Biologically important peptides

Biologically important peptides

Q. 1 Shortest peptide. is:

 A Angiotensin-III 

 B

Angiotensin-IV

 C

Angiotensin-II

 D

Angiotensin-I

Q. 1

Shortest peptide. is:

 A

Angiotensin-III 

 B

Angiotensin-IV

 C

Angiotensin-II

 D

Angiotensin-I

Ans. A:B

Explanation:

Correct Ans–> Angiotensin-III & IV

  • decapeptide has ten amino acids (e.g., gonadotropin-releasing hormone & angiotensin I)., Angiotensin I  officially called proangiotensin, is formed by the action of renin on angiotensinogen.
  • Angiotensin I –> Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu | Val-Ile-..
  • IT is converted to angiotensin II (AII) through removal of two C-terminal residues by the enzyme angiotensin-converting enzyme (ACE), An octapeptide has eight amino acids (e.g., angiotensin II).,primarily through ACE within the lung (but also present in endothelial cells, kidney epithelial cells, and the brain).
  • Angiotensin II ( Asp-Arg-Val-Tyr-Ile-His-Pro-Phe) is degraded to angiotensin III by angiotensinases located in red blood cells and the vascular beds of most tissues. 
  • Angiotensin III –> Asp | Arg-Val-Tyr-Ile-His-Pro-Phe
  • Angiotensin III has 40% of the pressor activity of angiotensin II, but 100% of the aldosterone-producing activity. Increases mean arterial pressure. It is a peptide that is formed by removing an amino acid from angiotensin II by aminopeptidase A
  • It has a half-life in circulation of around 30 seconds, whereas, in tissue, it may be as long as 15–30 minutes.
  • Angiotensin IV –> Arg | Val-Tyr-Ile-His-Pro-Phe
  • It is a hexapeptide that, like angiotensin III, has some lesser activity. Angiotensin IV has a wide range of activities in the central nervous system.

So to conclude this Angiotensin III & IV is right answer

  • Angiotensin-(3-4) (Ang-(3-4) or Val-Tyr) is the shorter angiotensin (Ang) II-derived peptide, formed through successive hydrolysis that culminates with the release of Val-Tyr as a dipeptide. It is formed both in plasma and in kidney from Ang II and Ang III, and can be considered a component of the systemic and organ-based renin-angiotensin system. It is potently antihypertensive in humans and rats, and its concerted actions on proximal tubule cells culminate in the inhibition of fluid reabsorption, hyperosmotic urinary excretion of Na+. At the renal cell signaling level, Ang-(3-4) counteracts Ang II-type 1 receptor-mediated responses by acting as an allosteric enhancer in Ang II-type 2 receptor populations that target adenosine triphosphate-dependent Ca2+ and Na+ transporters through a cyclic adenosine monophosphate-activated protein kinase pathway.

Q. 2 Which of the following is not a peptide/protein

 A

Growth hormone

 B

Insulin

 C

PTH

 D

Glucocorticoids

Ans. D

Explanation:

Ans. is ‘d’ i.e., Glucocorticoids

Glucocorticoids are a class of corticosteroids, which are a class of steroid hormones. Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor that is present in almost every vertebrate animal cell.


Q. 3

Bond involved in formation of primary structure of protein/polypeptide ‑

 A

Hydrogen

 B

Peptide

 C

Disulfide

 D

A and B both

Ans. D

Explanation:

Ans: D.  A and B both

Bonds of Primary structure: Covalent bond i.e. Peptide bond

Features Of Peptide Bond:

  • It is Trans in configuration
  • It is neither completely single bond nor completely double bond, it is a Partial double bond
  • It is Polar.
  • It is Uncharged
  • It is a Planar.
  • CO-NH is going to be in one plane (2D )and the R and H group will be protruding outside. 

Q. 4 The enzyme involved in initiation of peptide chain synthesis-

 A

Topoisomerase

 B

Transformylase

 C

RNA polymerase

 D

Peptidyl transferase

Ans. B

Explanation:

Ans. ‘B’ Transformylase

Steps in eukaryotic translation (protein synthesis)

There are three major steps, in protein synthesis (translation):- (i) Initiation, (ii) Elongation; and (iii) Termination.

  • In prokaryotes and in mitochondria, the first amino acid methionine is modified by formylation, i.e. the initiator tRNA carries an N-formylated methionine. The formyl group is added by the enzyme transformylase (formyl-transferase).
  •  In Eukaryotes, the initiator tRNA carries a methionine that is not formylated.

Q. 5

All the following are peptide based except

 A ACTH

 B GnRH

 C

Thyroxin

 D

TRH

Ans. C

Explanation:

Ans. is ‘c’ i.e., Thyroxin 


Q. 6

True about peptide bond formation:

 A

The NH2 group of new aminoacyl t -RNA at A site combine with the – COOH group of Met-t -RNA occupying the ‘P’ site

 B

The NH2 group of new aminoacyl t – RNA at ‘P’ site combine with the – COOH group of Met-t-RNA occupying the ‘A site

 C

Reaction is catalyzed by peptidyl transferase

 D

Peptide bond formation require energy

Ans. A:C

Explanation:

Ans: a. The NH2  and  c. Reaction…[Ref Harper 30th/422-25, 28th/359-66; Lippincott 4th/438-42; Chatterjea te• Shinde 7th/248-501]

  • The a-amino group of the new aminoacyl-tRNA in the A site carries out a nucleophilic attack on the esterified carboxyl group of the peptidyl-tRNA occupying the P site (peptidyl or polypeptide site). At initiation, this site is occupied by aminoacyl-tRNA met’.
  • This reaction is catalyzed by a peptidyltransferase, a component of the 28S RNA of the 60S ribosomal subunit. This is another example of ribozyme activity and indicates an important—and previously unsuspected—direct role for RNA in protein synthesis.
  • Because the amino acid on the aminoacyl-tRNA is already “activator no further energy source is required for this reaction. The reaction results in attachment of the growing peptide chain to the tRNA in the A site.


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