. Thematic and lesson planning in biology for the textbook by A.A. Kamensky and others “General Biology 10–11”. - M .: Publishing house "Exam", 2006.
- Biology. General biology. 10-11 grades: workbook for the textbook Kamensky A.A. et al. “General biology 10–11” – M.: Drofa, 2011.
- Kirilenko A.A. Molecular biology. Collection of tasks for preparing for the exam: levels A, B, C: teaching aid. - Rostov n / a: Legion, 2011.
