Which of the following statement are correct ?
(1) `alpha` - amino acids present in protein are `alpha` - L amino acids
2. Amino acids present `-NH_2` as well as - COOH group
3. Number of amino groups and crboxylic groups are always same in all `alpha` - amino acids
(4) Concentration of dipolar ion is maximum at isoeletric point
Select the correct answer from the codes given below

Options

A. Only 1 and 2
B. 1,2 and 3
C. 1,2 and 4
D. 1,2,3 and 4

Answer

To solve the question, we will analyze each statement regarding alpha-amino acids and their properties.

### Step-by-Step Solution:

1. **Statement 1: Alpha-amino acids present in proteins are alpha-L amino acids.**
- **Analysis:** Naturally occurring amino acids in proteins are predominantly L-amino acids. The L and D nomenclature refers to the configuration around the chiral carbon atom. Thus, this statement is correct.
- **Conclusion:** **Correct**

2. **Statement 2: Amino acids present -NH2 as well as -COOH group.**
- **Analysis:** By definition, amino acids contain both an amino group (-NH2) and a carboxylic acid group (-COOH). Therefore, this statement is also correct.
- **Conclusion:** **Correct**

3. **Statement 3: Number of amino groups and carboxylic groups are always the same in all alpha-amino acids.**
- **Analysis:** This statement is not correct. While most alpha-amino acids have one amino group and one carboxylic group, there are exceptions like aspartic acid, which has two carboxylic groups. Therefore, this statement is incorrect.
- **Conclusion:** **Incorrect**

4. **Statement 4: Concentration of dipolar ion is maximum at isoelectric point.**
- **Analysis:** At the isoelectric point (pI), the amino acid exists predominantly as a dipolar ion (zwitterion), where the positive and negative charges balance each other out. Thus, the concentration of dipolar ions is indeed maximum at the isoelectric point.
- **Conclusion:** **Correct**

### Final Answer:
The correct statements are **1, 2, and 4**.