Biochemistry Interview Questions and Answers for freshers focuses on “Reversible Binding of a Protein to a Ligand: Oxygen-Binding Proteins”.
1. Which of the following is false?
A. Heme consists of a complex organic ring structure, protoporphyrin
B. Protoporphyrin is bound to a single iron atom in its Fe+3 state
C. Iron atom has 6 coordination bonds
D. Heme is found in a number of oxygen transporting proteins
Answer: B
Clarification: Protoporphyrin is bound to a single iron atom in its Fe+2 state.
2. Myoglobin is particularly abundant in ________
A. Nerves
B. Muscles
C. Blood cells
D. Skin
Answer: B
Clarification: As a transport protein, it facilitates O2 diffusion in muscle.
3. His93 is also called ________
A. His F8
B. His F7
C. His F6
D. His F5
Answer: A
Clarification: His93, the 93rd amino acid residue from the amino-terminal end of the myoglobin polypeptide sequence is also called His F8, the 8th residue in α helix F.
4. Which of the following is a correct relation?
A. Ka [L] = [PL] ⁄ [P]
B. Ka [L] = [P] ⁄ [PL]
C. Ka [L] = [PL] × [P]
D. Ka [PL] = [L] ⁄ [P]
Answer: A
Clarification: The term Ka is an association constant
Ka [L] = [PL] ⁄ [P] [L].
5. Which of the following is a correct relation?
A. Kd [L] = [PL] ⁄ [P]
B. Kd [L] = [P] ⁄ [PL]
C. Kd [L] = [PL] × [P]
D. Kd [PL] = [L] ⁄ [P]
Answer: A
Clarification: The term Kd is a dissociation constant
Ka [L] = [P] [L] ⁄ [PL].
6. Myoglobin binding of O2 depends on ___________
A. Hemoglobin concentration
B. O2 concentration and affinity of myoglobin for O2
C. Ka
D. Kd
Answer: B
Clarification: Myoglobin binding of O2 depends on pO2 and its affinity for O2.
7. In the binding of oxygen to myoglobin, the relationship between the concentration of oxygen and the fraction of binding sites occupied can best be described as ___________
A. Hyperbolic
B. Linear with a negative slope
C. Linear with a positive slope
D. Parabolic
Answer: A
Clarification: The equation θ=(pO2)/(pO2 +P50) is of the form y = x/(x+z) which describes hyperbola.
8. Myoglobin and the subunits of hemoglobin have ___________
A. Very different primary and tertiary structures
B. Very similar primary and tertiary structures
C. Very similar primary structures, but different tertiary structures
D. Very similar tertiary structures, but different primary structures
Answer: D
Clarification: Hemoglobin is a tetramer and myoglobin is a monomer.
9. The interactions of ligands with proteins are ___________
A. Relatively nonspecific
B. Relatively rare in biological systems
C. Usually irreversible
D. Usually transient
Answer: D
Clarification: The interactions of ligands with proteins are reversible and transient.
10. When oxygen binds to a heme-containing protein, the two open coordination bonds of Fe2+ are occupied by___________
A. One O atom and one amino acid atom
B. One O2 molecule and one amino acid atom
C. One O2 molecule and one heme atom
D. Two O atoms
Answer: B
Clarification: The two coordination bonds to Fe2+ perpendicular to the porphyrin ring system. One of these bonds is occupied by a Hys residue and the other bond by O2.
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