In a protein, amino acids are linked by

Options

A. Peptide bonds
B. Glycosidic bonds
C. Hydrogen bonds
D. All the above.

Answer

To solve the question "In a protein, amino acids are linked by," we can follow these steps:

### Step-by-step Solution:

1. **Understanding Amino Acids**:
- Amino acids are the building blocks of proteins. They are organic compounds that contain both an amino group (-NH2) and a carboxyl group (-COOH).

2. **Identifying Types of Bonds**:
- In the context of proteins, there are several types of bonds that can be formed:
- **Peptide Bonds**: These are the specific bonds that link amino acids together to form proteins.
- **Glycosidic Bonds**: These bonds link sugars together, not amino acids.
- **Hydrogen Bonds**: These are weak bonds that can occur between different parts of a protein or between proteins, but they do not link amino acids directly.

3. **Formation of Peptide Bonds**:
- A peptide bond is formed when the carboxyl group of one amino acid reacts with the amino group of another amino acid, releasing a molecule of water (a dehydration synthesis reaction). This bond is crucial for forming the primary structure of proteins.

4. **Conclusion**:
- Since the question asks specifically how amino acids are linked in a protein, the correct answer is **peptide bond**.

### Final Answer:
In a protein, amino acids are linked by **peptide bonds**.

---