Which amino acid is aromatic
B) aspartic acid
C) cysteine
D) tryptophan +
E) histidine
109. What amino acid is heterocyclic:
A) histidine +
Which amino acid exhibits basic properties
B) aspartic acid
D) phenylalanine
111. Specify the zwitterrion of the amino acid:
b) 
c) 
D) 
+
e) 
112. What is the peptide bond:
A) 
113. Amino acid, in the molecule of which there is no asymmetric carbon atom:
A) tyrosine
C) glycine +
D) phenylalanine
What amino acid contains sulfur?
A) arginine
B) tryptophan
C) histidine
D) cysteine +
115. Amino acid, in the molecule of which there is no free amino group:
A) proline +
B) cysteine
C) glutamic acid
D) tryptophan
E) phenylalanine
116. If the pH of an amino acid solution is equal to the value of the isoelectric point, then:
A) the amino acid molecule is negatively charged
B) the amino acid molecule is positively charged
C) the amino acid molecule is neutral +
D) the amino acid is highly soluble in water
E) the amino acid molecule is easily destroyed
117. If the pH of an amino acid solution is equal to the value of the isoelectric point, then:
A) an amino acid molecule in the form of a bipolar ion +
B) an amino acid molecule in the form of an anion
C) an amino acid molecule in the form of a cation
D) the amino acid molecule is not charged
E) the amino acid molecule is destroyed
118. The following is not found in a protein molecule:
A) creatine phosphate +
B) glutamine
D) histidine
E) tyrosine
119. glycine = 2.4, pK2 glycine \u003d 9.7, the isoelectric point of glycine is:
120. A protein molecule contains:
A) carboxylic acid
B) D--amino acids
C) D--amino acids
D) L--amino acids
E) L- -amino acids +
121. An amino acid that is not found in the composition of a protein molecule:
A) tryptophan
B) aspartic acid
D) ornithine +
E) histidine
122. Non-essential amino acids do not include:
C) glutamic acid
D) tryptophan +
123. Essential amino acids do not include:
B) phenylalanine
D) proline +
E) threonine
124. Non-essential amino acids include:
B) isoleucine
C) aspartic acid +
D) methionine
E) tryptophan
125. Essential amino acids include:
B) glutamic acid
D) asparagine
E) cysteine
126. Ninhydrin reaction - a qualitative reaction to:
A) free amino groups +
B) free carboxyl groups
C) for determination of hydroxyl groups
D) to determine SH-groups
E) to determine aromatic amino acids
127. To determine the protein in a solution, use:
A) Selivanov reaction
B) biuret reaction +
C) Sakaguchi reaction
D) nitroprusside reaction
E) Millon reaction
128. Millon's reaction is used: to determine:
A) tyrosine residues in a protein molecule +
B) guanidine group of arginine
C) imidazole group of histidine
D) aromatic amino acids
E) SH-groups of cysteine
129. What amino acid is dicarboxylic:
A) tyrosine
B) glutamic acid +
D) tryptophan
130. In the composition of a hemoglobin molecule:
A) 1 subunit
B) 3 subunits
C) 6 subunits
D) 4 subunits +
E) 2 subunits
131. How many subunits are in albumin molecule:
132. If the pH of the protein solution is higher than the value of the isoelectric point of the protein molecule, then:
A) the protein molecule is negatively charged +
B) the protein molecule is positively charged
C) the protein molecule is uncharged
D) the protein molecule is denatured
E) protein is insoluble
133. Globular proteins do not include:
A) trypsin
B) hemoglobin
C) keratin +
D) albumin
E) myoglobin
134. Fibrillar proteins do not include:
A) collagen
B) insulin +
C) keratin
E) elastin
135. The composition of glycoproteins includes:
A) phosphates
B) carbohydrates +
E) metal ions
136. Protein molecule at the isoelectric point:
A) negatively charged
B) positively charged
C) the total charge is zero +
D) denatured
E) soluble in solution
137. Enzymatic activation of amino acids requires:
138. Hemoglobin contains:
A) manganese
B) molybdenum
E) iron +
139. The prosthetic group of myoglobin is:
B) molybdenum
C) magnesium ions
D) copper ions
E) thiamine pyrophosphate
140. Bonds are involved in the formation of the tertiary structure of a protein molecule:
A) covalent bonds
B) hydrogen bonds
C) hydrophobic interactions
D) ionic interactions
E) all the above links +
141. Protein with a quaternary structure:
A) hemoglobin +
B) ribonuclease
C) albumin
D) myoglobin
E) insulin
142. Carrier of molecular oxygen in the body:
A) amylase
B) albumin
C) hemoglobin +
E) collagen
143. The composition of phosphoproteins includes:
B) phosphates +
C) carbohydrates
E) metal ions
144. Protective function in the body is performed by:
A) immunoglobulins +
B) albumin
C) histones
D) phosphatases
145. The function that proteins perform in the body:
A) transport
B) protective
C) regulatory
D) structural
E) all specified functions +
146. Lipoprotein is a protein containing in its composition:
B) metal ions
C) carbohydrates
D) lipids +
E) phosphates
147. Nucleoproteins are:
A) complex proteins, which include lipids
B) complexes of nucleic acids with proteins +
C) complex proteins, which include carbohydrates
D) complex proteins, which include phosphates
E) complex proteins, which include metal ions
148. For the activity of pepsin:
A) pH of the medium should be equal to pH 1.5-3.0 +
B) the medium must be neutral
C) the medium must be alkaline
D) metal ions must be present in the medium
E) free amino acids must be present in the medium
149. Blood protein that binds fatty acids:
A) hemoglobin
B) albumin +
C) orosomucoid
D) haptoglobin
E) immunoglobulin
150. During the reaction of transamination of amino acids, the following are formed:
A) -keto acids +
B) aldehydes
D) unsaturated hydrocarbons
E) hydroxy acids
151. Buffer properties of amino acids are due to:
A) the presence of a carboxyl group
B) the presence of an amino group
C) good solubility
D) the nature of the radical
E) the presence in the molecule of both carboxyl and amino groups +
152. Tyrosine is formed in the liver from:
A) tryptophan
B) phenylalanine +
D) histidine
E) arginine
153. Amino acids are used in the body:
A) for protein synthesis
B) for the synthesis of hormones
C) for the formation of -keto acids
D) as a source of nitrogen for the synthesis of nitrogenous compounds of non-amino acid nature
E) in all specified cases +
154. In the urea cycle is formed:
B) isoleucine
C) histidine
D) arginine +
E) tryptophan
155. Enzymes in the body:
A) catalyze the rate of a chemical reaction +
B) perform a structural function
C) reserve fund of chemical energy for anabolic reactions
D) perform a protective function
E) regulate osmotic pressure
156. Redox reactions are catalyzed by:
A) oxidoreductase +
C) hydrolases
D) transferase
157. Enzymes that catalyze the transfer of atoms and atomic groups:
B) transferases +
C) oxidoreductase
D) hydrolases
158. Enzymes that catalyze the hydrolysis of chemical bonds:
A) oxidoreductase
B) transferase
D) hydrolases +
159. Enzymes catalyzing isomerization reactions:
A) oxidoreductase
B) transferase
C) isomerase +
D) hydrolases
160. Enzymes that catalyze the reactions of formation of a new bond:
A) ligases +
B) hydrolases
C) transferase
D) isomerases
E) oxidoreductase
161. Enzymes that catalyze the reactions of non-hydrolytic cleavage and the formation of a double bond:
A) hydrolases
B) transferase
C) isomerases
D) oxidoreductase
162. The class of hydrolases includes:
A) esterases
B) proteinases
C) glycosidases
E) all the indicated classes of enzymes +
163. Oxidoreductases do not include:
A) lactate dehydrogenase
B) alcohol dehydrogenase
C) peroxidase
D) cytochrome oxidase
E) ribonuclease +
164. Apoenzyme is:
A) prosthetic group
B) protein associated with the prosthetic group +
C) the protein part of an enzyme, the active form of which contains a coenzyme
D) organic cofactors of the enzyme
E) simple protein
165. Nicotinamide adenine dinucleotide - a coenzyme that carries:
A) methyl groups
B) alkyl groups
C) acyl groups
D) amine groups
E) hydrogen atoms +
166. Does not apply to coenzymes:
A) flavin mononucleotide
B) pyridoxal phosphate
C) thyroxine +
D) nicotinamide adenine dinucleotide
E) thiamine pyrophosphate
167. Coenzyme that transfers acyl groups:
A) nicotinamide adenine dinucleotide
B) pyridoxal phosphate
C) flavin mononucleotide
D) coenzyme A +
E) folic acid
168. The properties of enzymes do not include:
A) does not reduce the activation energy of chemical reactions +
B) effectiveness of action
C) high specificity towards the substrate
D) lowers the activation energy of a chemical reaction
E) specificity of action relative to the type of chemical reaction
169. Hydrolysis of esters is catalyzed by:
A) esterases +
B) glycosidases
C) hydrolases
D) proteinases
E) synthetase
170. Coenzymes include:
A) tetrahydrofolic acid
B) thiamine pyrophosphate
C) flavin adenine dinucleotide
D) lipoamide
E) all specified compounds +
171. Does not apply to proteolytic enzymes:
A) trypsin
B) lipase +
D) elastase
E) chymotrypsin
172. Proteolytic enzymes catalyze:
A) hydrolysis of the peptide bond +
B) hydrolysis of the glycosidic bond
C) ester bond hydrolysis
D) hydrolysis of the phosphoester bond
E) hydrolysis of an ether bond
173. Enzymes are:
A) biological catalysts that speed up chemical reactions +
B) the main building material of cell membranes
C) substances that provide detoxification of the body
D) inhibitors of chemical reactions
E) substances involved in the transmission of signal information
174. Competitive inhibitors:
A) bind to substrates
B) bind to the active site of the enzyme +
C) do not bind to the enzyme-substrate complex
D) do not bind to the active site of the enzyme, bind to another site of the enzyme
E) bind to the allosteric center of the enzyme irreversibly
175. Noncompetitive inhibitors:
A) are similar in structure to the substrate
B) differ in their structure from the substrate +
C) bind to the active site of the enzyme
D) denature the enzyme
E) bind to the substrate
176. Proteolytic enzyme pepsin:
A) functions in gastric juice at pH 1.5-3.0 +
B) functions in gastric juice at pH 9.0-11.0
C) part of the intestinal mucosa
D) functions in the small intestine
E) provides hydrolysis of triacylglycerides in adipose tissue
177. Trypsin is synthesized as a precursor in:
B) pancreas +
C) small intestine
D) adipose tissue
E) gastric mucosa
178. The activity of enzymes is associated with:
A) ambient temperature
B) medium pH
C) the presence in the environment of various chemical compounds
D) the nature of the substrate
E) with all specified conditions +
179. Enzymes accelerate the course of chemical reactions, because:
A) reduce the activation energy of a chemical reaction +
B) increase the activation energy of the reaction
C) reduce the concentration of the reaction product
D) change the structure of the substrate
E) change the concentration of the starting substances
180. The composition of nucleotides does not include:
A) phosphoric acid residue
B) pyrimidine bases
C) purine bases
D) deoxyribose
E) glucose +
181. The composition of ribonucleosides includes:
B) nitrogenous base and ribose +
E) phosphoric acid residue and ribose
182. DNA does not include:
B) uracil +
E) cytosine
183. The composition of RNA includes:
A) 2-D-deoxyribofuranose
B) glucopyranose
C) D-ribofuranose +
D) fructofuranose
E) arabinose
184. Nucleotide is:
A) adenosine
C) adenylic acid +
E) cytosine
185. The composition of deoxyribonucleotides includes:
A) a phosphoric acid residue and a nitrogenous base
B) nitrogenous base and ribose
C) nitrogenous base and deoxyribose
D) a residue of phosphoric acid and deoxyribose
E) phosphoric acid residue, deoxyribose and nitrogenous base +
186. Nitrogenous base, which is not part of RNA:
E) cytosine
187. DNA contains:
A) galactopyranose
B) glucopyranose
C) D-ribofuranose
D) fructofuranose
E) 2-D-deoxyribofuranose +
188. Nucleoside is not:
A) guanosine
B) ribose-5-phosphate +
C) adenosine
E) cytidine
189. Monomeric units of nucleic acids are:
A) nucleotides +
B) nitrogenous bases
C) amino acids
D) ribose phosphates
E) monosaccharides
190. In nucleic acid molecules, nucleotides are linked:
A) disulfide bonds
Introduction……………………………………………………………………………………………..
Nutritional assessment………………………………………………………………………..
Sulfur………………………………………………………………………………………………………
Protein amino acids……………………………………………………………………………
Enrichment of diets with sulfur………………………………………………………………
The influence of sulfur on the furs of animals………………………………………………………..
Introduction
The creation of a solid food base is not only an increase in the production and improvement of the quality of various types of feed, but, above all, the introduction of highly efficient methods and means of their production, preparation, which contribute to the high digestibility of nutrients contained in feed by animals and ensure their rational use.
Feeding affects the development, growth rate, body weight and reproductive functions of the animal. Livestock breeding can be successfully developed only if livestock and poultry are fully provided with high-quality fodder. Of all environmental factors, feeding has the greatest impact on productivity. In the cost structure of livestock products, the share of feed is 50-55% for milk production, 65-70% for beef, and 70-75% for pork.
In modern animal husbandry, much attention is paid to ensuring a balanced diet for animals. By applying scientifically based feeding systems, animal productivity can be increased and feed can be used efficiently. In the process of nutrition, the constituent substances act on the animal's body not in isolation from each other, but in a complex. The balance of feed ingredients in accordance with the needs of animals is the main indicator of this complex.
Nutritional assessment
For animal husbandry, it is important not only the quantity, but mainly the quality of feed, i.e. their value is determined by the content of nutrients. Such rations and feeds are considered complete, which contain all the substances necessary for the animal's body and are capable of ensuring the normal functioning of all its physiological functions for a long time.
Nutritional value is understood as the property of feed to satisfy the natural needs of animals for food. It is possible to determine the nutritional value of the feed only in the process of its interaction with the body by the physiological state of the animal and the change in its productivity. The nutritional value of food cannot be expressed in any one indicator. The studies carried out by scientists on the role of individual nutrients in the life of the animal's body led to the conclusion that a comprehensive system for assessing the nutritional value of feed is needed. This assessment is made up of the following data: the chemical composition of the feed and its calorie content; nutrient digestibility; general (energy) nutritional value; protein, mineral and vitamin nutrition.
To assess the nutritional value of feed, it is necessary to know their chemical composition and the main processes that occur during the conversion of feed nutrients into livestock products. The method of assessing the nutritional value of feed by digestible nutrients has its drawbacks, since digestion of feed is the assimilation of only a part of the nutrients of the feed of the animal and the first stage of metabolism between the body and the environment. Not all digestible nutrients are equally used by the body for life and production. For example: wheat bran and barley grain have almost the same amount of nutrients (60–62%), but the productive effect of bran is about 25% lower than that of barley. In addition, one part, considered digestible, is actually destroyed by microorganisms with the formation of carbon dioxide, methane and organic acids, the other part is excreted from the body with fluids in the form of urea and heat. Thus, for a more complete assessment of the nutritional value of feeds and diets, it is necessary to know the final results of feeding, i.e. what part of the digestible nutrients of each feed is absorbed by the body and converted into constituent parts of the animal's body or into products obtained from the animal. Therefore, along with the assessment of digestible nutrients, an assessment of the total nutritional value (calorie content) is used.
Sulfur
Sulfur is vital for the animal organism. In the body of animals it is found mainly in the form of complex organic compounds - protein amino acids. In the body of animals, sulfur is 0.12-0.15%, most of it is concentrated in the hairline, horn shoe, and skin. Sulfur is also part of insulin (pancreatic hormone) and thiamine (vitamin B1).
Relatively a lot of sulfur in grain cereals and legumes, meadow and alfalfa hay, reverse. All foods rich in protein contain more sulfur than those poor in it.
The need for sulfur in sheep and livestock is 0.25-0.4% of the dry matter of the feed ration. For example, a dairy cow needs 25-50 g of sulfur per day, depending on the daily milk yield, calves up to 6 months - 3-10, young animals - 13-25, depending on live weight and growth; sheep: adults - 3-9, lambs - 2-3 g per day. The need for sulfur in sheep depends mainly on the shearing of wool.
Sulfur improves the digestion of cellulose and supports the biosynthesis of B vitamins. Symptoms of an insufficient amount of sulfur in the body are loss of appetite, loss of part of the hairline and dull eyes. Many animal feeds can serve as a source of sulfur, for example, milk in various forms, etc.
It carries out its physiological role in the body through amino acids - cystine, methionine, taurine, glutathione, thiamine, which include.
protein amino acids
cystine
Important amino acid containing sulfur. It is a powerful antioxidant that the liver uses to neutralize damaging free radicals.
Strengthens connective tissues and enhances antioxidant processes in the body.
Promotes healing processes, stimulates the activity of white blood cells, helps to reduce pain during inflammation.
Essential acid for skin and hair.
Needed to protect against chemical toxins.
Methionine
One of the essential amino acids containing sulfur. Important for many bodily functions, including the production of immune cells and the functioning of the nervous system. It is a powerful antioxidant and is important for maintaining a healthy liver.
Precursor of cystine and creatine.
May increase antioxidant (glutathione) levels and lower cholesterol.
Helps detoxify and regenerate liver and kidney tissue.
methionine prevents skin diseases.
useful in some cases of allergy as it reduces the release of histamine.
Taurine
One of the most important, beneficial and safe amino acid supplements is taurine, widely known for its beneficial effects on the cardiovascular system. The body can produce taurine from cysteine with the help of vitamin B6.
Helps the absorption and destruction of fats.
Taurine, which is present in the organs of the central nervous system, retina, skeletal muscle and heart muscle, is useful in the treatment of cardiovascular diseases and some eye diseases.
Taurine functions in electrically active tissues such as the brain and heart and helps stabilize cell membranes.
There is an opinion that this amino acid has some antioxidant and cleansing effect.
With the help of zinc, taurine promotes the circulation of certain minerals into and out of cells and thus participates in the production of nerve impulses.
Glutathione
Glutathione is not a protein-building amino acid, it is a mixture of amino acid chains.
Glutathione forms enzymes such as glutathione peroxidase.
It is essential for life and is present in all cells of plants and animals.
Included in nutritional formulas as well as supplements that have a cleansing effect on the body, removing certain toxins
Thiamine (B1)
Synonyms: aneuril, aneurin, bevemin, benerva, berin, betaxin, betiamin, bitevan, oryzanin, etc.
Participates in carbohydrate metabolism, regulates the functions of the nervous system, cardiac activity. Absorption of the vitamin occurs in the intestine, and in tissue cells it is converted to cocarboxylase.
Protects cell membranes from the toxic effects of peroxidation products.
Not all pets need vitamin B1. In ruminants, thiamine is produced by certain bacteria that live in the rumen. However, poultry, rabbits, pigs and horses are quite susceptible to a lack of this vitamin.
And those animals that do not receive and do not produce vitamin B1 on their own often develop polyneuritis. With polyneuritis, as a rule, there is a disorder of coordination of movements, a shaky gait, accompanied by rotational movements and paralysis. Thiamine is reproduced by microflora and protozoa in the rumen of ruminants. It is well absorbed, but it is destroyed in the alkaline environment of the intestine, so it is used after feeding or parenterally for hypo- and avitaminosis B1, polyneuritis of various origins, atony of the muscles of the stomach and intestines, to accelerate the growth of animals and birds. Assign inside, subcutaneously and intramuscularly.
The need for vitamin B1 per 1 kilogram of feed in chickens is 1 milligram, in pigs 3 milligrams. With a therapeutic purpose, doses are given that are 3-8 times larger. Doses intramuscularly and subcutaneously (g): horses and cattle - 0.1-0.3, small cattle and pigs - 0.005-0.06, calves - 0.01-0.06, dogs - 0.001-0, 01, chickens and geese - 10-25 mg; chickens - 1-2 mg per head per day. Inside: chickens - 3-4 mg, piglets - 25-40 mg.
Squirrels - the main "workers" of the cell are natural biopolymers built from the remains of 20 amino acids. The composition of protein macromolecules can include from several tens to hundreds of thousands and even millions of amino acid residues, and the properties of the protein depend significantly on the order in which these residues are located one after another. Therefore, it is obvious that the number of possible proteins is practically unlimited.
Amino acids call organic compounds in which the carboxyl (acid) group COOH and the amino group NH 2. attached to the same carbon atom.
Fig.1 Structural formula of amino acids
The structure of such a molecule is described by a structural formula (Fig. 1), where R is a radical that is different for different amino acids. Thus, the composition of amino acids includes all four organogens C, O, H, N, and sulfur S can be included in some radicals.
According to the ability of a person to synthesize amino acids from their precursors, they are divided into two groups:
- Essential: Tryptophan, Phenylalanine, Lysine, Threonine, Methionine, Leucine, Isoleucine, Valine, Arginine, Histidine;
- Interchangeable: Tyrosine, Cysteine, Glycine, Alanine, Serine, Glutamic Acid, Glutamine, Aspartic Acid, Asparagine, Proline
Essential amino acids must be supplied to the human body with food, since they are not synthesized by humans, although some non-essential amino acids are not synthesized in the human body in sufficient quantities and must also be supplied with food.
Chemical formulas of 20 standard amino acids:
The structure of a protein molecule supported by covalent bonds between amino acid residues is called primary . In other words, the primary structure of a protein is determined by a simple sequence of amino acid residues. These residues can be placed in space in a quite definite way, forming a secondary structure. The most characteristic secondary structure is the α-helix, when amino acid chains seem to form a screw thread.
One of the most amazing properties macromolecules is that α-helices with left and right "thread" occur in wildlife with significantly different probabilities: there are almost no macromolecules "twisted" to the right. The asymmetry of biological substances with respect to mirror reflection was discovered in 1848 by the great French scientist L. Pasteur. Subsequently, it turned out that this asymmetry is inherent not only in macromolecules (proteins, nucleic acids), but also in organisms as a whole. How the predominant helicity of macromolecules arose and how it was further fixed in the course of biological evolution - these questions are still debatable and do not have an unambiguous answer.
The most complex and thin peculiarities structures that distinguish one protein from another are associated with the spatial organization of the protein, which is called tertiary structure. In fact, we are talking about the fact that helical chains of amino acid residues are folded into something resembling a ball of thread; As a result, rather long chains occupy a relatively small volume in space. The nature of clotting into a ball is by no means accidental. On the contrary, it is uniquely defined for each protein. It is thanks to the tertiary structure that the protein is able to perform its unique catalytic, enzymatic functions, when, as a result of the targeted capture of reagents, they are synthesized into complex chemical compounds comparable in complexity to the protein itself. None of the chemical reactions carried out by proteins can occur in the usual way.
In addition to the tertiary structure, the protein may have a quaternary structure; when there is a structural relationship between two or more proteins. In fact, we are talking about the union of several "coils" of polypeptide chains.
Nucleic acids(from lat. nucleus- core) - high-molecular organic phosphorus-containing compounds, biopolymers. The polymeric forms of nucleic acids are called polynucleotides. Chains of nucleotides are connected through a phosphoric acid residue (phosphodiester bond). Since there are only two types of heterocyclic molecules in nucleotides, ribose and deoxyribose, there are only two types of nucleic acids - deoxyribonucleic ( DNA) and ribonucleic ( RNA). Nucleic acids DNA and RNA are present in the cells of all living organisms and perform the most important functions of storing, transmitting and implementing hereditary information. One of the basic axioms of biology states that hereditary information about the structure and functions of a biological object is transmitted from generation to generation in a matrix way, and nucleic acids are carriers of this information.
These biopolymers are, at first glance, simpler than proteins. The "alpha-vit" of nucleic acids consists of only four "letters", which are nucleotides - pentose sugars, to which one of the five nitrogenous bases is attached: guanine (G), adenine (A), cytosine (C) , thymine (T) and uracil (U).
 |
|||
| adenine | Guanine | Timin | Cytosine |
Rice. 2 The structures of the bases most often found in DNA
In ribonucleic acid (RNA), sugar is the ribose carbohydrate (C 5 H 10 O 5), and in deoxyribonucleic acid (DNA) it is the deoxyribose carbohydrate (C 5 H 10 O 4), which differs from ribose only in that about one th of the carbon atoms, the OH group is replaced by a hydrogen atom. Three of these nitrogenous bases - G, A and C - are part of both RNA and DNA. The fourth nitrogenous base in these acids is different - T is included only in DNA, and Y is only in RNA. The units of nucleotides are linked by phosphodiester bonds of the phosphoric acid residue H 3 PO 4.
Relative molecular weights of nucleic acids reach values of 1500,000-2,000,000 or more. The secondary structure of DNA was established by X-ray diffraction analysis in 1953 by R. Franklin, M. Wilkins, J. Watson and F. Crick. It turned out that DNA forms helically twisted strands, and the nitrogenous base of one strand of DNA is connected by hydrogen bonds with a certain base of the other strand: adenine can only be associated with thymine, and cytosine can only be associated with guanine (Fig. .3). Such connections are called complementary(additional). It follows that the order of the bases in one strand uniquely determines the order in the other strand. It is with this that the most important property of DNA is connected - the ability to reproduce itself (replication). RNA does not have a double helical structure and is built like one of the strands of DNA. There are ribosomal (rRNA), messenger (mRNA) and transport (tRNA). They differ in the roles they play in cells.
Rice. 3 Different shapes of the DNA double helix
What do the nucleotide sequences in nucleic acids mean? Every three nucleotides (they are called triplets or codons) code for a particular amino acid in a protein. For example, the sequence of UCG gives a signal for the synthesis of the amino acid serine. The question immediately arises: how many different triplets can be obtained from four "letters"? It is easy to figure out that there can be 4 3 = 64 such triplets. But only 20 amino acid residues can participate in the formation of proteins, which means that some of them can be encoded by different triplets, which is observed in nature.
For example, leucine, serine, arginine are encoded by six triples, proline, valine and glycine by four, etc. This property of the triplet genetic code is called degeneracy or redundancy. It should also be noted that for all living organisms, protein coding occurs in the same way. (universality of coding). At the same time, the nucleotide sequences in DNA cannot be read in any other way than the only way. (non-overlapping codons).
Sulfur is an element of group VI of the periodic system with atomic number 16. Sulfur is relatively stable in the free state, under normal conditions it is in the form of an S8 molecule with a cyclic structure. Natural sulfur consists of a mixture of four stable isotopes with at. m. 32, 33, 34 and 36. When forming chemical bonds, sulfur can use all six electrons of the outer electron shell (sulfur oxidation states: 0, 2, 4 and 6).
Sulfur is either crystalline (in the form of a dense mass) or amorphous (fine powder). According to its chemical properties, sulfur is a typical metalloid and combines with many metals.
In nature, sulfur is found both in its native state and in the composition of sulfur and sulfate minerals (gypsum, sulfur pyrite, Glauber's salt, lead luster, etc.).
The Russian name of the element comes from the ancient Indian (Sanskrit) word "sira" - light yellow. The prefix "thio", often applied to sulfur compounds, comes from the Greek name for sulfur - "teion" (divine, heavenly), since sulfur has long been a symbol of combustibility; fire was considered the property of the gods, until Prometheus, as the myth says, brought it to people.
Sulfur has been known to mankind since ancient times. Found in nature in a free state, it attracted attention with its characteristic yellow color, as well as the pungent smell that accompanied its burning. It was also believed that the smell and the blue flame spread by burning sulfur warded off demons.
Sulfur dioxide, an asphyxiant gas formed during the combustion of sulfur, was used in ancient times to bleach fabrics. During the excavations of Pompeii, a picture was found, which depicts a baking sheet with sulfur and a device for hanging matter over it. Sulfur and its compounds have long been used for the preparation of cosmetics and for the treatment of skin diseases. And a very long time ago it began to be used for military purposes. So, in 670, the defenders of Constantinople burned the Arab fleet with the help of "Greek fire". it was a mixture of saltpeter, coal and sulfur. The same substances were part of the black powder used in Europe in the Middle Ages and until the end of the 19th century.
In hydrogen and oxygen compounds, sulfur is in the composition of various anions, forms many acids and salts. Most sulfur-containing salts are sparingly soluble in water.
Sulfur forms oxides with oxygen, the most important of which are sulfurous and sulfuric anhydrides. Being in the same group with oxygen, sulfur has similar redox properties. With hydrogen, sulfur forms a gas that is readily soluble in water - hydrogen sulfide. This gas is highly toxic due to its ability to bind strongly to copper cations in respiratory chain enzymes.
Sulfuric acid, one of the most important sulfur compounds, was apparently discovered by the 10th century, since the 18th century, it has been produced on an industrial scale and soon it becomes the most important chemical product, necessary in both metallurgy and the textile industry, and in other, very different industries. In this regard, an even more intensive search for sulfur deposits began, the study of the chemical properties of sulfur and its compounds and the improvement of methods for their extraction from natural raw materials.
