CH 3 CH 3
IET is in the region of pH≈7
GLI - GLU
(CH 2) 2 -COOH (CH 2) 2 - COOH
IET is in the pH region<7
GLI - LIZ
H 2 N–CH 2 –CO–NH–CH–COOH ↔ H 3 N + –CH 2 –CO–NH–CH–COO ‾
(CH 2) 4 –NH 2 (CH 2) 4 – NH 2
IET is in the pH>7 region
16.4 PROTEINS
Proteins are high-molecular nitrogen-containing biological macromolecules consisting of biogenic α,L-amino acids linked in a linear sequence by peptide (amide) bonds.
The simplest protein is a polypeptide containing at least 70 amino acid residues in its structure.
Proteins are the most important components of the cell, accounting for at least 50% of dry weight. They carry out the implementation of genetic information, the construction of cell and body structures, the occurrence of metabolic processes, and the body’s immune defense.
The difference between peptides and proteins is not only quantitative, but also qualitative. After the biosynthesis of the polypeptide chain of proteins on ribosomes and its subsequent convergence into the hydrophilic environment of the cytosol, higher levels of its organization spontaneously form - secondary, tertiary, and for a number of proteins - quaternary structure.
1. Primary structure– is defined as a linear sequence of biogenic amino acids linked by peptide bonds. It is genetically determined for each specific protein in the nucleotide sequence of messenger RNA. The primary structure also determines higher levels of organization of protein molecules. Knowing the primary structure, it is possible to consistently obtain a protein synthetically (insulin was synthesized for the first time, and subsequently many other proteins, so synthetic polypeptides became widespread for the treatment of AIDS and many other diseases).
2. Secondary structure protein - a local conformation of a polypeptide chain, resulting from the rotation of its individual sections, leading to twisting, folding or bending of this section of the chain. The secondary structure can be represented by an α-helix, β-structure (structure
folded sheet).
3. Tertiary structure- conformation (location in space) of the entire polypeptide chain, determined by the interaction of elements of the secondary structure of both nearby and distant amino acid residues. All types of interactions take part in its formation and stabilization: hydrophobic, van der Wals, electrostatic (ionic), disulfide covalent bonds. The most significant are hydrophobic interactions and disulfide bonds.
4. Quaternary structure squirrel. A method of spatial arrangement of individual polypeptide chains (identical or different) with a tertiary structure, leading to the formation of a structurally and functionally unified macromolecular formation ( multimer).
Each individual polypeptide chain in the multimer structure is called protomer. The protomers are sterically complementary and bind the structure together through noncovalent bonds. For example, the protein molecule that makes up the blood, hemoglobin, consists of several symmetrically constructed particles (identical polypeptide chains) that have the same primary, secondary and tertiary structure.
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.
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.
summary of other presentations“Metabolism and cell energy” - Definition. Plastic exchange. Digestive organs. Preparing students for open-ended tasks. Chemical transformations. Questions with “yes” or “no” answers. Metabolism. Metabolism. Text with errors. A task with a detailed answer. Test tasks. Energy exchange.
"Metabolism" - Properties of the genetic code. Molecular weight of one amino acid. Genetic code. The initial part of the molecule. Plastic exchange. Transcription. Protein. DNA. Determine the length of the corresponding gene. Reactions of assimilation and dissimilation. A section of the right strand of DNA. Define the terms. Autotrophs. Protein biosynthesis. What primary structure will the protein have? A protein consisting of 500 monomers. Broadcast.
“Energy metabolism” 9th grade - Glucose is the central molecule of cellular respiration. ATP in numbers. The concept of energy metabolism. Autotrophs. PVA – pyruvic acid C3H4O3. Structure of ATP. ATP is a universal source of energy in the cell. Conversion of ATP to ADP. Fermentation is anaerobic respiration. Metabolism. Energy metabolism in the cell. Fermentation. Energy metabolism (dissimilation). Mitochondria. The aerobic stage is oxygen. Summary equation of the aerobic phase.
“Stages of Energy Metabolism” - Summary Equation. Types of nutrition of organisms. The splitting process. Metabolism. Oxidation of PVC. Electron transport chain. Energy release. Krebs cycle. Describe the reactions. Oxidative decarboxylation. Catabolism. Aerobic respiration. Stages of aerobic respiration. Preparatory stage. Oxygen splitting. Solar energy. Where does ATP synthesis take place? Oxygen-free stage. Fill in the blanks in the text.
“Carbohydrate metabolism” - Summary of the Krebs cycle. Triosephosphate isomerase. Sucrose. Chemiosmotic model of ATP synthesis. Factors influencing enzyme activity. Metabolism. Glycolysis. Aldolaza. Classification of enzymes. Stocking. Stages of glucose oxidation. Formation of branches. Enzymes. Protein components of the mitochondrial ETC. Enzymes. The main stages of carbohydrate metabolism. Enolase. Glycogen synthesis. Oxidation of acetyl-CoA to CO2.
“Energy metabolism” - The process of energy metabolism. Glycolysis. Energy released in glycolysis reactions. Enzymes of the oxygen-free stage of energy exchange. The fate of the PVK. Lactic acid fermentation. Lactic acid. Biological oxidation and combustion. Oxidation of substance A. Preparatory stage. Repetition. Combustion. Energy exchange.
Data on the mechanism of action of ACTH on the synthesis of steroid hormones indicate a significant role of the adenylate cyclase system. It is believed that ACTH interacts with specific receptors on the outer surface of the cell membrane (the receptors are represented by proteins in complex with other molecules, in particular sialic acid). The signal is then transmitted to the enzyme adenylate cyclase, located on the inner surface of the cell membrane, which catalyzes the breakdown of ATP and the formation of cAMP. The latter activates protein kinase, which in turn, with the participation of ATP, phosphorylates cholinesterase, which converts cholesterol esters into free cholesterol, which enters the adrenal mitochondria, which contains all the enzymes that catalyze the conversion of cholesterol into corticosteroids. Somatotropic hormone (GH, growth hormone, somatotropin) is synthesized in the acidophilic cells of the anterior pituitary gland; its concentration in the pituitary gland is 5–15 mg per 1 g of tissue. Human GH consists of 191 amino acids and contains two disulfide bonds; N- and C-terminal amino acids are represented by phenylalanine. STH has a wide range of biological effects. It affects all cells of the body, determining the intensity of metabolism of carbohydrates, proteins, lipids and minerals. It enhances the biosynthesis of protein, DNA, RNA and glycogen and at the same time promotes the mobilization of fats from storage and the breakdown of higher fatty acids and glucose in tissues. In addition to activating assimilation processes, accompanied by an increase in body size and skeletal growth, growth hormone coordinates and regulates the rate of metabolic processes. Many of the biological effects of this hormone are carried out through a special protein factor formed in the liver under the influence of the hormone - somatomedin. By its nature it turned out to be a peptide with a mol. weighing 8000. Thyroid-stimulating hormone (TSH, thyrotropin) is a complex glycoprotein and, in addition, contains two α- and β-subunits, which individually do not have biological activity: they say. its mass is about 30,000. Thyrotropin controls the development and function of the thyroid gland and regulates the biosynthesis and secretion of thyroid hormones into the blood. The primary structure of the α- and β-subunits of thyrotropin has been completely deciphered: α-subunit containing 96 amino acid residues; β-subunit of human thyrotropin, containing 112 amino acid residues, To gonadotropic hormones (gonadotropins) include follicle-stimulating hormone (FSH, follitropin) and luteinizing hormone (LH, lutropin). Both hormones are synthesized in the anterior lobe of the pituitary gland and are complex proteins - glycoproteins with a mol. weighing 25,000. They regulate steroid and gametogenesis in the gonads. Follitropin causes maturation of follicles in the ovaries in females and spermatogenesis in males. Lutropin stimulates the secretion of estrogen and progesterone in females, as well as the rupture of follicles with the formation of the corpus luteum, and in males it stimulates the secretion of testosterone and the development of interstitial tissue. The biosynthesis of gonadotropins, as noted, is regulated by the hypothalamic hormone gonadoliberin. Lutropin consists of two α- and β-subunits: the α-subunit of the hormone contains 89 amino acid residues from the N-terminus and differs in the nature of 22 amino acids.
29. Hormones of the posterior lobe of the pituitary gland: vasopressin, oxytocin. Chemical nature. The mechanism of their action, biological effect. Disorders of body functions associated with a lack of production of these hormones.
Hormones vasopressin and oxytocin synthesized by the ribosomal pathway. Both hormones are nonapeptides with the following structure: Vasopressin differs from oxytocin in two amino acids: it contains phenylalanine at position 3 from the N-terminus instead of isoleucine, and at position 8 it contains arginine instead of leucine. The main biological effect of oxytocin in mammals is associated with stimulation of contraction of the smooth muscles of the uterus during childbirth and muscle fibers around the alveoli of the mammary glands, which causes milk secretion. Vasopressin stimulates the contraction of smooth muscle fibers of blood vessels, exerting a strong vasopressor effect, but its main role in the body is to regulate water metabolism, hence its second name, antidiuretic hormone. In small concentrations (0.2 ng per 1 kg of body weight), vasopressin has a powerful antidiuretic effect - it stimulates the reverse flow of water through the membranes of the renal tubules. Normally, it controls the osmotic pressure of blood plasma and the water balance of the human body. With pathology, in particular atrophy of the posterior lobe of the pituitary gland, diabetes insipidus develops, a disease characterized by the release of extremely large amounts of fluid in the urine. In this case, the reverse process of water absorption in the kidney tubules is disrupted.
Oxytocin
Vasopressin
30. Thyroid hormones: triiodothyronine and thyroxine. Chemical nature, biosynthesis. The mechanism of action of hormones at the molecular level, biological effect. Changes in metabolism in hyperthyroidism. The mechanism of occurrence of endemic goiter and its prevention.
Thyroxine and triiodothyronine– the main hormones of the follicular part of the thyroid gland. In addition to these hormones (the biosynthesis and functions of which will be discussed below), a peptide hormone is synthesized in special cells - the so-called parafollicular cells, or C-cells of the thyroid gland, which ensure a constant concentration of calcium in the blood. It was named ≪ calcitonin≫. The biological effect of calcitonin is directly opposite to the effect of parathyroid hormone: it causes suppression of resorptive processes in bone tissue and, accordingly, hypocalcemia and hypophosphatemia. The thyroid hormone thyroxine, which contains iodine in 4 positions of the ring structure, is easily synthesized from L-thyronine. The biological effect of thyroid hormones extends to many physiological functions of the body. In particular, hormones regulate the rate of basal metabolism, growth and differentiation of tissues, metabolism of proteins, carbohydrates and lipids, water-electrolyte metabolism, activity of the central nervous system, digestive tract, hematopoiesis, function of the cardiovascular system, the need for vitamins, the body's resistance to infections, etc. Hypothyroidism glands in early childhood leads to the development of a disease known in the literature as cretinism. In addition to growth arrest, specific changes in the skin, hair, muscles, and a sharp decrease in the speed of metabolic processes, profound mental disorders are noted with cretinism; Specific hormonal treatment in this case does not give positive results. Increased function of the thyroid gland (hyperfunction) causes the development hyperthyroidism
L-thyroxine L-3,5,3"-triiodothyronine
31. Hormones of the adrenal cortex: glucocorticoids, mineralocorticoids. Chemical nature. Mechanism of action at the molecular level. Their role in the regulation of carbohydrate, mineral, lipid and protein metabolism.
Depending on the nature of the biological effect, hormones of the adrenal cortex are conventionally divided into glucocorticoids (corticosteroids that affect the metabolism of carbohydrates, proteins, fats and nucleic acids) and mineralocorticoids (corticosteroids that have a primary effect on the metabolism of salts and water). The first include corticosterone, cortisone, hydrocortisone (cortisol), 11-deoxycortisol and 11-dehydrocorticosterone, the second - deoxycorticosterone and aldosterone. Their structure, as well as the structure of cholesterol, ergosterol, bile acids, D vitamins, sex hormones and a number of other substances, is based on the condensed ring system of. Glucocorticoids have a diverse effect on metabolism in different tissues. In muscle, lymphatic, connective and adipose tissues, glucocorticoids, exhibiting a catabolic effect, cause a decrease in the permeability of cell membranes and, accordingly, inhibition of the absorption of glucose and amino acids; at the same time, in the liver they have the opposite effect. The end result of glucocorticoid exposure is the development of hyperglycemia, mainly due to gluconeogenesis. Mineralocorticoids(deoxycorticosterone and aldosterone) mainly regulate the metabolism of sodium, potassium, chlorine and water; they contribute to the retention of sodium and chloride ions in the body and the excretion of potassium ions in the urine. Apparently, sodium and chloride ions are reabsorbed in the kidney tubules in exchange for the excretion of other metabolic products,
cortisol
32. Parathyroid hormone and calcitonin. Chemical nature. Mechanism of action at the molecular level. Effect on calcium metabolism, hypercalcemia and hypocalcemia.
Protein hormones also include parathyroid hormone (parathyroid hormone). They are synthesized by the parathyroid glands. The bovine parathyroid hormone molecule contains 84 amino acid residues and consists of one polypeptide chain. It has been found that parathyroid hormone is involved in the regulation of the concentration of calcium cations and associated phosphoric acid anions in the blood. Ionized calcium is considered the biologically active form; its concentration ranges from 1.1–1.3 mmol/l. Calcium ions turned out to be essential factors that are not replaceable by other cations for a number of vital physiological processes: muscle contraction, neuromuscular excitation, blood clotting, cell membrane permeability, activity of a number of enzymes, etc. Therefore, any changes in these processes caused by a prolonged lack of calcium in food or a violation of its absorption in the intestine lead to increased synthesis of parathyroid hormone, which promotes the leaching of calcium salts (in the form of citrates and phosphates) from bone tissue and, accordingly, to the destruction of mineral and organic components of bones. Another target organ of parathyroid hormone is the kidney. Parathyroid hormone reduces the reabsorption of phosphate in the distal tubules of the kidney and increases the tubular reabsorption of calcium. In special cells - the so-called parafollicular cells, or C-cells of the thyroid gland, a hormone of peptide nature is synthesized, ensuring a constant concentration of calcium in the blood - calcitonin. Formula:
Calcitonin contains a disulfide bridge (between the 1st and 7th amino acid residues) and is characterized by an N-terminal cysteine and a C-terminal prolinamide. The biological effect of calcitonin is directly opposite to the effect of parathyroid hormone: it causes suppression of resorptive processes in bone tissue and, accordingly, hypocalcemia and hypophosphatemia. Thus, the constancy of the level of calcium in the blood of humans and animals is ensured mainly by parathyroid hormone, calcitriol and calcitonin, i.e. hormones of both the thyroid and parathyroid glands, and a hormone derived from vitamin D3. This should be taken into account during surgical therapeutic manipulations on these glands.
33. Hormones of the adrenal medulla - catecholamines: adrenaline and norepinephrine. Chemical nature and biosynthesis. The mechanism of action of hormones at the molecular level, their role in regulating the metabolism of carbohydrates, fats and amino acids. Metabolic disorders in diseases of the adrenal glands.
These hormones are structurally reminiscent of the amino acid tyrosine, from which they differ in the presence of additional OH groups in the ring and at the β-carbon atom of the side chain and the absence of a carboxyl group.
Adrenaline Norepinephrine Isopropyladrenaline
The human adrenal medulla weighing 10 g contains about 5 mg of adrenaline and 0.5 mg of norepinephrine. Their content in the blood is 1.9 and 5.2 nmol/l, respectively. In the blood plasma, both hormones are present both in a free state and in a state bound, in particular, to albumin. Small amounts of both hormones are deposited as a salt with ATP in nerve endings, released in response to stimulation. Moreover, they are all about They have a powerful vasoconstrictor effect, causing an increase in blood pressure, and in this respect their action is similar to the action of the sympathetic nervous system. The powerful regulatory effect of these hormones on carbohydrate metabolism in the body is known. Thus, in particular, adrenaline causes a sharp increase in blood glucose levels, which is due to the acceleration of glycogen breakdown in the liver under the action of the enzyme phosphorylase. The hyperglycemic effect of norepinephrine is much lower - approximately 5% of the effect of adrenaline. In parallel, there is an accumulation of hexose phosphates in tissues, in particular in muscles, a decrease in the concentration of inorganic phosphate and an increase in the level of unsaturated fatty acids in the blood plasma. There is evidence of inhibition of glucose oxidation in tissues under the influence of adrenaline. Some authors associate this action with a decrease in the rate of penetration (transport) of glucose into the cell. It is known that both adrenaline and norepinephrine are quickly destroyed in the body; Inactive products of their metabolism are excreted in the urine, mainly in the form of 3-methoxy-4-hydroxymandelic acid, oxoadrenochrome, methoxynoadrenaline and methoxyadrenaline. These metabolites are found in urine mainly in the form associated with glucuronic acid. Enzymes that catalyze these transformations of catecholamines have been isolated from many tissues and are quite well studied, in particular monoamine oxidase (MAO), which determines the rate of biosynthesis and breakdown of catecholamines, and catechol methyltransferase, which catalyzes the main pathway of adrenaline conversion, i.e. . O- methylation due to S-adenosylmethionine. We present the structure of the two final decomposition products
34. Glucagon and insulin. Chemical nature, biosynthesis of insulin. The mechanism of action of these hormones at the molecular level. Their role in regulating the metabolism of carbohydrates, fats, and amino acids. Biochemical disorders in diabetes mellitus.
Insulin, which gets its name from the name of the pancreatic islets. The insulin molecule, containing 51 amino acid residues, consists of two polypeptide chains connected to each other at two points by disulfide bridges. In the physiological regulation of insulin synthesis, the concentration of glucose in the blood plays a dominant role. Thus, an increase in blood glucose content causes an increase in insulin secretion in the pancreatic islets, and a decrease in its content, on the contrary, slows down insulin secretion. This feedback control phenomenon is considered one of the most important mechanisms for regulating blood glucose levels. With insufficient insulin secretion, a specific disease develops - diabetes. Physiological effects of insulin: Insulin is the only hormone that reduces blood glucose levels, this is realized through:
§ increased absorption of glucose and other substances by cells;
§ activation of key glycolytic enzymes;
§ increasing the intensity of glycogen synthesis - insulin accelerates the storage of glucose in liver and muscle cells by polymerizing it into glycogen;
§ decrease in the intensity of gluconeogenesis - the formation of glucose from various substances in the liver is reduced
Anabolic effects
§ enhances the absorption of amino acids by cells (especially leucine and valine);
§ enhances the transport of potassium ions, as well as magnesium and phosphate, into the cell;
§ enhances DNA replication and protein biosynthesis;
§ enhances the synthesis of fatty acids and their subsequent esterification - in adipose tissue and in the liver, insulin promotes the conversion of glucose into triglycerides; With a lack of insulin, the opposite happens - mobilization of fats.
Anti-catabolic effects
§ suppresses protein hydrolysis - reduces protein degradation;
§ reduces lipolysis - reduces the flow of fatty acids into the blood.
Glucagon- hormone of alpha cells of the islets of Langerhans of the pancreas. According to its chemical structure, glucagon is a peptide hormone. The glucagon molecule consists of 29 amino acids and has a molecular weight of 3485. The primary structure of the glucagon molecule is as follows.