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

Options

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

Answer

To solve the question "Which alpha amino acid does not contain a primary amino group?", we can follow these steps:

### Step 1: Understand the Structure of Amino Acids
Amino acids are organic compounds that contain both an amino group (-NH2) and a carboxyl group (-COOH). The amino group can be classified based on the number of carbon atoms it is attached to:
- **Primary Amino Group**: The nitrogen is attached to one carbon atom.
- **Secondary Amino Group**: The nitrogen is attached to two carbon atoms.
- **Tertiary Amino Group**: The nitrogen is attached to three carbon atoms.

### Step 2: Identify the Relevant Amino Acids
We need to identify which alpha amino acids exist and analyze their structures to determine if they contain a primary amino group or not. Common alpha amino acids include:
- Glycine
- Alanine
- Proline
- Serine
- Cysteine
- Valine
- Leucine
- Isoleucine
- Phenylalanine
- Tryptophan
- Tyrosine
- Asparagine
- Glutamine
- Arginine
- Lysine
- Histidine
- Aspartic acid
- Glutamic acid

### Step 3: Analyze Proline
Among these amino acids, we focus on proline. The structure of proline is unique because it contains a five-membered ring where the amino group is part of the ring.

- The structure of proline can be represented as:
```
H
|
H2N - C - C - COOH
| |
C C
| |
H H
```

### Step 4: Determine the Type of Amino Group in Proline
In proline:
- The nitrogen atom is bonded to two carbon atoms (the carbon in the ring and the carbon that is part of the carboxyl group).
- Therefore, proline has a secondary amino group.

### Step 5: Conclusion
Since proline is the only alpha amino acid that does not contain a primary amino group (it has a secondary amino group), we conclude that the answer to the question is:

**Proline is the alpha amino acid that does not contain a primary amino group.**