Which of the following amino acids have side chain that are negatively charged under physiogical conditions ?

Options

A. Aspartic acid
B. Histidine
C. Tryosine
D. Serine

Answer

To determine which amino acids have side chains that are negatively charged under physiological conditions (pH 7), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of Amino Acids**:
- Amino acids consist of a central carbon atom (alpha carbon) bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a unique side chain (R-group).

2. **Identify the Charge of Side Chains**:
- The charge of the side chain (R-group) of an amino acid can vary depending on the pH of the environment. At physiological pH (around 7), some side chains can be negatively charged.

3. **List the Standard Amino Acids**:
- There are 20 standard amino acids. Among these, we need to identify which ones have negatively charged side chains at pH 7.

4. **Identify Amino Acids with Negatively Charged Side Chains**:
- The two amino acids that have negatively charged side chains at physiological pH are:
- **Aspartic Acid (Asp, D)**: The side chain contains a carboxyl group (-COOH) that can lose a proton (H+) and become negatively charged (-COO^-).
- **Glutamic Acid (Glu, E)**: Similar to aspartic acid, glutamic acid has a longer side chain that also contains a carboxyl group which can lose a proton and become negatively charged.

5. **Conclusion**:
- Therefore, the amino acids with negatively charged side chains under physiological conditions are **Aspartic Acid** and **Glutamic Acid**.

### Final Answer:
The amino acids that have side chains that are negatively charged under physiological conditions are **Aspartic Acid** and **Glutamic Acid**.

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