Discussion on Gene Regulation Questions

Q1. Which of the following is true of an Operon?

a)      An operon consists of structural genes only

b)      An operon consists of Strcutural genes and promoter regions

c)       An operon consists of promoter and I gene

d)      None

Explanation:

The correct answer is ‘b’ because an operon is a complete entity that includes promoter and structural genes. Since promoter region is important to bind RNA polymerase, it must be included in an operon to allow structural genes to express themselves.

Q2. The control of gene expression in prokaryotes mostly occurs at which level?

a)      Transcriptional level

b)      Translational level

c)       Replication level

d)      All of the above

Explanation:

The correct answer is ‘a’ because in prokaryotes, transcription and translation occurs simultaneously.  So, if there is no transcription then, no translation as well.

Q3. Control of gene expression in eukaryotes occurs at which level?

a)      Transcriptional level

b)      Translational level

c)       Processing level

d)      All of the above

Explanation:

The correct answer is ‘d’ because in eukaryotes, transcription and translation processes are separated by the nuclear membrane. In other words, transcription and post transcriptional modifications are done in the nucleus and translation occurs in the cytoplasm.

Q4. Which of the following is a constitutive gene?

a)      I gene

b)      Z gene

c)       Y gene

d)      A gene

Explanation:

The correct answer is ‘a’ because I gene is always on. It is also called as housekeeping gene. On the other hand, Z, Y, and Z genes are expressed under certain conditions like the glucose and lactose level.

Q5. In Lac Operon, when the repressor gene binds to the operator, no transcription and translation process occurs. This type of regulation is called:

a)      Positive regulation

b)      Negative regulation

c)       Neutral regulation

d)      None

Explanation:

The correct answer is ‘b’ because the repressor protein, as the name suggests represses the process of transcription and translation. So, it is called negative regulation.

Q6. What happens when the concentration of lactose in the cell increases?

a)      The repressor protein attaches to the lactose and the combined structure binds to the operator to switch off the process of transcription and translation

b)      The repressor protein binds to the operator without binding to the lactose molecules

c)       Lactose molecules inhibit the repressor protein to bind to the operator sequence

d)      The repressor protein attaches to the lactose and the combined structure fails to bind to the operator to switch on the process of transcription and translation

Explanation:

The correct answer is ‘d’ because lactose acts as an inducer. When there is no lactose in the cell, no transcription and translation process occurs. In this situation, repressor protein binds to the operator sequence to switch off the process of transcription and translation. This is because, the cell already has sufficient amount of glucose. However, when the lactose concentration increases, it means, there is low amount of sugar in the cell and lactose needs to be converted to glucose and galactose to get energy. So, lactose induces the repressor protein and the two collectively fails to bind to the operator. So, when repressor is not attached to the operator, the process of transcription and translation occurs smoothly.  

 Q7. Tryptophan in Trp Operon is called as:

a)      Repressor

b)      Co-repressor

c)       Inhibitor

d)      Suppressor

Explanation:

The correct answer is ‘b’ because when the tryptophan concentration in the cell increases due to rapid transcription and translation process, further synthesis is not required. In that situation, tryptophan attaches itself to the repressor protein and both collectively attaches to the operator sequence to switch off the process.  Since tryptophan attaches to the repressor protein to inhibit the process of transcription and translation – it is called co-repressor.