Question

2. The inducer of the lactose operon in E. coli is

1. CAP.
2. cAMP.
3. allolactose.
4. glucose.
5. galactos

3. Codons refer to triplet base sequences in the

1. mRNA.
2. nontemplate strand of DNA.
3. template strand of DNA.
4. tRNA.
5. rRNA.

Answer 1

Ans) The correct answer is "C" i.e allolactose

(Allolactose acts as an inducer of the lac operon. It binds to the repressor and reduces its affinity to bind to the operator region. Since the lac repressor cannot bind to the operator, the RNA polymerase can now easily access and bind to the promoter region to start the transcription of Lac z,y,a genes to turn ON the lac operon.

cAMP-CAP complex and lactose both are required for the lac operon to be turned ON but cAMP-CAP complex do not act as an inducer.

When both lactose and glucose is added into the medium, the lac operon is turned OFF because glucose will inhibit the synthesis of enzymes required for the lactose metabolism.This is known as glucose effect.When the glucose is depleted from the medium, synthesis of lactose metabolism enzymes starts and the lac operon will be turned ON.

Ans) The correct answer is "A" i.e mRNA

(Codon refers to the nucleotide triplet present in mRNA which is read or decoded by the ribosome by bringing appropriate tRNA having anticodons which are complementarily to the codons in the A and P site of the ribosome).