This set of Life Sciences Multiple Choice Questions & Answers (MCQs) focuses on “Amino Acids and Proteins”.
1. The general structure of all amino acids are same except for ___________
a) Lysine
b) Glycine
c) Proline
d) Alanine
View Answer
Explanation: In general, all α-amino acid consists of an amino group, a hydrogen atom, and a distinctive side chain, all bonded to α-carbon. Proline is the only amino acid which has a cyclic distinctive side chain which differs from all other amino acids.
2. An amino acid is an amphoteric molecule.
a) True
b) False
View Answer
Explanation: When an amino acid dissolved in water, it acts as acid or base and called as the zwitterion or dipolar ion. Hence, an amino acid is an amphoteric molecule.
3. Which of these amino acids are not optically active?
a) Cysteine
b) Lysine
c) Arginine
d) Glycine
View Answer
Explanation: When a carbon atom has four different constituents, it is said to be chiral. All amino acids have chiral carbon except glycine and hence they are optically active.
4. Which of these are used to measure optical activity?
a) Polarimeter
b) Planometer
c) Psychrometer
d) Photometer
View Answer
Explanation: Polarimeter is used to measure the rotation of polarized light while planometer is used for area measurement and psychrometer measure humidity. Similarly, photometer measures illuminance or irradiance.
5. A solution of L-alanine (4.0g/50 ml of 6 N HCl) has a rotation of +1.61° in a 2dm polarimeter tube. Calculate the specific rotation of L-alanine in 6 N HCl.
a) +15.1°
b) +10.1°
c) +11.1°
d) +16.1°
View Answer
Explanation: [α] = Α°/ l×C; +1.61/2×0.08
[α]= +10.1°.
6. Name the amino acid, which exists in two non-superimposable mirror images of each other.
a) Epimer
b) Anomer
c) Enantiomer
d) Chiral carbon
View Answer
Explanation: When an amino acid with a chiral carbon exists in two non-superimposable mirror images of each other, it is called enantiomers. It can be easily identified by its configuration.
7. Which of these are rare amino acid in a protein?
a) Leucine and serine
b) Lysine and glutamic acid
c) Tryptophan and methionine
d) Leucine and lysine
View Answer
Explanation: Tryptophan and methionine are rare in protein as they have only one codon for each while lysine, leucine, serine and glutamic acid have more than one codon for each protein.
8. In which amino acid Imidazole group, an aromatic ring found?
a) Lysine
b) Arginine
c) Histidine
d) Glutamate
View Answer
Explanation: Histidine contains imidazole group which can be uncharged or positively charged, depending on its local environment. Lysine & arginine contains positively charged R group while glutamate has negatively charged R group.
9. What is the maximum wavelength that Tryptophan and tyrosine absorb?
a) 280nm
b) 260nm
c) 257nm
d) 230nm
View Answer
Explanation: Tryptophan, tyrosine, and phenylalanine are aromatic amino acids and absorbs ultraviolet light (UV). Absorption at 280nm is used for quantification and detection of purified proteins. The absorbance of proteins is dependent on number and position of aromatic amino acid residues.
10. How is the secondary structure of a protein stabilized?
a) Van der wall forces
b) Hydrogen bonding
c) Covalent bond
d) Hydrophobic bond
View Answer
Explanation: Hydrogen bonding can bring together two chains which are at distance in terms of a sequence. Depending on hydrogen bonding, proteins have two structural conformations α-helix and β-sheets.
11. How many amino acid residues are there in per turn of α-helix?
a) 3.6
b) 4.6
c) 3.0
d) 2.5
View Answer
Explanation: Length of α-helix is usually 10-15 amino acid residue and there are 3.6 amino acid residues per turn of the helix. A single turn of α-helix has 13 atoms due to this α-helix is also referred as 3.613 helix.
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