250+ TOP MCQs on Structure Function Relationships – Zinc Fingers and Answers

Protein Engineering Multiple Choice Questions on “Structure Function Relationships – Zinc Fingers”.

1. Regulatory proteins have only protein-DNA interacting domains.
A. True
B. False
Answer: B
Clarification: The above statement is false. The regulatory proteins contain domains not only for DNA binding but also for protein-protein interaction. Examples include many eukaryotic transcription factors that function as gene activators.

2. Which among the following motifs contain a positively charged ion?
A. Leucine zippers
B. H-T-H motif
C. Homeobox
D. Zinc fingers
Answer: D
Clarification: The zinc finger DNA-binding motif contains a positively charged zinc ion. There is a single Zn⁺² ion in the core structure of the zinc motif. This Zn⁺² ion is coordinated with four amino acid residues.

3. The positively charged Zn⁺² ion in the zinc finger interacts directly with the negatively charged phosphate in DNA.
A. True
B. False
Answer: B
Clarification: The above statement is false. In zinc fingers, the elongated loop is held together at the base by a single Zn⁺² ion. The Zn⁺² ions do not itself interact with DNA.

4. Zn⁺² ions in zinc fingers are coordinated to which amino acid residues?
A. 2 Met and 2 Cys
B. 4 Val or 2 Met and 2 Cys
C. 2 Ala and 2 Gly
D. 4 Cys or 2 Cys and 2 His
Answer: D
Clarification: The zinc ion is coordinated to four of the following residues: 4 Cys or 2 Cys and 2 His. This coordination of zinc with the amino acids stabilizes this small structural motif. Thus, the Zn⁺² ions do not directly interact with the DNA.

5. What is the average length of the elongated loop in zinc fingers?
A. 20 amino acid residues
B. 10 amino acid residues
C. 40 amino acid residues
D. 30 amino acid residues
Answer: D
Clarification: The average length of the elongated loop in zinc fingers is 30 amino acid residues. This loop is held together at the base by a single Zn⁺² ion. These ions form a coordination bond with the amino acid residues in the loop.

6. The interaction of a single zinc finger with DNA is typically very strong.
A. True
B. False
Answer: B
Clarification: The above statement is false. The interaction of a single zinc finger with DNA is typically weak and many DNA-binding proteins have multiple zinc fingers that substantially enhance binding by interacting simultaneously with the DNA.

7. Zinc fingers can also function as which of the following?
A. Lipid-binding motif
B. Carbohydrate-binding motif
C. Ribosome-binding motif
D. RNA-binding motif
Answer: D
Clarification: Zinc fingers can also function as an RNA-binding motif. E.g. in certain proteins that bind eukaryotic mRNAs and act as translational repressors. Zinc fingers do not function as a lipid-binding motif, carbohydrate-binding motif, and ribosome-binding motif.

8. Zinc fingers in found in many eukaryotic DNA-binding motifs.
A. False
B. True
Answer: B
Clarification: The above statement is true. Zinc fingers in found in many eukaryotic DNA-binding motifs. There are few known examples of the zinc finger motifs in bacterial proteins.

9. Which of the following is not true for zinc fingers?
A. It contains a beta-sheet domain
B. It contains an alpha-helix domain
C. It contains Zn⁺² ion
D. It contains Ca⁺² ion