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 solve the question "Which of the following statements is not correct?", we will analyze each statement related to proteins and amino acids step by step.

### Step 1: Analyze the First Statement
**Statement:** "Proteins are the polyamides formed from amino acids."
**Analysis:** This statement is true. Proteins are indeed polymers (or polyamides) made up of amino acids linked by peptide bonds.

### Step 2: Analyze the Second Statement
**Statement:** "Except glycine, all other amino acids show optical activity."
**Analysis:** This statement is also true. Glycine is the only amino acid that does not have a chiral center because its R group is a hydrogen atom. All other amino acids have at least one chiral center and thus exhibit optical activity.

### Step 3: Analyze the Third Statement
**Statement:** "Natural proteins are commonly made up of L isomer of amino acids."
**Analysis:** This statement is true. Natural proteins are composed of L-amino acids (levo isomers), which are the form predominantly found in living organisms.

### Step 4: Analyze the Fourth Statement
**Statement:** "In alpha amino acid NH2 and carboxylic acid group are attached to different carbon atoms."
**Analysis:** This statement is false. In alpha amino acids, the amino group (NH2) and the carboxylic acid group (COOH) are attached to the same carbon atom, which is known as the alpha carbon.

### Conclusion
After analyzing all four statements, we find that the fourth statement is incorrect. Therefore, the answer to the question "Which of the following statements is not correct?" is the fourth statement.

### Final Answer
The fourth statement is not correct.

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