Blocking enzyme action through blocking its active sites is
(a) Allosteric inhibition
(b) Feedback inhibition
(c) Competitive inhibition
(d) Non-competitive inhibition

Options

A. Allosteric inhibition
B. Feedback inhibition
C. Competitive inhibition
D. Non-competitive inhibition.

Answer

To solve the question "Blocking enzyme action through blocking its active sites is," we need to analyze the options provided and understand the types of enzyme inhibition.

### Step-by-Step Solution:

1. **Understanding Enzyme Inhibition**: Enzyme inhibition refers to the process where the activity of an enzyme is decreased or halted. This can occur through various mechanisms, and it is crucial to identify how the inhibition occurs.

2. **Evaluating the Options**:
- **(a) Allosteric Inhibition**: This type of inhibition occurs when an inhibitor binds to a site other than the active site (the allosteric site), causing a change in the enzyme's shape and function. It does not block the active site directly.
- **(b) Feedback Inhibition**: This is a regulatory mechanism where the end product of a metabolic pathway inhibits an enzyme involved in its synthesis. It does not specifically block the active site.
- **(c) Competitive Inhibition**: In this type of inhibition, a molecule that resembles the substrate competes with the substrate for binding to the active site of the enzyme. When the inhibitor binds to the active site, it blocks the substrate from binding, thus inhibiting the enzyme's action.
- **(d) Non-competitive Inhibition**: This occurs when an inhibitor binds to an enzyme at a site other than the active site, which alters the enzyme's function regardless of whether the substrate is bound. It does not block the active site directly.

3. **Identifying the Correct Answer**: Since the question specifically asks about blocking the active site of the enzyme, the correct answer is **(c) Competitive inhibition**. In competitive inhibition, the inhibitor directly competes with the substrate for the active site, effectively blocking it.

### Final Answer:
(c) Competitive inhibition