MCQ on proteins with explanation set 1

MCQ on proteins with explanation set 1

Q) Hemoglobin shows sigmoidal curve for oxygen saturation. What is the shape of curve for myoglobin oxygen binding?

a) Linear
b) Hyperbolic
c) Sigmoidal
d) Bell shaped

Answer: Option b

Myoglobin is the oxygen storage protein of muscles, the oxygenated myoglobin it is responsible for the deep red colour of muscles.

Q) What is the force among the following that is primarily responsible for stabilizing the tertiary structure of globular proteins?

a) Disulfide bonding
b) The hydrophobic effect
c) Hydrogen bonding
d) Ionic interactions

Answer: Option b

Q) Cα-Cα distance plant might be useful in

a) Identifying secondary structure in proteins
b) Identifying globular domains in a protein
c) Identifying active sites in enzymes
d) For docking of inhibitors on protein’s surface

Answer: option b

Q) Isoelectric point of lysozyme is 9.2. When the enzyme solution at this pH in water was titrated with HCl to give a pH of 5, it was observed that six ionized glutamic acid side chains got protonated. The net charge on the enzyme at pH 6 would therefore be

a) +5
b) +6
c) -5
d) -6

Answer: option b

Q) In peptides the values of dihedral angle phi is based on rotation around

a) N – Cα bond
b) Cα – C bond
c) C – N bond
d) N – H bond

Answer: option A

Q) Which of the following amino acid sequences belong to collagen fibres?

Gly-Ala-Gly-Thr-Gly-Ala-Gly-Thr-Gly-Ala-Gly-Thr
b. Gly-Ala-Glu-Ser-Leu-Gly-Ala-Glu-Ser-Leu-Gly-Ala
c. Gly-Ala-Pro-Gly-Pro-Pro-Gly-Thr-Pro-Gly-Ala-Pro
d. Gly-Ala-Glu-Ser-Leu-Gly-Asn-Gly-Ala-Gly-Ala-Glu-Ser-Leu-Gly-Asn

Answer: option c

Q) In proteins, hydrogen bonds forms as follows: Donor (D)-H— Acceptor (A). Hydrogen bond is more favourable if the angle between D-H and A is:

a) <900
b) 1800
c) >1800
d) 1200

Answer: Option b

 Hydrogen bond: A very weak bond formed by the electrostatic attraction between hydrogen which is covalently bonded to an electro negative atom, such as oxygen or nitrogen, to other electro negative atom. Hydrogen bond is most favourable and strong when all the three bonded atoms are in a straight line (1800). When hydrogen bonds are structurally constrained, the geometry will loose and the bonds become weaker.

Q) Globular proteins when treated with organic solvent get denatured. The main interaction which is affected on treatment with chloroform is

a) Hydrogen bonds

b) Covalent bonds

c) Ionic interactions

d) Hydrophobic interactions

Answer: Option D

Reason: The hydrophobic interaction is the most important interaction responsible for proper folding of a protein that makes the protein functional

Q) In an alpha helical polypeptide, the backbone hydrogen bonds are between
NH of n and CO of n+4 amino acids.
b. CO of n and NH of n+3 amino acids.
c. CO of n and NH of n+4 amino acids.
d. NH of n and CO of n+3 amino acids.

Answer: Option A

Q) Which of the following is not true about secondary protein structure?
a) The hydrophilic/hydrophobic character of amino acid residues is important to secondary structure.
b) The ability of peptide bonds to form intramolecular hydrogen bonds is important to secondary structure.
c) The alpha helix, beta pleated sheet and beta turns are examples of protein secondary structure.
d) The steric influence of amino acid residues is important to secondary structure.

Answer: Option A

Explanation: The hydrophilic / hydrophobic character of amino acid residues is important to protein tertiary structure rather than to secondary structure. In secondary structure, it is the steric size of the residues that is important and residues are positioned to minimize interactions between each other and the peptide chain.

 

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