Which alpha `alpha- ` acid does not contain primary amino group ?

Options

A. Proline
B. Threonine
C. Lysine
D. All of these

Answer

To determine which alpha amino acid does not contain a primary amino group, we need to analyze the structures of the given amino acids.

### Step-by-Step Solution:

1. **Understanding Primary Amino Group**:
- A primary amino group (–NH2) is one where the nitrogen atom is bonded to one carbon atom and has two hydrogen atoms attached to it.

2. **Identifying the Amino Acids**:
- The amino acids we will analyze are Proline, Threonine, and Lysine.

3. **Analyzing Proline**:
- The structure of Proline is:
```
NH
|
CH2
|
CH2
|
COOH
```
- In Proline, the nitrogen is bonded to two carbon atoms (the carbon in the ring structure) and has only one hydrogen atom. Therefore, Proline has a secondary amino group, not a primary one.

4. **Analyzing Threonine**:
- The structure of Threonine is:
```
CH3
|
CH
|
OH
|
NH2
|
COOH
```
- In Threonine, the nitrogen is bonded to one carbon atom and has two hydrogen atoms attached. Thus, Threonine contains a primary amino group.

5. **Analyzing Lysine**:
- The structure of Lysine is:
```
NH2
|
CH2
|
CH2
|
CH2
|
COOH
```
- In Lysine, the nitrogen is also bonded to one carbon atom and has two hydrogen atoms. Therefore, Lysine also contains a primary amino group.

6. **Conclusion**:
- Among the amino acids analyzed, Proline is the only one that does not contain a primary amino group. It has a secondary amino group instead.

### Final Answer:
**Proline** does not contain a primary amino group.