Regulation of lac operon by repressor is called

Options

A. Negative regulation
B. Positive regulation
C. Neutral regulation
D. Both (2) and (3)

Answer

### Step-by-Step Solution:

1. **Understanding the Lac Operon**: The lac operon is a set of genes responsible for the metabolism of lactose in bacteria, particularly E. coli. It consists of structural genes that code for enzymes needed to break down lactose.

2. **Role of the Repressor**: In the absence of lactose, a repressor protein binds to the operator region of the lac operon, preventing transcription of the structural genes. This means that the genes responsible for lactose metabolism are not expressed when lactose is not available.

3. **Definition of Negative Regulation**: The process by which the lac operon is inhibited by the repressor is referred to as negative regulation. This is because the presence of the repressor prevents gene expression, effectively "turning off" the operon.

4. **Presence of Lactose**: When lactose is present in the environment, it binds to the repressor, causing a conformational change that releases the repressor from the operator. This allows transcription of the structural genes to occur, leading to the production of enzymes that metabolize lactose.

5. **Conclusion**: Therefore, the regulation of the lac operon by the repressor is called negative regulation, as it involves the inhibition of gene expression in the absence of lactose.