Question 1
Considering the specificity of the protein-DNA interaction in the case of regulatory proteins it can be concluded that there is a particular amino acid-base code.
A. True
B. False
View Answer
Answer: Option B
Explanation:
The above statement is false. Examination of the structure of many DNA-binding proteins has shown that a protein can recognize each base pair in more than one way. This leads to the conclusion that there is no simple amino acid-base code.
Question 2
From the H-T-H motif, only one of the two α-helical segments is called the recognition helix.
A. False
B. True
View Answer
Answer: Option B
Explanation:
The above statement is true. From the H-T-H motif, only one of the two α-helical segments is called the recognition helix, because it usually contains many of the amino acids that interact with the DNA in a sequence-specific manner.
Question 3
The H-T-H structure is inherently very stable.
A. True
B. False
View Answer
Answer: Option B
Explanation:
The above statement is false. The structure is not generally stable by itself; it is simply the reactive portion of a somewhat larger DNA-binding domain. Hence, the H-T-H structure is not inherently stable.
Question 4
The lac repressor has which of the following DNA-binding motifs?
A. Leucine zippers
B. Zinc fingers
C. Homeodomain
D. H-T-H motif
View Answer
Answer: Option D
Explanation:
The lac repressor has H-T-H DNA-binding motifs. The lac repressor is a tetramer. It contains two dimers tethered together. Hence, in total it has 4 H-T-H DNA-binding motifs.
Question 5
What are the genes that regulate the development of body patterns called?
A. Developmental genes
B. Growth genes
C. Activator genes
D. Homeotic genes
View Answer
Answer: Option D
Explanation:
The genes that regulate the development of body patterns are called homeotic genes. Homeodomain was first discovered in homeotic genes. Mutations in the homeotic genes are lethal.
Question 6
What is the average length of the H-T-H motif?
A. 30 amino acid residues
B. 50 amino acid residues
C. 100 amino acid residues
D. 20 amino acid residues
View Answer
Answer: Option D
Explanation:
The average length of the H-T-H motif is 20 amino acid residues. It contains two α-helices separated by a beta-turn. The length of this beta-turn is usually very short.
Question 7
What is the average length of the α-helical segments in the H-T-H motif?
A. 13 – 15 amino acid residues
B. 11 – 19 amino acid residues
C. 10 – 15 amino acid residues
D. 7 – 9 amino acid residues
View Answer
Answer: Option D
Explanation:
The average length of the α-helical segments in the H-T-H motif is about 7 – 9 amino acid residues. The H-T-H motif contains two short-helices. It is present in the DNA-binding domain of many bacterial regulatory proteins.
Question 8
What is the DNA sequence that encodes the homeodomain known as?
A. Zinc fingers
B. H-T-H motifs
C. Leucine zippers
D. Homeobox
View Answer
Answer: Option D
Explanation:
Homeobox is the DNA sequence that encodes the homeodomain. The DNA binding segment of homeodomain is related to the helix-turn-helix motif.
Question 9
Which among the following is not a DNA-binding motif?
A. H-T-H
B. Zinc fingers
C. Homeodomain
D. Homeobox
View Answer
Answer: Option D
Explanation:
Homeobox is not a DNA-binding motif. The DNA sequence that encodes homeodomain is known as the homeobox. H-T-H, zinc fingers, and homeodomain are DNA-binding motifs.
Question 10
Which DNA-binding motif has two short helical segments separated by a turn?
A. H-L-H
B. Leucine zipper
C. Zinc fingers
D. H-T-H
View Answer
Answer: Option D
Explanation:
The H-T-H DNA-binding motif has two short helical segments separated by a turn. Leucine zipper and Zinc fingers do not have two helical segments. H-L-H has two short helical segments but they are separated by a loop.
Question 11
Which of the following DNA-binding motif functions as transcriptional regulators, especially during eukaryotic development?
A. Zinc fingers
B. Leucine zippers
C. H-T-H motif
D. Homeodomain
View Answer
Answer: Option D
Explanation:
Homeodomain is the DNA-binding motif that functions as transcriptional regulators, especially during eukaryotic development. These domains are highly conserved and have now been identified in proteins from a wide variety of organisms.
Question 12
Which of the following interactions majorly imparts specificity to most of the protein-DNA contacts?
A. Hydrophobic interaction
B. Covalent interactions
C. Disulfide bonds
D. Hydrogen bonds
View Answer
Answer: Option D
Explanation:
Hydrogen bonds majorly imparts specificity to most of the protein-DNA contacts. The discrimination between base pairs and hydrogen bond donors and acceptor groups occur in the major groove of DNA.
Question 13
Which of the following is a feature of a lac repressor?
A. It is a dimer
B. It is a trimer
C. It is a monomer
D. It is a tetramer
View Answer
Answer: Option D
Explanation:
The lac repressor is a tetramer. In this tetramer, two dimers are tethered together. This tetrameric structure of the lac repressor is an exception, as in most of the regulatory proteins the DNA-binding domain occurs in dimers.
Question 14
Which of the following proteins have discrete DNA-binding domains?
A. Excretory proteins
B. Plasma membrane proteins
C. Catalytic proteins
D. Regulatory proteins
View Answer
Answer: Option D
Explanation:
Regulatory proteins have discrete DNA-binding domains. They regulate the expression of genes in a cell. They bind to specific DNA sequences. Excretory proteins, plasma membrane proteins, and catalytic proteins do not have discrete DNA-binding domains.