Silph drugs/sulphanilamide kill bacteria by inhibting of which of the following ?

Options

A. Para-aminobenzoic acid
B. Felic acid
C. Phenylalanine
D. Methionin

Explanation

To solve the question regarding how sulfanilamide (a type of sulfa drug) kills bacteria, we need to understand the mechanism of action of this drug. Here’s a step-by-step breakdown:

### Step 1: Understand the Role of Sulfanilamide
Sulfanilamide is a type of antibiotic that acts as a competitive inhibitor. This means it competes with a substrate for binding to an enzyme.

**Hint:** Remember that competitive inhibitors resemble the substrate of the enzyme they inhibit.

### Step 2: Identify the Target Enzyme
The specific enzyme that sulfanilamide inhibits is called dihydropteroate synthetase. This enzyme is crucial for the synthesis of folic acid in bacteria.

**Hint:** Look for the enzyme that is involved in the synthesis of essential nutrients in bacteria.

### Step 3: Recognize the Substrate
Dihydropteroate synthetase uses para-aminobenzoic acid (PABA) as a substrate to synthesize folic acid. Sulfanilamide mimics PABA and thus inhibits the enzyme's activity.

**Hint:** Think about which compound is structurally similar to sulfanilamide and is used in the folic acid synthesis pathway.

### Step 4: Conclusion
Since sulfanilamide inhibits the enzyme dihydropteroate synthetase by competing with para-aminobenzoic acid, the correct answer to the question is that sulfanilamide kills bacteria by inhibiting para-aminobenzoic acid.

**Final Answer:** Para-aminobenzoic acid (PABA).

### Summary of Steps:
1. Recognize sulfanilamide as a competitive inhibitor.
2. Identify the target enzyme (dihydropteroate synthetase).
3. Understand that the substrate for this enzyme is para-aminobenzoic acid.
4. Conclude that sulfanilamide inhibits the use of PABA, leading to bacterial death.