Two fatty acid monomers are joined by

Options

A. Hydrogen bond
B. Peptide bond
C. Phosphodiester bond
D. Ester bond.

Answer

To answer the question "Two fatty acid monomers are joined by," we need to understand how fatty acids interact with each other and with other molecules, specifically glycerol.

### Step-by-Step Solution:

1. **Identify the Components**: The question mentions two fatty acid monomers. Fatty acids are carboxylic acids with long hydrocarbon chains.

2. **Understand the Joining Process**: Fatty acids can join with other molecules to form larger structures. In this case, they typically join with glycerol to form lipids.

3. **Recognize the Bond Types**: There are several types of bonds that can form between molecules:
- **Hydrogen Bond**: A weak bond that occurs between a hydrogen atom and an electronegative atom.
- **Peptide Bond**: A bond that links amino acids together in proteins.
- **Phosphodiester Bond**: A bond that links nucleotides in nucleic acids (DNA/RNA).
- **Ester Bond**: A bond formed when a fatty acid reacts with an alcohol (like glycerol), resulting in the release of water.

4. **Determine the Correct Bond**: When fatty acids combine with glycerol, they undergo a condensation reaction, where an ester bond is formed. This process involves the hydroxyl group of the glycerol reacting with the carboxyl group of the fatty acid, releasing water.

5. **Conclusion**: Therefore, the correct answer to the question is that two fatty acid monomers are joined by an **ester bond**.

### Final Answer:
Two fatty acid monomers are joined by an **ester bond**.