Which of the following statement is not correct ?

Options

A. proteins are polymides formed from amino acids
B. except glycine, all other amino acids show optical activity
C. nature proteins are made up of L - isomers of amino acids
D. in `alpha` amino acids, `-NH_(2)` and `-COOH` groups are attached to different carbon atoms

Answer

To solve the question, "Which of the following statements is not correct?" we will analyze each statement provided in the options.

### Step-by-Step Solution:

1. **Statement 1: Proteins are polyamides formed from amino acids.**
- **Analysis:** This statement is correct. Proteins are indeed polymers (polyamides) that are formed by the linkage of amino acids through peptide bonds.

2. **Statement 2: Except glycine, other amino acids show optical activity.**
- **Analysis:** This statement is also correct. Glycine is the only amino acid that is not optically active because it does not have a chiral center. All other amino acids (except glycine) have at least one chiral carbon and thus can show optical activity.

3. **Statement 3: Naturally occurring proteins are made up of L isomers of amino acids.**
- **Analysis:** This statement is correct. Naturally occurring proteins are composed predominantly of L-amino acids, which are the enantiomers of amino acids that are biologically active in proteins.

4. **Statement 4: In alpha amino acids, NH2 and COOH groups are attached to different carbon atoms.**
- **Analysis:** This statement is incorrect. In alpha amino acids, the amino group (NH2) and the carboxyl group (COOH) are attached to the same carbon atom, which is known as the alpha carbon.

### Conclusion:
The statement that is not correct is **Statement 4**: "In alpha amino acids, NH2 and COOH groups are attached to different carbon atoms."