Which of the following satements is not correct?

Options

A. Proteins are polyamides formed from amino acids
B. Except glycine, all other amino acids show optical activity
C. Natural proteins are commonly made up of L - isomer of amino acids
D. In `alpha-` amino acids, `-NH_(2) and -COOH` groups are attached to different carbon atoms

Answer

To determine which statement is not correct among the given options, we will analyze each statement one by one.

### Step 1: Analyze the first statement
**Statement 1:** "Proteins are polyamides formed from amino acids."

- **Explanation:** Proteins are indeed polymers made from amino acids, and they are linked by peptide bonds, which are a type of amide bond. Therefore, this statement is correct.

### Step 2: Analyze the second statement
**Statement 2:** "Except glycine, all other amino acids show optical activity."

- **Explanation:** Glycine is the simplest amino acid and has two hydrogen atoms attached to its alpha carbon, making it achiral (not optically active). All other amino acids have a chiral center and are optically active. Thus, this statement is also correct.

### Step 3: Analyze the third statement
**Statement 3:** "Natural proteins are commonly made up of L isomers of amino acids."

- **Explanation:** Most natural proteins are indeed composed of L-amino acids. This is a well-established fact in biochemistry. Therefore, this statement is correct.

### Step 4: Analyze the fourth statement
**Statement 4:** "In alpha amino acids, NH2 and COOH groups are attached to different carbon atoms."

- **Explanation:** In alpha amino acids, the amino group (NH2) and the carboxyl group (COOH) are both attached to the same carbon atom, known as the alpha carbon. This statement is incorrect because it states that they are attached to different carbon atoms.

### Conclusion
After analyzing all the statements, we find that the fourth statement is not correct.

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

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