Human anatomy. Cell structure
Cells are divided into prokaryotic and eukaryotic. The first are algae and bacteria, which contain genetic information in one single organelle, the chromosome, while eukaryotic cells, which make up more complex organisms, such as the human body, have a clearly differentiated nucleus, which contains several chromosomes with genetic material.
eukaryotic cell
prokaryotic cell
Structure
Cellular or cytoplasmic membrane
The cytoplasmic membrane (shell) is a thin structure that separates the contents of the cell from the environment. It consists of a double layer of lipids with protein molecules approximately 75 angstroms thick.
The cell membrane is continuous, but it has numerous folds, convolutions, and pores, which allows you to regulate the passage of substances through it.
Cells, tissues, organs, systems and apparatuses
Cells, The human body is a component of elements that work together in order to effectively perform all vital functions.
Textile- These are cells of the same shape and structure, specialized in performing the same function. Various tissues combine to form organs, each of which performs a specific function in a living organism. In addition, organs are also grouped into a system to perform a specific function.
Fabrics:
epithelial- Protects and coats the surface of the body and internal surfaces of organs.
Connective- fat, cartilage and bone. Performs various functions.
muscular- smooth muscle tissue, striated muscle tissue. Contracts and relaxes muscles.
nervous- neurons. Generates and transmits and receives impulses.
Cell size
The size of the cells is very different, although in general it ranges from 5 to 6 microns (1 micron = 0.001 mm). This explains the fact that many cells could not be seen before the invention of the electron microscope, whose resolution is from 2 to 2000 angstroms (1 angstrom \u003d 0.000 000 1 mm). The size of some microorganisms is less than 5 microns, but there are also giant cells. Of the most famous - this is the yolk of bird eggs, an egg about 20 mm in size.
There are even more striking examples: the cell of acetabularia, a single-celled marine alga, reaches 100 mm, and ramie, a herbaceous plant, - 220 mm - more than a palm.
From parents to children thanks to chromosomes
The cell nucleus undergoes various changes when the cell begins to divide: the membrane and nucleoli disappear; at this time, chromatin becomes denser, eventually forming thick threads - chromosomes. The chromosome consists of two halves - chromatids connected at the site of constriction (centrometer).
Our cells, like all cells of animals and plants, are subject to the so-called law of numerical constancy, according to which the number of chromosomes of a certain species is constant.
In addition, chromosomes are distributed in pairs that are identical to each other.
Each cell in our body has 23 pairs of chromosomes, which are several elongated DNA molecules. The DNA molecule takes the form of a double helix, consisting of two groups of sugar phosphate, from where nitrogenous bases (purines and pyramidins) protrude in the form of steps of a spiral staircase.
Along each chromosome are genes responsible for heredity, the transfer of gene traits from parents to children. They determine the color of the eyes, skin, shape of the nose, etc.
Mitochondria
Mitochondria are round or elongated organelles distributed throughout the cytoplasm, containing an aqueous solution of enzymes, capable of carrying out numerous chemical reactions, such as cellular respiration.
This process releases the energy that the cell needs to perform its vital functions. Mitochondria are found mainly in the most active cells of living organisms: cells of the pancreas and liver.
cell nucleus
The nucleus, one in every human cell, is its main component, since it is the organism that controls the functions of the cell and the carrier of hereditary traits, which proves its importance in reproduction and the transmission of biological heredity.
In the core, the size of which ranges from 5 to 30 microns, the following elements can be distinguished:
- Nuclear shell. It is double and allows substances to pass between the nucleus and the cytoplasm due to its porous structure.
- nuclear plasma. Light, viscous liquid in which the rest of the nuclear structures are immersed.
- Nucleus. Spherical body, isolated or in groups, involved in the formation of ribosomes.
- Chromatin. A substance that can take on various colors, consisting of long strands of DNA (deoxyribonucleic acid). Threads are particles, genes, each of which contains information about a specific function of the cell.
The nucleus of a typical cell
Skin cells live an average of one week. Erythrocytes live 4 months, and bone cells - from 10 to 30 years.
Centrosome
The centrosome is usually located near the nucleus and plays a critical role in mitosis, or cell division.
It consists of 3 elements:
- Diplosome. It consists of two centrioles - cylindrical structures located perpendicularly.
- Centrosphere. The translucent substance in which the diplosome is immersed.
- Aster. A radiant formation of filaments emerging from the centrosphere, essential for mitosis.
Golgi complex, lysosomes
The Golgi complex consists of 5-10 flat disks (plates), in which the main element is distinguished - a cistern and several dictyosomes, or an accumulation of cistern. These dictyosomes separate and distribute evenly during mitosis, or cell division.
Lysosomes, the “stomach” of the cell, are formed from the vesicles of the Golgi complex: they contain digestive enzymes that allow them to digest food entering the cytoplasm. Their interior, or mycus, is lined with a thick layer of polysaccharides that prevent these enzymes from breaking down their own cellular material.
Ribosomes
Ribosomes are cellular organelles with a diameter of about 150 angstroms that are attached to the membranes of the endoplasmic reticulum or are freely located in the cytoplasm.
They consist of two subunits:
- the large subunit consists of 45 protein molecules and 3 RNA (ribonucleic acid);
- the smaller subunit consists of 33 protein molecules and 1 RNA.
Ribosomes combine into polysomes with the help of an RNA molecule and synthesize proteins from amino acid molecules.
Cytoplasm
Cytoplasm is an organic mass located between the cytoplasmic membrane and the nuclear envelope. It contains an internal environment - hyaloplasm - a viscous liquid consisting of a large amount of water and containing proteins, monosaccharides and fats in dissolved form.
It is a part of the cell endowed with vital activity, because various cell organelles move inside it and biochemical reactions occur. Organelles perform the same role in the cell as the organs in the human body: they produce vital substances, generate energy, perform the functions of digestion and excretion of organic substances, etc.
Approximately one third of the cytoplasm is water.
In addition, the cytoplasm contains 30% organic substances (carbohydrates, fats, proteins) and 2-3% inorganic substances.
Endoplasmic reticulum
The endoplasmic reticulum is a network-like structure formed by the wrapping of the cytoplasmic membrane into itself.
This process, known as invagination, is thought to have led to more complex creatures with greater protein requirements.
Depending on the presence or absence of ribosomes in the shells, two types of networks are distinguished:
1. The endoplasmic reticulum is folded. A collection of flat structures interconnected and communicating with the nuclear membrane. A large number of ribosomes are attached to it, so its function is to accumulate and release proteins synthesized in ribosomes.
2. Endoplasmic reticulum is smooth. A network of flat and tubular elements that communicates with the folded endoplasmic reticulum. Synthesizes, secretes and transports fats throughout the cell, together with the proteins of the folded reticulum.
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