Biochemistry Questions and Answers – Regulation of Gene Expression in Prokaryotes – 2

This set of Biochemistry online quiz focuses on “Regulation of Gene Expression in Prokaryotes – 2”.

1. CAP is ____________
a) Catabolite gene activator protein
b) Catabolite gene repressor protein
c) Anabolite gene activator protein
d) Anabolite gene repressor protein
View Answer

Answer: a
Explanation: cAMP receptor protein or CRP is sometimes called CAP, catabolite gene activator protein.

2. Trp repressor is a ____________
a) Homodimer
b) Homotrimer
c) Heterodimer
d) Heterotrimer
View Answer

Answer: a
Explanation: Trp repressor is formed by two identical molecules, each subunit containing 107 amino acid residues.

3. Attenuator sequences base-pair to form a stem-and-loop structure rich in ____________
a) A = T
b) G ≡ C
c) A = C
d) G = C
View Answer

Answer: b
Explanation: Attenuator sequences base-pair to form a G≡C rich stem-and-loop structure closely followed by a series of U residues.
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4. Which of the following regulatory sequence allows transcription to continue?
a) Sequence 1
b) Sequence 2
c) Sequence 3
d) Sequence 4
View Answer

Answer: b
Explanation: Regulatory sequence 1 is crucial for a tryptophan sensitive mechanism.
Sequence 2 is an alternative complement for sequence 3.
Sequence 4 is for attenuating transcription.

5. Formation of the attenuator stem-and-loop structure depends on the events that occur during translation of ____________
a) Regulatory sequence 1
b) Regulatory sequence 2
c) Regulatory sequence 3
d) Regulatory sequence 4
View Answer

Answer: a
Explanation: Formation of the attenuator stem-and-loop structure depends on the events that occur during translation of regulatory sequence 1, which encodes a leader peptide.
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6. Which of the following takes place when tryptophan levels are low?
a) Ribosomes quickly translates sequence 1
b) Sequence 2 is blocked before sequence 3 is transcribed
c) Ribosomes pauses at the Try codons in sequence 1
d) Attenuation at the attenuator structure formed by sequences of 3 and 4
View Answer

Answer: c
Explanation: a, b and d take place when tryptophan levels are high.

7. Which of the following takes place when tryptophan levels are high?
a) Attenuation at the attenuator structure formed by sequences of 3 and 4
b) Ribosomes pauses at the Try codons in sequence 1
c) Formation of paired structure between 2 and 3 sequences prevents attenuation
d) 2:3 structures, unlike the 3:4 attenuator, does not prevent transcription
View Answer

Answer: a
Explanation: b, c and d take place when tryptophan levels are low.
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8. Whose interaction with Lex-A facilitates the repressor’s self-cleavage reaction?
a) Rec-A
b) Rec-B
c) Rec-C
d) Rec-D
View Answer

Answer: a
Explanation: This type of function of Rec-A is called co-protease activity.

9. When DNA segment is in one orientation ____________
a) The gene for FljB and gene encoding FljA are expressed
b) The gene for FliC are expressed
c) The gene for FljB and gene encoding FljA are not expressed
d) The gene for FljB and gene encoding FljC are not expressed
View Answer

Answer: a
Explanation: When DNA segment is in one orientation, the gene for FljB and gene encoding FljA are expressed; the repressor shuts down expression of the gene for FliC.
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10. Which of the following encodes recombinase?
a) fliC
b) fljB
c) hin
d) fljA
View Answer

Answer: c
Explanation: The hin gene encodes the recombinase that catalyzes the inversion of the DNA segment containing fljB promoter and the hin gene.

Sanfoundry Global Education & Learning Series – Biochemistry.

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