`alpha`-helix is stabilized by H-bonds between the

Options

A. NH and CO group of side chain
B. NH and CO group of main chain
C. NH and NH group of same chain
D. NH and COOH group of all chain

Answer

To answer the question about what stabilizes the alpha-helix structure in proteins, we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding Alpha-Helix Structure**:
- The alpha-helix is a common secondary structure found in proteins. It is characterized by a right-handed helical shape.

2. **Role of Amino Acids**:
- In the alpha-helix, the amino acids are arranged in such a way that each amino acid contributes to the helical structure. Specifically, each amino acid corresponds to a 100-degree turn in the helix.

3. **Hydrogen Bond Formation**:
- The stability of the alpha-helix is primarily due to hydrogen bonds that form between specific groups in the amino acids.

4. **Identifying the Groups Involved**:
- The hydrogen bonds are formed between the carbonyl oxygen (CO) of one amino acid and the amide hydrogen (NH) of another amino acid that is four residues earlier in the sequence.

5. **General Pattern of Hydrogen Bonds**:
- This means that for every amino acid in the helix, its CO group will form a hydrogen bond with the NH group of the amino acid located four positions back in the sequence.

6. **Conclusion**:
- Therefore, the alpha-helix is stabilized by hydrogen bonds between the carbonyl oxygen (CO) and the amide hydrogen (NH) groups of the main chain of the amino acids.

### Final Answer:
The alpha-helix is stabilized by hydrogen bonds between the carbonyl oxygen (CO) and amide hydrogen (NH) groups of the main chain.

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