MCQ on Amino Acids (Part-4)

Biochemistry MCQ-07: Amino acids are the building blocks of proteins. They are organic compounds that contain both an amino group (-NH2) and a carboxyl group (-COOH) attached to a central carbon atom. There are 22 different types of amino acids that are commonly found in proteins, each with a unique side chain that gives it distinct properties. In addition to their role in protein synthesis, amino acids also play important roles in metabolism, cell signaling, and other biological processes. This the Part-4 of Multiple Choice Questions on Amino Acids with answer key and explanations.

You May also like: Amino Acids MCQ Part-1 | Part-2 | Part-3 | Part-4 | Part-5 |

(1). 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

2). pKa is the measure of a group to __________ proton.
a.       Take up
b.      Release
c.       Combine
d.      Consume

3). Which of the following amino acid bears a guanidine group in the side chain?
a.       Lysine
b.      Arginine
c.       Histidine
d.      Proline

4). The precursor of glycine synthesis in microbes and plants is_______.
a.       Serine
b.      Leucine
c.       Valine
d.      None of these

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5). Single letter code of selenocysteine is _____.

a.       B
b.      J
c.       U
d.      O

6). Which of the following amino acid have an imino group in the side chain?
a.       Proline
b.      Asparagine
c.       Glutamate
d.      Histidine

7). 4-hydroxy proline (a derivative of proline) is abundantly present in _______.
a.       Keratin
b.      Myoglobin
c.       Hemoglobin
d.      Collagen

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8). Desmosine is a complex derivative of five ____________ residues.
a.       Lysine
b.      Arginine
c.       Histidine
d.      Methionine

9). Isoelectric pH is designated as______.
a.      pKa
b.      pI
c.       Pi
d.      None of these

10). Which of the following amino acid is biosynthesized from Ribose 5-phposphate?
a.       Histidine
b.      Serine
c.       Glycine
d.      All of these

11). Amino acid biosynthesized from Pyruvate of glycolysis is _____.
a.       Alanine
b.      Valine
c.       Leucine
d.      All of these

12).  Aromatic amino acids (Phenylalaine, Tyrosine, and Tryptophan) are derived from Phosphoenol pyruvate and __________.
a.       Ribose 5-phosphate
b.      Erythrose 4-phosphate
c.       Oxaloacetate
d.      α-ketoglutarate

13).  Isoleucine is derived from ___________.

a.       Methionine
b.      Threonine
c.       Lysine
d.      Leucine

14).  Blood clotting protein thrombin usually contain which of the following modified amino acid?

a.       4-hydroxy proline
b.      5-hydroxy lysine
c.       6-N-methyl lysine
d.      γ-carboxy glutamate

15).  Cysteine is not an essential amino acid in human, since we have the machinery to synthesize cysteine from other two amino acids namely _______ and serine.

a.      Methionine
b.      Selenocysteine
c.       Citrulline
d.      Hydroxyproline

16). Which of the following contain a disulfide bridge?

a.       Cysteine
b.      Cystine
c.       Methionine
d.      None of these
e.       All of these

17). Which of the following protein contain a modified amino acid – desmosine?

a.       Keratin
b.      Gelatin
c.       Elastin
d.      Collagen

180.  During biosynthesis, Methionine and Threonine are derived from a common intermediate:

a.       Chorismate
b.      Citrulline
c.       Homoserine
d.      Cystathione

19).  6-N-methyl lysine is a derivative of lysine, present in__________.

a.       Keratin
b.      Collagen
c.       Myosin
d.      Myoglobin

20).  A common intermediate branch point in the synthesis of all aromatic amino acids such as Tryptophan, Phenylalanine and Tyrosine is _____.

a.       Homoserine
b.      Chorismate
c.       Cystathione
d.      None of these

21). Sarcosine, a ubiquitous non protenacius amino acid in animals and plants is ____.

a.       N-methylglycine
b.      N-methylvaline
c.       N-methylserine
d.      N-methylmethionine

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Answers and Explanations:

1. Ans. (a). Carboxyl group

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.

2. Ans. (b). Release

pKa is the negative logarithm of Ka. Ka is the dissociation constant of an ionization reaction such as the ionization of acetic acid. Ka is similar to equilibrium constant of any chemical reaction and 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 i.e., reciprocal of ka).

3. Ans. (b). Arginine

4. Ans. (a). Serine

5. Ans. (c). U

6. Ans. (a). Proline

7. Ans. (d). Collagen

8. Ans. (a). Lysine

9. Ans. (b). pI

10. Ans. (a). Histidine

11. Ans. (d). All of these

12. Ans. (b). Erythrose 4-phosphate

13. Ans. (b). Threonine

14. Ans. (d) γ-carboxy glutamate

15. Ans. (a). Methionine

Methionine provide sulfur

Serine provide the backbone of cysteine

16. Ans. (b). Cystine

17. Ans. (c). Elastin

18. Ans. (c). Homoserine

19. Ans. (c). Myosin

20. Ans. (b). Chorismate

21. Ans. (a). N-methylglycine

You May also like: Amino Acids MCQ Part-1 | Part-2 | Part-3 | Part-4 | Part-5 |


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