## Core Concept
Tetracyclines are a class of broad-spectrum antibiotics that work by inhibiting protein synthesis in bacteria. They achieve this by binding to the bacterial ribosome, specifically to the 30S subunit. This binding interferes with the attachment of aminoacyl-tRNA to the ribosomal complex, which is essential for adding new amino acids to the growing peptide chain.

## Why the Correct Answer is Right
The correct mechanism of action of tetracyclines involves their binding to the 30S subunit of the bacterial ribosome. This binding prevents the aminoacyl-tRNA from docking at the A site of the ribosome, thereby inhibiting the initiation complex of peptide formation and the subsequent protein synthesis. This action is bacteriostatic, meaning it inhibits the growth and reproduction of bacteria rather than killing them outright.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because tetracyclines do not work by inhibiting cell wall synthesis; that is the mechanism of action for beta-lactam antibiotics like penicillins and cephalosporins.
- **Option B:** This option is incorrect as tetracyclines do not primarily act by disrupting cell membranes; that is more characteristic of antifungal agents like polyenes (e.g., amphotericin B) and certain antiseptics.
- **Option C:** While this option might seem plausible because it mentions ribosomal inhibition, it is not specific enough and could imply a different mechanism or site of action not related to tetracyclines.

## Clinical Pearl / High-Yield Fact
A key point to remember about tetracyclines is that they should be avoided in children under 8 years old and in pregnant women due to the risk of inhibiting bone growth and causing tooth discoloration. This is a critical consideration in clinical practice.

## Correct Answer Line
**Correct Answer: D. Inhibiting protein synthesis by binding to 30S ribosomal subunit.**