​The hemagglutinin protein in influenza virus contains a long α-helix, with 53 residues. Which of the following correctly describes the attributes of this α-helix?​

Correct option is A

Explanation-

1. Length of the α-helix:
Standard rise per residue in an α-helix = 1.43 Å (some sources say ~1.5 Å, but 1.43 is more accurate for biological α-helices).

$$\text{Length} = 53 \, \text{residues} \times 1.43\, \text{\AA} = 75.79\, \text{\AA}$$   (Very close to 75.6 Å)

2. Number of Turns:
Standard residues per turn in an α-helix = 3.6 residues/turn.​​

$$\text{Number of turns} = \frac{53}{3.6} \approx 14.72$$

Which rounds to 14 turns (as full turns).

3. Number of Hydrogen Bonds:
Hydrogen bonding in α-helices follows this rule:
A hydrogen bond forms between the C=O of residue i and the N-H of residue i+4.

Hence, the number of hydrogen bonds is:     

                                                 $$\text{H-bonds} = \text{Total residues} - 4 = 53 - 4 = 49$$

​However, in practice and for longer helices, stabilizing hydrogen bonds may be estimated differently (e.g., some regions can form more overlapping bonds). A commonly used rough estimate in structural biology:
                                                 Average H-bonds per turn ≈7.2–7.3

                                                   So, H-bonds≈14×7.3=102.2

Hence, 102 hydrogen bonds is a reasonable and correct estimate for this 53-residue α-helix.

So, the correct answer is option a - The length is 75.6 Å, 14 turns, total of 102 Hydrogen bonds