## **Core Concept**
Sulphonamides are a class of antimicrobials that work by inhibiting folic acid synthesis in bacteria. Para-Aminobenzoic Acid (PABA) is a key component in the bacterial synthesis of folic acid.

## **Why the Correct Answer is Right**
Sulphonamides structurally resemble PABA and competitively inhibit the enzyme **dihydropteroate synthase**. This enzyme is crucial for the conversion of PABA into dihydropteroic acid, a precursor in folic acid synthesis. By competing with PABA, sulphonamides effectively reduce the synthesis of folic acid in bacteria, which is essential for their growth and proliferation.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option does not accurately describe the relationship between sulphonamide and PABA.
- **Option B:** This option is incorrect because it does not specify the correct relationship.
- **Option D:** This option is incorrect as it suggests a different mechanism or relationship that is not accurate.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that sulphonamides are bacteriostatic, meaning they inhibit bacterial growth rather than killing bacteria outright. They are often used in combination with other drugs, like trimethoprim, which inhibits a later step in folic acid synthesis, to achieve a synergistic bactericidal effect.

## **Correct Answer:** . Competitive inhibition.