Which of the following amino acids possesses a non-polar side chain ?

Options

A. isoleucine
B. serine
C. cysteine
D. glutamic acid

Answer

To determine which amino acid possesses a non-polar side chain, we will analyze the structures of the given amino acids one by one.

### Step 1: Understand the General Structure of Amino Acids
The general structure of an amino acid is represented as:
\[ \text{NH}_2 - \text{CHR} - \text{COOH} \]
Where:
- NH2 is the amino group
- COOH is the carboxyl group
- R is the side chain that varies among different amino acids.

### Step 2: Analyze the Side Chains of Each Amino Acid

1. **Isoleucine (Ile)**
- Structure: The side chain of isoleucine is represented as:
\[ \text{CH}_2 - \text{CH(CH}_3)_2 \]
- This side chain consists of only carbon (C) and hydrogen (H) atoms. The bonds formed between carbon and hydrogen are non-polar due to the negligible difference in electronegativity.
- Conclusion: Isoleucine has a non-polar side chain.

2. **Serine (Ser)**
- Structure: The side chain of serine is:
\[ \text{CH}_2 - \text{OH} \]
- The presence of the hydroxyl (OH) group indicates that there is a polar bond due to the significant electronegativity difference between oxygen and hydrogen.
- Conclusion: Serine has a polar side chain.

3. **Cysteine (Cys)**
- Structure: The side chain of cysteine is:
\[ \text{CH}_2 - \text{SH} \]
- The presence of the sulfhydryl (SH) group indicates a polar bond, as sulfur is more electronegative than hydrogen.
- Conclusion: Cysteine has a polar side chain.

4. **Glutamic Acid (Glu)**
- Structure: The side chain of glutamic acid is:
\[ \text{CH}_2 - \text{CH}_2 - \text{COOH} \]
- The presence of another carboxyl group (COOH) indicates that this side chain is also polar, as it can release a proton (H+) and has a significant electronegativity difference.
- Conclusion: Glutamic acid has a polar side chain.

### Step 3: Final Conclusion
After analyzing all the amino acids:
- Isoleucine is the only amino acid with a non-polar side chain.

### Answer
The amino acid that possesses a non-polar side chain is **Isoleucine**.

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