Q. 25 - Biology

Question

Describe how transcription in prokaryotic cells can be altered by external stimulation such as excess lactose in the environment. 

Step-by-Step Solution

Answer

The lac repressor establishes a strong connection with the operator when lactose is absent, preventing RNA polymerase from activating transcription. However, when lactose is available, the lac repressor loses its ability to bind DNA. In doing so, it frees up space for RNA polymerase to begin transcription of the operon. It separates from the operator.

Step 1: Introduction

An illustration of an inducible operon is the lac operon. The third method of gene regulation in prokaryotic organisms involves inducible operons, which have proteins that bind to either activate or inhibit transcription depending on the local environment and the demands of the cell.

Step 2: The explanation for the answer

• The lac operon of E coli contains genes involved in the metabolism of lactose. It only manifests when both lactose and glucose are lacking.
• Two regulators that regulate the operons "off" and "on" states in reaction to lactose and glucose concentrations are lac repressor and catabolite activator protein (CAP).
• The lac repressor is a lactose sensor. When there is lactose the repressor's ability to prevent transcription of the operon in its normal state is lost. The lac repressor recognises lactose by means of its isomer allolactose.
• The transcription of the operon only begins when the blood glucose level is low. CAP indirectly detects glucose via the chemical "hunger signal" cAMP.