Multiple Choice
In the context of protein secondary structure, is the alpha helix typically a right-handed or left-handed coil?
4. Protein Structure
Alpha Helix
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In an \( \alpha \)-helix, which type of interaction primarily stabilizes the helical structure?
A
Hydrogen bonds between the carbonyl oxygen of residue \( i \) and the amide hydrogen of residue \( i+4 \)
B
Hydrophobic interactions among nonpolar side chains
C
Ionic interactions between side chains
D
Disulfide bonds between cysteine residues
Verified step by step guidance1
Understand the structure of an α-helix: The α-helix is a common secondary structure in proteins, characterized by a coiled shape stabilized by specific interactions.
Identify the primary stabilizing interaction: The α-helix is stabilized by hydrogen bonds formed between the carbonyl oxygen of one amino acid (residue i) and the amide hydrogen of another amino acid located four residues away (residue i+4). This pattern of hydrogen bonding is crucial for maintaining the helical structure.
Evaluate the other options: Hydrophobic interactions among nonpolar side chains contribute to protein folding but are not the primary stabilizing force in an α-helix. Similarly, ionic interactions between side chains and disulfide bonds between cysteine residues are important for tertiary and quaternary structures, not secondary structures like the α-helix.
Relate the hydrogen bonding pattern to the α-helix geometry: The hydrogen bonds align parallel to the axis of the helix, ensuring the stability and regularity of the structure. This arrangement allows the α-helix to maintain its characteristic shape.
Conclude that hydrogen bonds between the carbonyl oxygen of residue i and the amide hydrogen of residue i+4 are the primary stabilizing interaction in an α-helix, distinguishing it from other types of protein structures.
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