`alpha`amino acids are those which

Options

A. participates in protein synthesis
B. COOH group and `NH_(2)` group are attached on same carbon
C. 20 types
D. all the above are correct

Answer

### Step-by-Step Solution:

1. **Definition of Alpha Amino Acids**:
- Alpha amino acids are defined as amino acids in which both the carboxylic group (-COOH) and the amino group (-NH2) are attached to the same carbon atom, which is known as the alpha carbon.

2. **Structure of Alpha Amino Acids**:
- The general structure of an alpha amino acid can be represented as follows:
- The alpha carbon is bonded to:
- An amino group (-NH2)
- A carboxylic group (-COOH)
- A hydrogen atom
- An R group (alkyl group or side chain that varies among different amino acids)

3. **Participation in Protein Synthesis**:
- Alpha amino acids are the building blocks of proteins. They participate in protein synthesis by linking together through peptide bonds to form polypeptides and proteins.

4. **Types of Alpha Amino Acids**:
- There are 20 standard alpha amino acids that are commonly found in proteins. These amino acids vary based on the R group attached to the alpha carbon, leading to different properties and functions.

5. **Conclusion**:
- Based on the definitions and characteristics discussed, we can conclude that:
- Alpha amino acids participate in protein synthesis.
- They have the carboxylic group and amino group attached to the same carbon.
- There are 20 different types of alpha amino acids.
- Therefore, the correct answer to the question is "all of the above are correct."