Why are molecules of proteins, nucleic acids, carbohydrates and lipids considered as biopolymers only in the cell? What came first: nucleic acid or protein What fat-like substances do you know?
Current page: 2 (book has 16 pages total) [available reading passage: 11 pages]
Biology– life science is one of the oldest sciences. Man has accumulated knowledge about living organisms over thousands of years. As knowledge accumulated, biology differentiated into independent sciences (botany, zoology, microbiology, genetics, etc.). The importance of border disciplines connecting biology with other sciences - physics, chemistry, mathematics, etc., is increasingly increasing. As a result of integration, biophysics, biochemistry, space biology, etc. arose.
Currently, biology is a complex science, formed as a result of the differentiation and integration of different disciplines.
In biology, various research methods are used: observation, experiment, comparison, etc.
Biology studies living organisms. They are open biological systems that receive energy and nutrients from the environment. Living organisms respond to external influences, contain all the information they need for development and reproduction, and are adapted to a specific habitat.
All living systems, regardless of the level of organization, have common features, and the systems themselves are in continuous interaction. Scientists distinguish the following levels of organization of living nature: molecular, cellular, organismal, population-species, ecosystem and biosphere.
Chapter 1. Molecular level
The molecular level can be called the initial, deepest level of organization of living things. Every living organism consists of molecules of organic substances - proteins, nucleic acids, carbohydrates, fats (lipids), called biological molecules. Biologists study the role of these essential biological compounds in the growth and development of organisms, the storage and transmission of hereditary information, metabolism and energy conversion in living cells and other processes.
In this chapter you will learn
What are biopolymers;
What structure do biomolecules have?
What functions do biomolecules perform?
What are viruses and what are their features?
§ 4. Molecular level: general characteristics
1. What is a chemical element?
2. What are called an atom and a molecule?
3. What organic substances do you know?
Any living system, no matter how complexly organized it may be, manifests itself at the level of functioning of biological macromolecules.
By studying living organisms, you learned that they consist of the same chemical elements, as inanimate. Currently, more than 100 elements are known, most of them are found in living organisms. The most common elements in living nature include carbon, oxygen, hydrogen and nitrogen. It is these elements that form molecules (compounds) of the so-called organic matter.
The basis of all organic compounds carbon serves. It can come into contact with many atoms and their groups, forming chains that differ in chemical composition, structure, length and shape. Molecules are formed from groups of atoms, and from the latter - more complex molecules that differ in structure and function. These organic compounds that make up the cells of living organisms are called biological polymers or biopolymers.
Polymer(from Greek policies- numerous) - a chain consisting of numerous links - monomers, each of which is relatively simple. A polymer molecule can consist of many thousands of interconnected monomers, which can be the same or different (Fig. 4).
Rice. 4. Scheme of the structure of monomers and polymers
The properties of biopolymers depend on the structure of their molecules: on the number and variety of monomer units that form the polymer. All of them are universal, since they are built according to the same plan for all living organisms, regardless of species.
Each type of biopolymer is characterized by a specific structure and function. Yes, molecules proteins are the main structural elements cells and regulate the processes occurring in them. Nucleic acids participate in the transfer of genetic (hereditary) information from cell to cell, from organism to organism. Carbohydrates And fats They are the most important sources of energy necessary for the life of organisms.
Exactly on molecular level All types of energy are converted and metabolism occurs in the cell. The mechanisms of these processes are also universal for all living organisms.
At the same time, it turned out that the diverse properties of biopolymers that make up all organisms are due to different combinations of just a few types of monomers, forming many variants of long polymer chains. This principle underlies the diversity of life on our planet.
The specific properties of biopolymers appear only in a living cell. Once isolated from cells, biopolymer molecules lose their biological essence and are characterized only by the physicochemical properties of the class of compounds to which they belong.
Only by studying the molecular level can one understand how the processes of the origin and evolution of life on our planet proceeded, what are the molecular basis of heredity and metabolic processes in a living organism.
Continuity between the molecular level and the next cellular level is ensured by the fact that biological molecules are the material from which supramolecular - cellular - structures are formed.
Organic substances: proteins, nucleic acids, carbohydrates, fats (lipids). Biopolymers. Monomers
Questions
1. What processes do scientists study at the molecular level?
2. What elements predominate in the composition of living organisms?
3. Why are molecules of proteins, nucleic acids, carbohydrates and lipids considered as biopolymers only in the cell?
4. What is meant by the universality of biopolymer molecules?
5. How is the diversity of properties of biopolymers that make up living organisms achieved?
Tasks
What biological patterns can be formulated based on the analysis of the text of the paragraph? Discuss them with class members.
§ 5. Carbohydrates
1. What substances related to carbohydrates do you know?
2. What role do carbohydrates play in a living organism?
3. As a result of what process are carbohydrates formed in the cells of green plants?
Carbohydrates, or saccharides, is one of the main groups of organic compounds. They are part of the cells of all living organisms.
Carbohydrates are made up of carbon, hydrogen and oxygen. They received the name “carbohydrates” because most of them have the same ratio of hydrogen and oxygen in the molecule as in the water molecule. The general formula of carbohydrates is C n (H 2 0) m.
All carbohydrates are divided into simple, or monosaccharides, and complex, or polysaccharides(Fig. 5). Of the monosaccharides, the most important for living organisms are ribose, deoxyribose, glucose, fructose, galactose.
Rice. 5. The structure of molecules of simple and complex carbohydrates
Di- And polysaccharides are formed by combining two or more monosaccharide molecules. So, sucrose(cane sugar), maltose(malt sugar), lactose(milk sugar) – disaccharides, formed as a result of the fusion of two monosaccharide molecules. Disaccharides are similar in properties to monosaccharides. For example, both horony are soluble in water and have a sweet taste.
Polysaccharides consist of large number monosaccharides. These include starch, glycogen, cellulose, chitin etc. (Fig. 6). With an increase in the number of monomers, the solubility of polysaccharides decreases and the sweet taste disappears.
The main function of carbohydrates is energy. During the breakdown and oxidation of carbohydrate molecules, energy is released (with the breakdown of 1 g of carbohydrates - 17.6 kJ), which ensures the vital functions of the body. When there is an excess of carbohydrates, they accumulate in the cell as reserve substances (starch, glycogen) and, if necessary, are used by the body as a source of energy. Increased breakdown of carbohydrates in cells can be observed, for example, during seed germination, intense muscle work, and prolonged fasting.
Carbohydrates are also used as building material. Thus, cellulose is an important structural component of the cell walls of many unicellular organisms, fungi and plants. Due to its special structure, cellulose is insoluble in water and has high strength. On average, 20-40% of the material in plant cell walls is cellulose, and cotton fibers are almost pure cellulose, which is why they are used to make textiles.
Rice. 6. Scheme of the structure of polysaccharides
Chitin is part of the cell walls of some protozoa and fungi; it is also found in certain groups of animals, such as arthropods, as an important component of their exoskeleton.
Complex polysaccharides are also known, consisting of two types of simple sugars, which regularly alternate in long chains. Such polysaccharides perform structural functions in the supporting tissues of animals. They are part of the intercellular substance of the skin, tendons, and cartilage, giving them strength and elasticity.
Some polysaccharides are part of cell membranes and serve as receptors, allowing cells to recognize each other and interact.
Carbohydrates, or saccharides. Monosaccharides. Disaccharides. Polysaccharides. Ribose. Deoxyribose. Glucose. Fructose. Galactose. Sucrose. Maltose. Lactose. Starch. Glycogen. Chitin
Questions
1. What composition and structure do carbohydrate molecules have?
2. What carbohydrates are called mono-, di- and polysaccharides?
3. What functions do carbohydrates perform in living organisms?
Tasks
Analyze Figure 6 “Structure diagram of polysaccharides” and the text of the paragraph. What assumptions can you make based on a comparison of the structural features of the molecules and the functions performed by starch, glycogen and cellulose in a living organism? Discuss this issue with your classmates.
§ 6. Lipids
1. What fat-like substances do you know?
2. What foods are rich in fat?
3. What is the role of fats in the body?
Lipids(from Greek lipos- fat) is a large group of fat-like substances that are insoluble in water. Most lipids consist of high molecular weight fatty acids and the trihydric alcohol glycerol (Fig. 7).
Lipids are present in all cells without exception, performing specific biological functions.
Fats- the simplest and most widespread lipids - play an important role as energy source. When oxidized, they provide more than twice as much energy as carbohydrates (38.9 kJ when breaking down 1 g of fat).
Rice. 7. Structure of the triglyceride molecule
Fats are the main form lipid storage in a cage. In vertebrates, approximately half of the energy consumed by cells at rest comes from fat oxidation. Fats can also be used as a source of water (the oxidation of 1 g of fat produces more than 1 g of water). This is especially valuable for arctic and desert animals living in conditions of scarcity of free water.
Due to their low thermal conductivity, lipids perform protective functions, i.e. they serve for thermal insulation of organisms. For example, many vertebrates have a well-defined subcutaneous fat layer, which allows them to live in cold climates, and in cetaceans it also plays another role - it promotes buoyancy.
Lipids perform and construction function, since their insolubility in water makes them essential components of cell membranes.
Many hormones(eg, adrenal cortex, gonads) are lipid derivatives. Therefore, lipids are characterized regulatory function.
Lipids. Fats. Hormones. Functions of lipids: energy, storage, protective, construction, regulatory
Questions
1. What substances are lipids?
2. What structure do most lipids have?
3. What functions do lipids perform?
4. Which cells and tissues are richest in lipids?
Tasks
After analyzing the text of the paragraph, explain why many animals before winter, and migratory fish before spawning, tend to accumulate more fat. Give examples of animals and plants in which this phenomenon is most pronounced. Is excess fat always good for the body? Discuss this problem in class.
§ 7. Composition and structure of proteins
1. What is the role of proteins in the body?
2. What foods are rich in proteins?
Among organic substances squirrels, or proteins, are the most numerous, most diverse and of paramount importance biopolymers. They account for 50–80% of the dry mass of the cell.
Protein molecules are large in size, which is why they are called macromolecules. In addition to carbon, oxygen, hydrogen and nitrogen, proteins may contain sulfur, phosphorus and iron. Proteins differ from each other in the number (from one hundred to several thousand), composition and sequence of monomers. Protein monomers are amino acids (Fig. 8).
An infinite variety of proteins is created by different combinations of just 20 amino acids. Each amino acid has its own name, special structure and properties. Their general formula can be represented in the following form:
An amino acid molecule consists of two parts identical to all amino acids, one of which is an amino group (-NH 2) with basic properties, the other is a carboxyl group (-COOH) with acidic properties. The part of the molecule called the radical (R) has a different structure for different amino acids. The presence of basic and acidic groups in one amino acid molecule determines their high reactivity. Through these groups, amino acids are combined to form proteins. In this case, a water molecule appears, and the released electrons form peptide bond. That's why proteins are called polypeptides.
Rice. 8. Examples of the structure of amino acids - monomers of protein molecules
Protein molecules can have different spatial configurations - protein structure, and in their structure there are four levels structural organization(Fig. 9).
The sequence of amino acids in a polypeptide chain is primary structure squirrel. It is unique to any protein and determines its shape, properties and functions.
Most proteins have a spiral shape as a result of the formation of hydrogen bonds between CO and NH groups of different amino acid residues of the polypeptide chain. Hydrogen bonds are weak, but together they provide a fairly strong structure. This spiral is secondary structure squirrel.
Tertiary structure– three-dimensional spatial “packaging” of a polypeptide chain. The result is a bizarre, but specific configuration for each protein - globule. The strength of the tertiary structure is ensured by the various bonds that arise between amino acid radicals.
Rice. 9. Scheme of the structure of a protein molecule: I, II, III, IV – primary, secondary, tertiary, quaternary structures
Quaternary structure not typical for all proteins. It arises as a result of the combination of several macromolecules with a tertiary structure into a complex complex. For example, human blood hemoglobin is a complex of four protein macromolecules (Fig. 10).
This complexity of the structure of protein molecules is associated with the diversity of functions inherent in these biopolymers.
Violation of the natural structure of a protein is called denaturation(Fig. 11). It can occur under the influence of temperature, chemical substances, radiant energy and other factors. With a weak impact, only the quaternary structure disintegrates, with a stronger impact, the tertiary, and then the secondary, and the protein remains in the form of a polypeptide chain.
Rice. 10. Scheme of the structure of the hemoglobin molecule
This process is partially reversible: if the primary structure is not destroyed, then the denatured protein is able to restore its structure. It follows that all structural features of a protein macromolecule are determined by its primary structure.
Except simple proteins, consisting only of amino acids, there are also complex proteins, which may include carbohydrates ( glycoproteins), fats ( lipoproteins), nucleic acids ( nucleoproteins) and etc.
The role of proteins in the life of a cell is enormous. Modern biology showed that the similarities and differences between organisms are ultimately determined by the set of proteins. The closer organisms are to each other in systematic position, the more similar their proteins are.
Rice. 11. Protein denaturation
Proteins, or proteins. Simple and complex proteins. Amino acids. Polypeptide. Primary, secondary, tertiary and quaternary structures of proteins
Questions
1. What substances are called proteins or proteins?
2. What is the primary structure of a protein?
3. How are secondary, tertiary and quaternary protein structures formed?
4. What is protein denaturation?
5. On what basis are proteins divided into simple and complex?
Tasks
You know that the white of a chicken egg consists mainly of proteins. Think about what explains the change in the protein structure of a boiled egg. Give other examples you know of where protein structure can change.
§ 8. Functions of proteins
1. What is the function of carbohydrates?
2. What functions of proteins do you know?
Proteins perform extremely important and diverse functions. This is possible largely due to the variety of forms and composition of the proteins themselves.
One of the most important functions of protein molecules is construction (plastic). Proteins are part of all cell membranes and cell organelles. The walls of blood vessels, cartilage, tendons, hair and nails consist predominantly of protein.
Of great importance catalytic, or enzymatic, protein function. Special proteins - enzymes are capable of accelerating biochemical reactions in cells tens and hundreds of millions of times. About a thousand enzymes are known. Each reaction is catalyzed by a specific enzyme. You will learn more about this below.
Motor function perform special contractile proteins. Thanks to them, cilia and flagella move in protozoa, chromosomes move during cell division, muscles contract in multicellular organisms, and other types of movement in living organisms are improved.
It is important transport function proteins. Thus, hemoglobin carries oxygen from the lungs to the cells of other tissues and organs. In muscles, in addition to hemoglobin, there is another gas transport protein - myoglobin. Serum proteins promote the transport of lipids and fatty acids, biologically diverse active substances. Transport proteins in the outer membrane of cells carry various substances from the environment into the cytoplasm.
Specific proteins perform protective function. They protect the body from invasion of foreign proteins and microorganisms and from damage. Thus, antibodies produced by lymphocytes block foreign proteins; fibrin and thrombin protect the body from blood loss.
Regulatory function inherent in proteins - hormones. They maintain constant concentrations of substances in the blood and cells, participate in growth, reproduction and other vital processes. For example, insulin regulates blood sugar.
Proteins also have signaling function. The cell membrane contains proteins that can change their tertiary structure in response to environmental factors. This is how signals are received from the external environment and information is transmitted into the cell.
Proteins can perform energy function, being one of the sources of energy in the cell. When 1 g of protein is completely broken down into final products, 17.6 kJ of energy is released. However, proteins are used extremely rarely as a source of energy. Amino acids released when protein molecules are broken down are used to build new proteins.
Functions of proteins: construction, motor, transport, protective, regulatory, signaling, energy, catalytic. Hormone. Enzyme
Questions
1. What explains the diversity of protein functions?
2. What functions of proteins do you know?
3. What role do hormone proteins play?
4. What function do enzyme proteins perform?
5. Why are proteins rarely used as a source of energy?
§ 9. Nucleic acids
1. What is the role of the nucleus in a cell?
2. What cell organelles are the transmission of hereditary characteristics associated with?
3. What substances are called acids?
Nucleic acids(from lat. nucleus– nucleus) were first discovered in the nuclei of leukocytes. Subsequently, it was found that nucleic acids are contained in all cells, not only in the nucleus, but also in the cytoplasm and various organelles.
There are two types of nucleic acids - deoxyribonucleic(abbreviated DNA) And ribonucleic(abbreviated RNA). The difference in names is explained by the fact that the DNA molecule contains a carbohydrate deoxyribose, and the RNA molecule is ribose.
Nucleic acids are biopolymers consisting of monomers - nucleotides. The nucleotide monomers of DNA and RNA have a similar structure.
Each nucleotide consists of three components connected by strong chemical bonds. This nitrogenous base, carbohydrate(ribose or deoxyribose) and phosphoric acid residue(Fig. 12).
Part DNA molecules There are four types of nitrogenous bases: adenine, guanine, cytosine or thymine. They determine the names of the corresponding nucleotides: adenyl (A), guanyl (G), cytidyl (C) and thymidyl (T) (Fig. 13).
Rice. 12. Scheme of the structure of nucleotides - DNA (A) and RNA (B) monomers
Each DNA strand is a polynucleotide consisting of several tens of thousands of nucleotides.
The DNA molecule has a complex structure. It consists of two helically twisted chains, which are connected to each other along their entire length by hydrogen bonds. This structure, characteristic only of DNA molecules, is called double helix.
Rice. 13. DNA nucleotides
Rice. 14. Complementary connection of nucleotides
When a DNA double helix is formed, the nitrogenous bases of one chain are arranged in a strictly defined order opposite the nitrogenous bases of the other. In this case, an important pattern is revealed: thymine of another chain is always located opposite the adenine of one chain, cytosine is always located opposite guanine, and vice versa. This is explained by the fact that the nucleotide pairs adenine and thymine, as well as guanine and cytosine, strictly correspond to each other and are complementary, or complementary(from lat. complementum- addition), each other. And the pattern itself is called principle of complementarity. In this case, two hydrogen bonds always arise between adenine and thymine, and three between guanine and cytosine (Fig. 14).
Consequently, in any organism the number of adenyl nucleotides is equal to the number of thymidyl nucleotides, and the number of guanyl nucleotides is equal to the number of cytidyl nucleotides. Knowing the sequence of nucleotides in one DNA chain, the principle of complementarity can be used to establish the order of nucleotides in another chain.
With the help of four types of nucleotides, DNA records all the information about the body, which is passed on to subsequent generations. In other words, DNA is the carrier of hereditary information.
DNA molecules are mainly found in the nuclei of cells, but small amounts are found in mitochondria and plastids.
An RNA molecule, unlike a DNA molecule, is a polymer consisting of a single chain of much smaller dimensions.
RNA monomers are nucleotides consisting of ribose, a phosphoric acid residue and one of four nitrogenous bases. Three nitrogenous bases - adenine, guanine and cytosine - are the same as those of DNA, and the fourth - uracil.
The formation of an RNA polymer occurs through covalent bonds between ribose and the phosphoric acid residue of neighboring nucleotides.
There are three types of RNA, differing in structure, molecular size, location in the cell and functions performed.
Ribosomal RNA (rRNA) are part of ribosomes and participate in the formation of their active centers, where the process of protein biosynthesis occurs.
Transfer RNAs (tRNA) - the smallest in size - transport amino acids to the site of protein synthesis.
Information, or template, RNA (mRNA) are synthesized on a section of one of the chains of the DNA molecule and transmit information about the structure of the protein from the cell nucleus to the ribosomes, where this information is implemented.
Thus, different types of RNA represent a single functional system aimed at implementing hereditary information through protein synthesis.
RNA molecules are found in the nucleus, cytoplasm, ribosomes, mitochondria and plastids of the cell.
Nucleic acid. Deoxyribonucleic acid, or DNA. Ribonucleic acid, or RNA. Nitrogen bases: adenine, guanine, cytosine, thymine, uracil, nucleotide. Double helix. Complementarity. Transfer RNA (tRNA). Ribosomal RNA (rRNA). Messenger RNA (mRNA)
Questions
1. What is the structure of a nucleotide?
2. What is the structure of the DNA molecule?
3. What is the principle of complementarity?
4. What are the similarities and differences in the structure of DNA and RNA molecules?
5. What types of RNA molecules do you know? What are their functions?
Tasks
1. Outline your paragraph.
2. Scientists have found that a fragment of a DNA chain has the following composition: C-G G A A A T T C C. Using the principle of complementarity, complete the second chain.
3. During the study, it was found that in the DNA molecule under study, adenines account for 26% of total number nitrogenous bases. Count the number of other nitrogenous bases in this molecule.
Look at the root!
Kozma Prutkov
What chemical elements make up a living cell? What role do sugars and lipids play? How are proteins structured and how do their molecules acquire a certain spatial shape? What are enzymes and how do they recognize their substrates? What is the structure of RNA and DNA molecules? What features of the DNA molecule allow it to play the role of a carrier of genetic information?
Lesson-lecture
ELEMENTARY AND MOLECULAR COMPOSITION OF LIVING THINGS. We begin our acquaintance with living systems from the molecular genetic level. This is the level of molecules that form the structural and functional basis of the cells of living organisms.
Retrovirus. Viruses demonstrate amazing geometric shapes!
Let us remember that of all the known elements included in Periodic table D.I. Mendeleev, about 80 were found in a living cell. Moreover, among them there is not a single one that would be absent in inanimate nature. This serves as one of the proofs of the commonality of living and inanimate nature.
More than 90% of a cell's mass is made up of carbon, hydrogen, nitrogen and oxygen. Sulfur, phosphorus, potassium, sodium, calcium, magnesium, iron and chlorine are found in much smaller quantities in the cell. All other elements (zinc, copper, iodine, fluorine, cobalt, manganese, etc.) together make up no more than 0.02% of the cell mass. That's why they are called microelements. Microelements are part of hormones, enzymes and vitamins, i.e. compounds with high biological activity.
For example, a lack of iodine in the body, necessary for the production of the thyroid hormone - thyroxine, leads to a decrease in the production of this hormone and, as a consequence, to the development of serious diseases, including cretinism.
Most of the cell contents are water. Many substances enter or leave the cell in the form of aqueous solutions; most intracellular reactions also occur in an aqueous environment. Moreover, water is directly involved in a number of chemical reactions, donating H + or OH - ions to the resulting compounds. Due to its high heat capacity, water stabilizes the temperature inside the cell, making it less dependent on temperature fluctuations in the environment surrounding the cell.
In addition to water, which makes up 70% of the cell volume, it also contains organic substances - carbon compounds. Among them there are small molecules containing up to 30 carbon atoms and macromolecules. The former include simple sugars (monosaccharides), lipids, amino acids and nucleotides. They serve as structural components for the construction of macromolecules, and in addition, they play a significant role in the metabolic processes and energy of a living cell.
And yet, the basis of life at the molecular level is proteins and nucleic acids, which we will discuss in more detail.
AMINO ACIDS AND PROTEINS. Squirrels have a special role in living nature. They serve as the building material of the cell, and almost none of the processes that occur in cells can occur without their participation.
A protein molecule is a chain of amino acids, and the number of links in such a chain can range from tens to several thousand. Adjacent amino acids are linked to each other special type chemical bond, which is called peptide. This bond is formed during the process of protein synthesis, when the carboxyl group of one amino acid binds to the adjacent amino group of another amino acid (Fig. 32).
Rice. 32. Peptide bond
All 20 types of amino acids are involved in the construction of proteins. However, the order of their alternation in the protein chain is very different, which creates the opportunity for a huge number of combinations, and, consequently, for the construction of numerous types of protein molecules. It should be noted that only plants are able to synthesize all 20 amino acids necessary to build proteins. Animals obtain a number of amino acids, called essential amino acids, by eating plants.
The sequence of amino acids in a protein molecule is denoted as primary structure squirrel (Fig. 33). There are also secondary structure protein, which is understood as the nature of the spatial arrangement of individual fragments of the amino acid chain. In the secondary structure, sections of the protein molecule are shaped like helices or folded layers. In their formation, an important role is played by hydrogen bonds established between oxygen and hydrogen of peptide bonds (-N-H...0=C-) of different amino acids.
Rice. 33. Protein structure
Under tertiary structure protein refers to the spatial arrangement of the entire amino acid chain.
Tertiary structure has a direct bearing on the shape of the protein molecule, which can be thread-like or round. In the latter case, the molecule is folded in such a way that its hydrophobic regions are inside, and its polar hydrophilic groups are on the surface. The resulting spatial structure is called globule.
Finally, some proteins may contain several globules, each of which is formed by an independent chain of amino acids. The combination of several globules into a single complex is designated by the term quaternary structure squirrel. For example, the hemoglobin protein molecule consists of four globules containing a non-protein part - heme.
A protein molecule is capable of self-organizing into a complex spatial structure, the configuration of which is specific and determined by the sequence of amino acids, i.e., the primary structure of the protein.
Self-organization is one of the unique properties proteins, which underlies many of the functions they perform. In particular, the mechanism of recognition by enzymes (biological catalysts) of its own is based on the specificity of the spatial structure of the protein molecule. substrate, i.e. a molecule that, after interacting with an enzyme, undergoes certain chemical transformations and turns into product.
Enzymes are proteins, a certain part of the molecule of which forms the active center. It binds a substrate specific to a given enzyme and converts it into a product. In this case, the enzyme is able to distinguish its substrate due to the special spatial configuration of the active center, specific to each enzyme. You can imagine that the substrate fits the enzyme like a key to a lock.
You are convinced that all the properties of a protein are based on its primary structure - the sequence of amino acids in the molecule. It can be compared to a word that is written in an alphabet consisting of 20 amino acid letters. And if there are words, then there may be a cipher with which these words can be encoded. How? Familiarity with the structure of nucleic acids will help answer this question.
NUCLEOTIDES AND NUCLEIC ACIDS. Nucleotides consist of a nitrogen-containing cyclic compound (nitrogen base), a five-carbon sugar, and a phosphoric acid residue. Nucleic acid macromolecules are built from them.
The composition of molecules RNA(ribonucleic acid) includes nucleotides built on the sugar ribose and containing adenine (A), guanine (G), cytosine (C) and uracil (U) as nitrogenous bases. Nucleotides that make up a molecule DNA(deoxyribonucleic acid), contain deoxyribose, and instead of uracil - thymine (T).
The linkage of nucleotides to each other in a DNA (RNA) molecule occurs due to the connection of the phosphorus residue of one nucleotide with the deoxyribose (ribose) of another (Fig. 34).
Rice. 34. Chain composition and structure of the DNA molecule
In the course of studies of the composition of DNA molecules, it was found that in each of them the number of adenine nitrogenous bases (A) is equal to the number of thymine (T), and the number of guanine (G) is equal to the number of cytosine (C). This discovery served as a prerequisite for the creation by J. Watson and F. Crick in 1953 of a model of the DNA molecule - the famous double helix.
According to this model, the DNA molecule consists of two chains that are folded into a right-handed spiral (Fig. 35).
Rice. 35. DNA structure model
Each chain contains a sequence of nucleotides that strictly corresponds (complementary) to the sequence of the other chain. This correspondence is achieved by the presence of hydrogen bonds between the nitrogenous bases of two chains directed towards each other - A and T or G and C.
Communication between other pairs of nitrogenous bases is impossible, since the spatial structure of the molecules of nitrogenous bases is such that only A and T, as well as G and C, can come close to each other enough to form hydrogen bonds with each other.
The most important feature of DNA is the possibility of its self-duplication - replication, which is carried out with the participation of a group of enzymes (Fig. 36).
Rice. 36. DNA replication scheme
In certain areas, including at one of the ends, of a double-stranded helical DNA molecule, hydrogen bonds between the chains are broken. They separate and unwind.
This process gradually takes over the entire molecule. As the chains of the parent molecule diverge on them, as on a matrix, from those available in environment nucleotides, daughter chains are built. The assembly of a new chain proceeds in strict accordance with the principle of complementarity: against each A there is a T, against G - C, etc. As a result, two new DNA molecules are obtained, each of which has one chain left from the original DNA molecule, and the second is a new one . In this case, the two DNA molecules formed during replication are identical to the original one.
The ability of the DNA molecule to self-copy is the basis for the transmission of hereditary information by living organisms. The sequence of nucleotide bases in a DNA molecule serves as the code that encodes information about the proteins necessary for the functioning of the body.
Unlike DNA, an RNA molecule consists of a single polynucleotide chain. There are several types of RNA that perform different functions in the cell. An RNA copy of a section of a DNA chain is called information or messenger RNA(mRNA) and plays the role of an intermediary in the transfer of genetic information from DNA to cell structures that synthesize protein - ribosomes. In addition, the cell contains ribosomal RNA(rRNA), which together with proteins form ribosomes, transfer RNAs(tRNA), transporting amino acids to the site of protein synthesis, and some others.
The DNA molecule consists of two complementary strands of nucleotides coiled into a spiral, which are held together by hydrogen bonds. forming A-T And G-C pairs grounds. The nucleotide sequence of a DNA chain serves as a code that encodes genetic information. Deciphering of this information is carried out with the participation of RNA molecules. The ability of DNA to self-copy (replicate) provides the possibility of transmitting genetic information in living nature.
- Why are proteins called molecules of life?
- What is the role spatial structures proteins in cell life processes?
- What principle underlies DNA replication processes?
Question 1. What processes do scientists study at the molecular level?
At the molecular level, the most important processes of the body's life are studied: its growth and development, metabolism and energy conversion, storage and transmission of hereditary information, variability. Elementary unit at the molecular level, a gene serves as a fragment of a nucleic acid molecule, in which a certain amount of biological information is recorded in a qualitative and quantitative sense.
Question 2. What elements predominate in the composition of living organisms?
A living organism contains more than 70-80 chemical elements, but carbon, oxygen, hydrogen, nitrogen and phosphorus predominate.
Question 3. Why are molecules of proteins, nucleic acids, carbohydrates and lipids considered as biopolymers only in the cell?
Molecules of proteins, nucleic acids, carbohydrates and lipids are polymers because they consist of repeating monomers. But only in a living system (cell, organism) do these substances manifest their biological essence, possessing a number of specific properties and performing many important functions. Therefore, in living systems such substances are called biopolymers. Outside a living system, these substances lose their biological properties and are not biopolymers.
Question 4. What is meant by the universality of biopolymer molecules?
Regardless of the level of complexity and functions performed in the cell, all biopolymers have the following features:
their molecules have few long branches, but many short ones;
polymer chains are strong and do not spontaneously break apart;
capable of carrying a variety of functional groups and molecular fragments that provide biochemical functional activity, i.e., the ability to carry out biochemical reactions and transformations necessary for the cell in the intracellular solution environment;
have flexibility sufficient to form very complex spatial structures necessary to perform biochemical functions, i.e., for the operation of proteins as molecular machines, nucleic acids as programming molecules, etc.;
The C-H and C-C bonds of biopolymers, despite their strength, are also batteries of electronic energy.
The main property of biopolymers is the linearity of polymer chains, since only linear structures are easily encoded and “assembled” from monomers. In addition, if the polymer thread is flexible, then it is quite easy to form the desired spatial structure from it, and after the molecular machine constructed in this way is depreciated and breaks, it can be easily disassembled into its component elements in order to use them again. The combination of these properties is found only in carbon-based polymers. All biopolymers in living systems are capable of performing certain properties and perform many essential functions. The properties of biopolymers depend on the number, composition and order of arrangement of their constituent monomers. The ability to change the composition and sequence of monomers in the polymer structure allows the existence of a huge variety of biopolymer options, regardless of the species of the organism. In all living organisms, biopolymers are built according to a single plan.
What elements predominate in living organisms?
Why are molecules of proteins, nucleic acids, carbohydrates and lipids considered as biopolymers only in the cell?
What is meant by the word universality of biopolymer molecules?
a) sequence of alternation of amino acids
b) the number of amino acids in the molecule
c) the form of the tertiary structure
d) all the specified features
3. In what case is the composition of a DNA nucleotide correctly indicated?
a) ribose, phosphoric acid residue, thymine
b) phosphoric acid, uracil, deoxyribose
c) phosphoric acid residue, deoxyribose, adenine
d) phosphoric acid, ribose, guanine
4. Monomers of nucleic acids are:
a) nitrogenous bases
b) ribose or deoxyribose
c) deoxyribose and phosphate groups
d) nucleotides
5. Amino acids in a protein molecule are connected through:
a) ionic bond
b) peptide bond
c) hydrogen bond
6. What is the function of transfer RNA?
a) transfers amino acids to ribosomes
b) transfers information from DNA
c) forms ribosomes
d) all listed functions
7. Enzymes are biocatalysts consisting of:
a) proteins b) nucleotides c) lipids c) fats
8. Polysaccharides include:
a) starch, ribose
b) glycogen, glucose
c) cellulose, starch
d) starch, sucrose
9. Carbon as an element is included in:
a) proteins and carbohydrates
b) carbohydrates and lipids
c) carbohydrates and nucleic acids
d) all organic compounds of the cell
10. The cell contains DNA:
a) in the nucleus and mitochondria
b) in the nucleus, cytoplasm and various organelles
c) in the nucleus, mitochondria and cytoplasm
d) in the nucleus, mitochondria, chloroplasts
WHAT IS A NUCLEIC ACIDS MONOMETER? OPTIONS (AMINO ACID, NUCLEOTIDE, PROTEIN MOLECULE?) WHAT IS INCLUDEDNUCLEOTIDE COMPOSITION
OPTIONS: (AMINO ACID, NITROGEN BASE, PHOSPHORIC ACID RESIDUE, CARBOHYDRATE?)
Help me please!1.The science that studies cells is called:
A) Genetics;
B) Selection;
B) ecology;
B) Cytology.
2. Organic substances of the cell:
A) Water, minerals, fats;
B) Carbohydrates, lipids, proteins, nucleic acids;
C) Carbohydrates, minerals, fats;
D) Water, minerals, proteins.
3. Of all organic substances, the bulk of the cell consists of:
A) Proteins.
B) Carbohydrates
B) Fats
D) Water.
4. Replace the highlighted words with one word:
A) Small molecules of organic substances form complex molecules in the cell.
B) The permanent structural components of the cell perform vital functions for the cell.
C) The highly ordered, semi-liquid internal environment of the cell ensures the chemical interaction of all cellular structures.
D) The main photosynthetic pigment gives the green color to chloroplasts.
5. Accumulation and packaging chemical compounds in the cage they carry out:
A) Mitochondria;
B) Ribosomes;
B) Lysosomes;
D) Golgi complex.
6. The functions of intracellular digestion are performed by:
A) Mitochondria;
B) Ribosomes;
B) Lysosomes;
D) Golgi complex.
7. The “assembly” of a polymeric protein molecule is carried out:
A) Mitochondria;
B) Ribosomes;
B) Lysosomes;
D) Golgi complex.
8. The set of chemical reactions resulting in the breakdown of organic substances and the release of energy is called:
A) Catabolism;
B) anabolism;
B) Metabolism;
D) Assimilation
9. “Copying” genetic information from a DNA molecule by creating mRNA is called:
A) Broadcast;
B) Transcription;
B) Biosynthesis;
D) Glycolysis.
10. The process of formation of organic substances in light in chloroplasts using water and carbon dioxide is called:
A) Photosynthesis;
B) Transcription;
B) Biosynthesis;
D) Glycolysis.
11. The enzymatic and oxygen-free process of decomposition of organic substances is called:
A) Photosynthesis;
B) Transcription;
B) Biosynthesis;
D) Glycolysis.
12. Name the main provisions of the cell theory.
Loading...