MCQ on aminoacid with explanation set 5

MCQ on aminoacid with explanation set 5

Q) Which of the following enzyme contain Selenocysteine?

a) Nitrate reductase
b) Catalase
c) Glutathione peroxidase
d) All of these

Answer: option c

Explanation:

  • Selenocysteine (Sec) is considered as the 21stprotein coding amino acid.
  • It is a rare amino acid containing Selenium as selenol group (SeH).
  • Selenocysteine is coded by UGA codon, one of the stop codon, by a mechanism called translational recoding.

Example of proteins containing selenocysteine:

glutathione peroxidases, thioredoxin reductases, formate dehydrogenases, glycine reductases, selenophosphate synthetase and methionine-R-sulfoxide reductase.

Q) Which of the following is a glucogenic amino acid?

a) Glycine
b) Proline
c) Both (a) and (b)
d) All of these

Answer: option d

Explanation:

  • Glucogenic amino acids: Those amino acids which are converted into glucose by gluconeogenesis during fasting and starvation.
  •  Except Leucine and Lysine, all amino acids are glucogenic.
  • Ketogenic amino acid: Amino acids which cannot be converted into glucose during catabolism. These amino acids are directly converted into Acetyl CoA through ketogenesis and enters into Kreb’s cycle for energy release
  • Leucine and Lysine are exclusively ketogenic amino acids.
  • Some amino acids such as Isoleucine, Threonine, Phenylalanine, Tyrosine and Tryptophan are both glucogenic and ketogenic.

Q) Bacteria prefer to use the codon CGA instead of AGA to code for Arginine. This is an example for _____.

a) Second genetic code
b) Nullomers
c) Transcriptional decoding
d) Allomers

Answer: option b

Explanation:

Nullomer: They are codons of natural amino acids but are generally not present in the genome of the organism even though these codons are theoretically possible. For example, AGA and CGA are the codons for arginine in all organisms. However, in most bacterial species the codon AGA is not used for coding arginine and if we artificially substitute AGA for CGA, it will be lethal to the organism.

Q) Histones are rich in__________.

a) Lysine
b) Arginine
c) Histidine
d) Lysine and Arginine

Answer: option d

Explanation:

  • Histones are proteins of eukaryotes which help in the packing of DNA in nucleosome.
  • Histones are highly basic in charge since they are rich in basic (positively charged) amino acids such as lysine and arginine.
  • Positive charges of histones stabilize the negatively charged DNA by charge-charge interactions.
  • Chemical modification of histones (acetylation and methylation) helps in the winding or unwinding of DNA during transcription, replication and repair.

Q) Taurine, the major constituent of bile, is derived from____.

a) Cysteine
b) Methionine
c) Tryptophan
d) Lysine

Answer: option a

 Explanation:

Taurine (2-aminoethanesulfonic acid) is a major constituent of bile in human. It is very essential for proper cardiovascular functions, development and functions of skeletal muscles, retina and central nervous system.

Q) Which of the following amino acid is more likely to occupy the interior of a globular protein?

a) Methionine
b) Aspartate
c) Lysine
d) All of these

 Answer: option a

Explanation:

  • Hydrophilic and hydrophobic interactions of amino acids play a crucial role in determining protein’s three dimensional conformations.
  • In globular proteins, the hydrophobic residues occupy the interior portion whereas hydrophilic residues stay exterior and form a shell by interacting with water.
  • This hydrophilic and hydrophobic interaction of amino acids with water assists the folding of polypeptide to globular manner in globular proteins.

Q) Glycine is _____.

a) A stimulatory neurotransmitter
b) An inhibitory neurotransmitter
c) Not act acting as a neurotransmitter
d) Both (a) and (b)

Answer: option b

Q) Which of the following amino acid contain a thioether group in the side chain?

a) Cysteine
b) Cystine
c) Glycine
d) Methionine

Answer: option d

Explanation:

Methionine (first amino acid in protein synthesis) is another sulfur containing amino acid. Sulfur in methionine is in the form of methyl thioether (C – S – C). Thioether group is highly non polar.

Q) Tryptophan and tyrosine strongly absorbs UV light because of

a) Delocalized pie electrons
b) Long aromatic rings
c) Hydroxyl and NH groups
d) Stable pie electrons

 Answer: Option A

Q) When alanine and lysine form an amide bond, the product would be

a) a dipeptide
b) alanyllysine
c) lysylalanine
d) all of the above

Answer: Option d

Leave a Reply

Your email address will not be published. Required fields are marked *