Cis ser gly lys arg. Siberian State Medical University. Thyroid hormones

Peptides- natural or synthetic compounds, the molecules of which are built from α-amino acid residues connected by peptide (amide) bonds. Peptides may also contain a non-amino acid component. Based on the number of amino acid residues included in peptide molecules, dipeptides, tripeptides, tetrapeptides, etc. are distinguished. Peptides containing up to ten amino acid residues are called oligopeptides containing more than ten amino acid residues – polypeptides. Natural polypeptides with a molecular weight greater than 6000 are called proteins.

The amino acid residue of peptides that carries a free α-amino group is called N-terminal, and the residue that carries a free α-carboxyl group is called C-terminal. The name of the peptide is formed from the names of the amino acid residues included in its composition, listed sequentially, starting with the N-terminal one. In this case, trivial names of amino acids are used, in which the suffix “in” is replaced by “silt”. The exception is the C-terminal residue, the name of which coincides with the name of the corresponding amino acid. All amino acid residues included in the peptides are numbered starting from the N-terminus. To record the primary structure of a peptide (amino acid sequence), three- and one-letter designations for amino acid residues are widely used (for example, Ala-Ser-Asp-Phe-GIy is alanyl-seryl-asparagyl-phenylalanyl-glycine).

Individual representatives of peptides

Glutathione- tripeptide -glutamylcysteinylglycine, found in all animal and plant cells and bacteria.

Glutathione is involved in a number of redox processes. It functions as an antioxidant. This is due to the presence of cysteine ​​in its composition and determines the possibility of the existence of glutathione in reduced and oxidized forms.

KarnozAndn(from Latin carnosus - meat, caro - meat), C 9 H 14 O 3 N 4, is a dipeptide (β-alanylhistidine), consisting of the amino acids β-alanine and L-histidine. Discovered in 1900 by V.S. Gulevich in meat extract. Molecular weight 226, crystallizes in the form of colorless needles, highly soluble in water, insoluble in alcohol. Found in the skeletal muscles of most vertebrates. Among fish there are species in which carnosine and its constituent amino acids are absent (or only L-histidine or β-alanine only). There is no carnosine in the muscles of invertebrates. The carnosine content in vertebrate muscles usually ranges from 200 to 400 mg% of their wet weight and depends on their structure and function; in humans - about 100-150 mg%.

Carnosine (β-alanyl-L-histidine) Anserine (β-alanyl-1-methyl-L-histidine)

The influence of carnosine on the biochemical processes occurring in skeletal muscles is varied, but the biological role of carnosine has not been definitively established. The addition of carnosine to a solution bathing the muscle of an isolated neuromuscular drug causes contraction of the fatigued muscle to resume.

Dipeptide anserine(N-methylcarnosine or β-alanyl-1-methyl-L-histidine), similar in structure to carnosine, is absent in human muscles, but is present in the skeletal muscles of those species whose muscles are capable of rapid contractions (rabbit limb muscles, pectoral muscle birds). The physiological functions of β-alanyl-imidazole dipeptides are not entirely clear. Perhaps they perform buffering functions and maintain pH in skeletal muscle contracting under anaerobic conditions. However, it is clear that carnosine And anserine stimulate the ATPase activity of myosin in vitro, increase the amplitude of muscle contraction, previously reduced by fatigue. Academician S.E. Severin showed that imidazole-containing dipeptides do not directly affect the contractile apparatus, but increase the efficiency of the ion pumps of the muscle cell. Both dipeptides form chelate complexes with copper and promote the absorption of this metal.

Antibiotic gramicidin S isolated from Bacillus brevis and is a cyclic decapeptide:

Gramicidin S

In structure gramicidinS there are 2 ornithine residues, derivatives of the amino acid arginine, and 2 residues of D-isomers of phenylalanine.

OxytotzAndn- a hormone produced by the neurosecretory cells of the anterior nuclei of the hypothalamus and then transported along nerve fibers to the posterior lobe of the pituitary gland, where it accumulates and from where it is released into the blood. Oxytocin causes contraction of the smooth muscles of the uterus and, to a lesser extent, the muscles of the bladder and intestines, and stimulates the secretion of milk by the mammary glands. By its chemical nature, oxytocin is an octapeptide, in a molecule of which 4 amino acid residues are linked into a ring by cystine, also connected to a tripeptide: Pro-Leu-Gly.

oxytocin

Let's consider neuropeptides (opiate peptides). The first two neuropeptides, called enkephalins, were isolated from animal brains:

Tyr - Gli - Gli - Fen - Met- Met-enkephalin

Tyr - Gli - Gli - Fen - Lei-Leu-enkephalin

These peptides have an analgesic effect and are used as medicines.

13.. Due to what bonds can a copolymer be formed from the two peptides below?

A) ala-met-arg-cis-ala-gli-ser-gli-cis-tre;

b) lys-glu-arg-cis-arg-gly-tre-ser-lys-tre-glu-ser.

14. How, using the biuret method for determining protein and ammonium sulfate, to establish the ratio between albumins and globulins in blood serum?

15. The ratio of the amount of albumin to the amount of globulin in the patient’s blood serum is 1.5. Calculate the globulin content if the albumin concentration is 5.0 g%.

16. Name the two main configurations of a protein molecule and indicate the differences between them.

17. At what level of spatial organization are globular and fibrillar proteins distinguished?

18. Name the most important groups of basic proteins.

19. Why do protamines and histones differ in their basic character?

20. Why do protamines and histones coagulate under high heat only in a highly alkaline environment?

LESSON 3 “Chemistry of complex proteins. Determination of components of phospho- and nucleoproteins"

Purpose of the lesson : become familiar with the classification and structure of complex proteins, especially nucleoproteins, which play a leading role in the storage and transmission of genetic information (DNA and RNA), as well as the most important chromoproteins (hemoglobin).

The student should know:

1. Classes of complex proteins, the principle of their division into classes, the principle of nomenclature

2. The chemical nature of prosthetic groups of complex proteins.

3. Components of the prosthetic group of nucleoproteins and chromoproteins (in particular, hemoglobin).

4. Spatial organization of nucleic acids.

5. Differences in the composition and structure of RNA and DNA

6.Functions of DNA and RNA, types of RNA, their localization.

7. Prosthetic group of hemoglobin, its components, the role of iron in the composition of heme.

8. Factors whose impact can cause changes in DNA structure with informational consequences.

The student must be able to:

1. Construct (schematically) a complementary chain to a section of a given fragment of one of the DNA chains.

2. Determine, based on the results of a qualitative analysis of nucleic acid hydrolyzate, whether DNA or RNA was hydrolyzed

3. Distinguish between the types of hemoglobin and use the designations adopted for them (oxyhemoglobin, reduced hemoglobin, carboxyhemoglobin, etc.

4. Find errors in segments of supposedly complementary DNA strands presented for evaluation

The student must get an idea: about the predominant localization of complex proteins in the human body, their biological significance, about the threats that mutagenic effects pose to the existence of species.

Classroom work

Laboratory work (Determination of phospho-

And nucleoproteins)

1. Isolation of casein from milk. Casein (one of the phosphoproteins) is contained in milk in the form of a soluble calcium salt, which decomposes when acidified, and casein precipitates. Excess acid interferes with precipitation, since at pH values ​​below 4.7 (the isoelectric point of casein), the protein molecules are recharged and casein goes back into solution.

Progress. To 2 ml of milk add an equal volume of distilled water and 2 drops of 10% acetic acid. Collect the casein that falls out in the form of flakes on a filter and rinse with water.

Hydrolysis of nucleoproteins

Progress. Place 1 g of yeast in a round-bottomed flask, add 20 ml of a 10% sulfuric acid solution and the same amount of distilled water. Close the flask with a reflux stopper and boil under pressure for 1.5 hours at low heat. Cool the liquid, add distilled water to the original volume, and filter. Use the filtrate for the following qualitative reactions:

a) biuret reaction(for detection of polypeptides). To 5 drops of the resulting hydrolyzate add 10 drops of a 10% solution of sodium hydroxide and 1 drop of a 1% solution of copper sulfate. The liquid turns pink;

b) silver test(to detect purine bases). Add 5 drops of a 2% ammonia solution of silver nitrate to 5 drops of hydrolyzate. After 3-5 minutes, a small brown precipitate of silver compounds of purine bases precipitates;

c) qualitative Molisch reaction(to detect the pentose group). To 10 drops of hydrolyzate, add 2 - 3 drops of a 1% solution of thymol in ethanol, mix and lower an equal volume of concentrated sulfuric acid along the wall - a distinct red ring;

d) molybdenum sample(for phosphoric acid detection). Add 5 drops of molybdenum reagent to 5 drops of hydrolyzate and boil for several minutes. A lemon-yellow color appears, and upon cooling, a yellow crystalline precipitate of a complex compound of ammonium phosphomolybdate appears.

Give reasoned answers to the tasks suggested below:

1. What structural components make up DNA? In what order are they connected to each other?

2. Construct a complementary chain to the site. the DNA fragment shown below (- A - G - G - C - T- G-T) so that the resulting chain is an RNA fragment:

3. Construct a complementary chain to a section of one of the DNA chains presented below:

-A - G - G - C - T -

: - : - : - : - :

-? - ? - ? - ? - ? -

4.Find errors in the DNA fragment below:

-T - U - A - U - C - T - T - G-

: -: - : - : : : : :

A - A - T - A - G - A - A - U-

5. The oligonucleotide was hydrolyzed in two ways. In the first case, mononucleotides were determined in the hydrolyzate A, G, C and T(the latter is found in the hydrolyzate in an amount 2 times higher than the others), as well as dinucleotides G - A, A - T And T - T. In the second case, along with free nucleotides, a dinucleotide was found G - C.

Determine the nucleotide sequence in the original product?

6. The test solution exhibits a positive biuret reaction and forms a precipitate upon boiling and the addition of concentrated mineral acids, as well as sulfosalicylic acid.

Draw up a research plan, the purpose of which is to find out whether a simple or complex protein is in solution. If a complex protein is detected, how to establish (or exclude) that it is hemoglobin.

7. Explain the basis for dividing complex proteins into classes.

8. Give a brief description of all classes of complex proteins.

9. Remember the structural formulas of prosthetic groups of nucleic acids.

10. Characterize the nitrogenous bases that make up nucleic acids and list the differences between DNA and RNA (by localization, structure, functions).

11. Name the minimum information element in the structure of DNA and RNA.

12. Understand how the role of DNA and RNA is realized as sources of information.

13. Name two subgroups of chromoproteins and the differences between them.

14. To consolidate an understanding of the structure of hemoglobin (to study the components of the protein part and the components of the heme, as well as their role in the main function of hemoglobin).

LESSON 4 (final)

When preparing for the final lesson, check whether you have mastered the section "Structure and functions of proteins" using the following questions (use lecture materials and textbooks when preparing):

1. Formulate the concept of “Life”, including in the definition all the elements that are the subject of biochemistry.

2. Define the subject of biochemistry and list the issues that this science deals with.

3. Name the most important supramolecular formations of living things and the groups of molecules that make them up

4. Define the class “Proteins”

5. Define the class “Amino acids”.

6. Write the structural formulas of all tripeptides that can be built from histidine, alanine and valine.

7. Which of the following peptides are acidic, basic, or neutral and indicate the net electrical charge of each. pro-ser-ser; ala-pro-leu-thr; met-gly-ala; glu-his-ser; cys-lys-arg, glu-arg-lys; his-glu.

8. List the approaches to protein classification known to you

9. Name groups of proteins that differ in composition.

10. Name groups of proteins that differ in three-dimensional structure.

11. Name groups of complex proteins.

12. Continue the phrase “Loss of the native conformation under the influence of chemical, physical and other factors without violating the amino acid sequence is........”

13. List the types of chemical bonds that are broken during denaturation.

14. List in logical order the steps required to isolate proteins from tissues.

15. Draw the structural formulas of the nitrogenous bases that make up mononucleotides.

16. Draw the structural formulas of AMP, HMP, CMP, TMP and UMP.

17. Describe the method of connection between mononucleotides in a polynucleotide.

18. Name the differences between DNA and RNA in composition, structure, localization and function.

19. What type of protein is hemoglobin?

20. Name the structural features of globin.

21. Draw the structural formula of heme, name the connections between heme and globin.

22. What causes the diversity of functions of proteins?

23. List the biological functions of proteins.

Topic: “The nature and properties of enzymes” (lessons 5-9)

Target: study the chemical nature, functions and properties of biological catalysts - enzymes.

The meaning of the topic. Metabolism, an obligatory and most important feature of living organisms, is made up of many different chemical reactions, which involve compounds entering the body from the outside and compounds of endogenous origin. In the process of studying this section of the discipline, one learns that all chemical reactions in living things occur with the participation of catalysts, that catalysts in living things (enzymes or enzymes) are substances of a protein nature, that the properties of enzymes and their behavior depend on the characteristics of the environment.

When studying this section, information is also acquired about how the activity of enzymes is regulated in the whole organism, and general ideas are created about the connection of a number of pathological processes with changes in the activity or quantity of enzymes, information about the principles of quantitative characteristics of enzymes, and their use for diagnostic and therapeutic purposes.

Squirrels- high molecular weight natural polymers consisting of amino acid residues , connected by a peptide bond; are the main component of living organisms and the molecular basis of life processes.

More than 300 different amino acids are known in nature, but only 20 of them are part of the proteins of humans, animals and other higher organisms. Each amino acid has carboxyl group, amino group in the α-position (at the 2nd carbon atom) and radical (side chain), which differs among different amino acids. At physiological pH (~7.4), the carboxyl group of amino acids usually dissociates and the amino group is protonated.

All amino acids (with the exception of glycine) contain an asymmetric carbon atom (i.e., such an atom, all four valence bonds of which are occupied by different substituents, it is called a chiral center), therefore they can exist in the form of L- and D-stereoisomers (the standard is glyceraldehyde ):

For the synthesis of human proteins, only L-amino acids are used. In proteins with a long lifespan, L-isomers can slowly acquire the D-configuration, and this happens at a certain rate characteristic of each amino acid. Thus, dentin proteins of teeth contain L-aspartate, which transforms into the D-form at human body temperature at a rate of 0.01% per year. Since dental dentin is practically not exchanged or synthesized in adults in the absence of trauma, the D-aspartate content can be used to determine a person’s age, which is used in clinical and forensic practice.

All 20 amino acids in the human body differ in structure, size and physicochemical properties of the radicals attached to the α-carbon atom.

The structural formulas of 20 proteinogenic amino acids are usually given in the form of the so-called proteinogenic amino acid tables:

Recently, single-letter designations have been used to designate amino acids; a mnemonic rule (fourth column) is used to remember them.

2. The process of converting an amino acid into a keto acid in the presence of the enzyme oxidase is called

1) transamination

3) oxidative deamination

4) hydroxylation

5) non-oxidative deamination

3. In the series of amino acids, alanine is

1)
2)
3)
4)
5)

4. The tripeptide glycis-cis-phene corresponds to the formula

5. An aromatic amino acid is

1) threonine

3) tryptophan

5) tyrosine

6. The peptide bond is

7. Natural amino acids are highly soluble in water, because contain

1) benzene ring

2) heterocyclic rings

3) amino group and carboxyl group

4) thio group

5) hydroxyl group

8. The tripeptide ala-tre-val corresponds to the formula

9. The second amino group in the radical contains an acid

1) aspartic

3) tryptophan

5) methionine

10. A heterocyclic amino acid is

1) threonine

2) phenylalanine

3) glutamine

4) histidine

5) cysteine

11. The specific reaction of α-amino acids is

1) formation of salts

2) elimination of ammonia

3) interaction with DNFB

4) lactam formation

5) formation of diketopiperazine

12. The tripeptide fEN-lys-glu corresponds to the formula

13. A dibasic amino acid is

3) methionine

4) tryptophan

5) glutamine

14. The reaction of interconversion in the body of the amino group and the carbonyl group of acids under the action of the enzyme trans-aminase is the reaction

1) hydroxylation

2) reductive amination

3) transamination

5) oxidative deamination

15. In amino acids, the amino group is protected by the reaction of the amino acid with

1)	PCL 5
2)
3)	CH3Cl
4)	C2H5OH
5)	HCl

16. The tripeptide ser-cis-phen corresponds to the formula

17. In amino acid solutions, the reaction of the medium

3) neutral

3) slightly alkaline

4) slightly acidic

5) depends on the number of amino and carboxyl groups

18. An aliphatic amino acid is

1) histidine

3) tryptophan

5) phenylalanine

19. Among the following amino acids, histidine is

20. general formula of dipeptides

21. The process of converting an amino acid into an unsaturated acid, occurring in the presence of enzymes, is called

1) transamination

3) hydroxylation

4) oxidative deamination

5) non-oxidative deamination

22. The amino acid tyrosine corresponds to the formula

23. Only hydroxyl-containing amino acids are presented in the series

1) val-cis-lys

2) tyr-tre-ser

3) gis-met-lys

4) ala-val-fal

5) ser-liz-three

24. The tripeptide asp-met-lys corresponds to the formula

25. Amino alcohol is formed as a result of decarboxylation

26. Diketopiperazine corresponds to the formula

27. Only aliphatic amino acids that do not contain additional functional groups in the radical are contained in the series

1) gis-ala-fal

2) val-ley-iley

3) val-tre-asp

4) gly-glu-tyr

5) cis-met-tre

28. The tripeptide his-leu-phen corresponds to the formula

29. Cadaverine or 1,5-diaminpentane (cadaveric poison) is formed as a result of a decarboxylation reaction

1) isoleucine

2) leucine

4) methionine

5) histidine

30. When valine is acylated with acetyl chloride, it forms

31. Amino acids don't react With

32. The tripeptide met-lys-leu corresponds to the formula

33. In vitro deamination reaction is the interaction of an amino acid with

1) ethanol

2) hydrochloric acid

3) nitric acid

4) nitrous acid

34. Diketopiperazine is formed by the interaction

1) amino acids with pcl 5

2) two amino acids when heated

3) amino acids with NaOH

4) amino acids with HCl

5) amino acids when heated with Ba(OH) 2

35. The amino acid lysine corresponds to the formula

36. Composition of amino acids not included

4) carbon

5) oxygen

37. The tripeptide asn-tre-ser corresponds to the formula

38. Putrescine or 1,4-diaminobutane (cadaveric poison) is formed during decarboxylation

39. Amino alcohol is formed as a result of decarboxylation

1) histidine

2) tyrosine

3) threonine

5) leucine

40. With complete hydrolysis of peptides in an acidic environment, a mixture is formed

1) amino acids

2) esters and amino acids

3) salts of primary amines

4) amines and amino acids

5) diketopiperazines

41. The tripeptide ala-gli-glu corresponds to the formula

42. Activation of the carboxyl group of an amino acid with a protected amino group is carried out by interaction with

43. The number of moles of KOH required to completely neutralize aspartic acid is

5) there is no reaction with KOH

44. The tripeptide fen-TPE-glu corresponds to the formula

45. Hydrogen fluoride is released when an amino acid interacts with

46. ​​The bipolar ion of valine corresponds to the formula

47. The transamination reaction occurs in the body with the participation of an enzyme

2) oxidases

3) transaminases

5) acetyl coenzyme A

48. The tripeptide met-glu-ala corresponds to the formula

49. A heterocyclic amino acid is

3) tyrosine

4) phenylalanine

5) isoleucine

50. When leucine is acetylated with acetyl chloride, it forms

1) cis, glu

2) gli, meth

3) glu, shaft

4) cis, met

5) three, three

52. The tripeptide fen-gis-lei corresponds to the formula

53. Putrescine (1,4-diaminobutane) or cadaveric poison, formed by decarboxylation

2) threonine

3) histidine

4) isoleucine

5) ornithine

54. An amino acid with an activated carboxyl group is

55. Diketopiperazine serine is represented by the formula

56. The tripeptide ala-fen-tir corresponds to the formula

57. When determining the number of amino groups in amino acids using the Van Slyke method, use

58. The bipolar lysine ion is represented by the formula

59. The amphoteric nature of amino acids is explained by the presence in their molecules

1) carboxyl group

2) amino groups

3) carboxyl and amino groups

4) carboxyl and thiol groups

5) amino group of the benzene ring

60. Tripeptide val-met-asp corresponds to