MCQ on aminoacid with explanation set 3

MCQ on aminoacid with explanation set 3

Q) The following is the amino acid sequence of an alien polypeptide: ‘AGQHIKXSKPWYVGLBUFF’. The ‘X’ in the given sequence represents ___________.

a) Asparagine
b) Isoleucine
c) An ambiguous amino acid
d) An unknown amino acid

Answer: option d

Q) _____ is an exclusively ketogenic amino acid in human.

a) Valine
b) Methionine
c) Leucine
d) Proline

Answer: option c


Leucine and lysine are the two amino acids in human which are exclusively ketogenic.

Q) The pair of aminoacids which does not undergo post translational modification is

A) Asn – His

B) Tyr – Ser

C) Asn – Ser

D) Ala – Gly

Answer: option d

Q) Which of the following aminoacids has the highest quantum yield in aqueous solution?

A) Tyrosine

B) Tryptophan

C) Histidine

D) Phenylalanine

Answer: option B

Q) Which group of a fully protonated glycine (NH3+ – CH2 – COOH) first release a ‘proton’ when it is titrated against – OH- ions?

a) Carboxyl group
b) Amino group
c) Both at the same time
d) It cannot be predicted

Answer: option a

Explanation: First COOH group will release H+ ions and it will combine with OH- ions to form water. Only after complete ionization of all the COOH groups, the NH3+ release H+ions.

Q) pKa is the measure of a group to __________ proton.

a) Take up
b) Release
c) Combine
d) Consume

Answer: option b


  • pKa is the negative logarithm of Ka.
  • Ka is the dissociation constant of an ionization reaction such as the ionization of acetic acid.
  • it is calculated by dividing the concentration of products divided by concentration of its reactants.
  • Ka denotes the strength of an acid. Strong acids will have a higher value of Ka where as a weaker acid will have a lesser values of Ka.
  • The stronger the tendency to dissociate a proton, the stronger is the acid and the lower its pKa (Since pKa is negative logarithm of Ka e., reciprocal of ka).

Q) Which amino acid residue is most likely to be found in the interior of a water soluble globular protein?

a) Ser

b) Arg

c) Asp

d) Val

Answer: option d


 Valine: hydrophobic amino acid prefer interior of the globular protein

Arginine and asparagine are hydrophilic and tend to be in the exterior.

Q) Which one of the following amino acids has a higher propensity for cis peptide bond  formation?

a) Histidine
b) Cysteine
c) Glycine
d) Proline

Answer: option d

Q) Carnosine is a dipeptide of histidine and _____.

a) β-histidine
b) β-alanine
c) β-lysine
d) α-lysine

Answer: option b


Carnosine:  dipeptide of histidine and β-alanine( an antioxidant present in muscle cells and brain cells of human).

β-alanine is naturally occurring β-amino acid (amino group is at the β position not in the α position)

Q) Which of the following is an example for a bio-plastic?

a) Polyaspartate
b) Polyglutamate
c) Poly-L-lysine
d) All of these

Answer: option a


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