amino acid qna

1. Which of the following enzymes catalyses the attachment of an amino acid to t-RNA ?

A) aminoacyl tRNA synthetase
B) tRNA ligase
C) Ribosome
D) A) and B) both

... Answer is D)
aminoacyl tRNA synthetase also calld tRNA ligase which catalyses the attachment of an amino acid to tRNA.

2. which part of an amino acid is always acidic in nature ?

A) COOH
B) NH₂
C) side chain (R)
D) all of the above

... Answer is A)
carboxyl (COOH) group of an amino acid is always acidic.

3. Which of the following is not attached to the central carbon atom of an amino acid

A) COOH
B) O
C) H
D) NH₂

... Answer is D)
The central carbon atom of an amino acid is attached with an amino group(NH₂), caboxyl group(COOH), R side chain and hydrogen atom. there is no any Oxygen molecule which attached with central carbon atom .

4. which one of the following amino acids possesses a net charge at pH 7 ?

A) Proline
B) Leucine
C) Aspartate
D) Valine

... Answer is C)
Because of the presence of an carboxy group in the side chain, the dicarboxylic (also called acidic) amino acids, aspartic acid exhibit a net negative charge at pH 7; these forms of the amino acids is called aspartate.

5. Which of the following amino acids actually has a secondary amino group ?

A) Lysine
B) Proline
C) Alanine
D) Valine

... Answer is B)
Proline is the only amino acid in which the side chain loops back to reattach to the main polypeptide chain. This has two main consequences:

1). Proline has a secondary amino group instead of the primary amino group present in all the other amino acids. It thus behaves differently in many of the reactions used in protein chemistry.

2). Proline forces a bend in the polypeptide backbone and can thus disrupt an a - helix and axert other constraints on the folding of a protein.