BIOCHEMISTRY in Questions and Answers - Alimov A.M. - 2016

SECTION 8. PROTEIN AND AMINO ACID METABOLISM

Question 1. Which Amino Acids are called essential?

Answer. Amino acids that cannot be synthesized in the Human and Animal body.

Question 2. What is nitrogen balance?

Answer. Nitrogen balance is The ratio of assimilated nitrogen to nitrogen excreted as End products of METABOLISM: X=Nassimilated / Nend products of metabolism.

Question 3. What types of nitrogen balance exist?

Answer: 1. Positive — when the assimilation of nitrogen/amino acids/ exceeds the amount excreted in urine and feces as ionic products of protein and Amino Acid Catabolism.

2. Negative — The amount of nitrogen assimilated is less than that excreted as end products of metabolism.

3. Nitrogen equilibrium. Characterized by equal amounts of assimilated nitrogenous substances and those excreted as end products of metabolism.

Question 4. Which Proteins are considered biologically complete?

Answer: Proteins that contain all Essential Amino Acids and are easily assimilated by the body. These are mainly proteins of animal origin.

Question 5. What is proteolysis?

Answer: Proteolysis is The breakdown of protein into free amino acids under the action of Proteolytic Enzymes.

Question 6. Which enzymes catalyze Protein Digestion in The Stomach?

Answer: Pepsin, Chymotrypsin.

Question 7. Which enzymes break down proteins into Polypeptides in the intestine?

Answer: Elastase, pepsin, chymotrypsin.

Question 8. Name the proenzymes of pepsin and Trypsin and their activators?

Answer: Pepsin and trypsin. Pepsinogen is activated by Hydrochloric acid and gastric juice. Trypsin is activated by enteropeptidase.

Question 9. Where are the products of protein putrefaction formed in the intestine detoxified?

Answer. In the Liver

Question 10. What is the detoxification pathway for indole, a breakdown product of Tryptophan formed by the action of intestinal microflora enzymes?

Answer:

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Question 11. What is the source of amino acids in the body?

Answer: 1. Breakdown of dietary proteins

2. Intracellular proteolysis

3. Synthesis of non-essential amino acids within The Cell

Question 12. What is the Biological Role of amino acids?

Answer. 1. Amino acids serve as monomers for protein molecules and Peptides

2. They are precursors of:

a) nitrogenous bases;

b) Porphyrins;

c) glucose;

d) Hormones—thyroxine, adrenaline, melatonin

e) biogenic amines

Question 13. How do amino acids break down within the cell?

Answer. 1. Deamination

2. Decarboxylation

Question 14. What types of deamination exist?

Answer: 1. Direct

2. Indirect

Question 15. What are the pathways of direct AMINO ACID DEAMINATION?

Answer: 1. Non-oxidative

2. Oxidative

Question 16. What is indirect deamination?

Answer: Indirect deamination consists of two reactions:

1. Transamination, involving The transfer of an NH₂ group from any amino acid to 2-oxoglutarate to form glutamate

2. Oxidative Deamination of glutamate catalyzed by Glutamate dehydrogenase

Question 17. Which coenzyme is required for transamination reactions?

Answer: Pyridoxal phosphate

Question 18. What is the Biological Significance of transamination?

Answer. 1. Non-essential amino acids are synthesized

2. Any amino acid undergoes deamination

3. Deamination occurs without releasing NH₃⁺ into the environment

Question 19. What are the sources of ammonia in tissues?

Answer: Deamination of:

1. Amino acids

2. Biogenic amines

3. Glutamine and asparagine

4. Nitrogenous bases

Question 20. What are the Pathways of ammonia detoxification in the body?

Answer: 1. Urea synthesis in the liver

2. Synthesis of Glutamine and asparagine

3. Reductive amination

4. Synthesis of ammonium salts

Question 21. What compounds are formed As a result of AMINO ACID DECARBOXYLATION?

Answer: Biogenic amines

Question 22. How are biogenic amines detoxified?

Answer: With the participation of monoamine oxidases and diamine oxidases, yielding corresponding aldehydes and subsequently acids. The detoxification process takes place in liver microsomes

Question 23. What is the biological role of histamine?

Answer: 1. Stimulates HCl secretion in the stomach

2. Dilates capillaries and lowers Blood pressure

3. Mediates allergic and immune reactions

Question 24. What is the biological action of serotonin?

Answer: 1. It acts as an excitatory neurotransmitter in the Central Nervous system

2. Serotonin is a precursor to the hormone melatonin

3. It induces contraction of the smooth Muscles of the Uterus, intestines, Bronchi, and Blood Vessels

4. It serves as a mediator of inflammation and pain

5. It accelerates blood clotting time

Question 25. What nitrogen sources are used in urea Biosynthesis?

Answer: 1. One nitrogen atom is provided by NH₃, which reacts with СО₂ to form carbamoyl phosphate

2. The second nitrogen atom is supplied by any amino acid via the amino group of aspartate

Question 26. In which organ does urea synthesis take place?

Answer: Primarily in the liver, after which urea enters the blood and is excreted in the urine

Question 27. How is ammonia detoxified in the central nervous system?

Answer: Through the synthesis of asparagine and glutamine, which easily cross the blood-Brain barrier and are transported via the bloodstream to the Kidneys and liver

Question 28. How does glutamine breakdown occur in the kidneys?

Answer: Glutamine is deamidated by glutaminase; the released NH₃ binds H+ to form an ammonium ion (NH₃⁺H⁺ —> NH₄⁺). This process maintains acid-base balance during acidosis and conserves Na⁺ in the body

Question 29. What is The Fate of the nitrogen-free residues of amino acids?

Answer: The carbon skeletons (nitrogen-free residues) can be converted into:

1. Glucose (glucogenic amino acids)

2. Acetoacetate (ketogenic amino acids)

3. Acetyl-CoA, which is used to synthesize Fatty acids and Cholesterol

Question 30. Which amino acids are ketogenic?

Answer: Leucine, isoleucine, phenylalanine, Tyrosine, Lysine, tryptophan

Question 31. Which amino acids are involved in creatine synthesis?

Answer: Glycine, Arginine, Methionine

Question 32. Which enzyme is involved in The formation of creatine phosphate?

Answer: Creatine kinase. The resulting creatine phosphate is a high-energy compound that ensures rapid resynthesis of ATP in Muscle and brain tissue.

Question 33. In the synthesis of which compounds does glycine participate?

Answer: Porphyrins, purine and nitrogenous bases, Glutathione, creatine, conjugated Bile acids, and Collagen.

Question 34. What substances are formed from Phenylalanine and Tyrosine?

Answer: 1. Dopamine, adrenaline, and noradrenaline (Nervous Tissue, Adrenal Glands)

2. Melanins (melanocytes)

3. Thyroxine (Thyroid Gland)

4. Acetoacetate and fumarate (liver)

Question 35. What is albinism?

Answer: Albinism is a disorder in the formation of pigments from dihydroxyphenylalanine during tyrosine degradation.

Question 36. What substances are formed from tryptophan?

Answer: Serotonin, NAD+