Biochemistry—β-Pleated Sheet Details In β-pleated sheet structures, which statement is accurate about how neighboring strands relate?
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ANeighboring polypeptide chains lie side by side in an approximately planar sheet.
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BNeighboring residues along the same strand are hydrogen bonded to each other.
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CNeighboring chains are always connected by α-helices between them.
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DNeighboring chains are hydrogen bonded to each other through backbone groups.
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ENeighboring chains avoid hydrogen bonds due to steric clashes.
Answer
Correct Answer: Neighboring chains are hydrogen bonded to each other through backbone groups.
Explanation
Introduction / Context:β-Sheets are stabilized primarily by hydrogen bonds between backbone atoms of adjacent strands. This question distinguishes correct inter-strand bonding from incorrect ideas about intra-strand bonding and obligatory helical connectors.
Given Data / Assumptions:
- β-Sheets consist of multiple strands arranged side by side.
- Backbone C=O and N-H groups form inter-strand hydrogen bonds.
- Connections between strands (loops/turns) vary and are not always α-helices.
Concept / Approach:Identify which statement captures the defining stabilizing interaction. Inter-strand hydrogen bonding is the core principle; intra-strand adjacent residues typically do not hydrogen bond in β-conformation.
Step-by-Step Solution:
Step 1: Evaluate hydrogen bonding pattern. In β-sheets, hydrogen bonds run between neighboring strands, not between adjacent residues within the same strand.Step 2: Evaluate topology. Strands are connected by turns or loops; sometimes helices can connect distant elements, but this is not obligatory.Step 3: Select the statement that explicitly states inter-strand hydrogen bonding.Verification / Alternative check:Inspection of β-sheet cartoons and PDB structures confirms inter-strand hydrogen bonding as the stabilizing network, with variable types of connecting segments.
Why Other Options Are Wrong:
- Neighboring residues along the same strand: not the primary H-bonding pattern in β-strands.
- Connected by α-helices: not a rule; often short turns/loops connect strands.
- Avoid hydrogen bonds: opposite of reality—hydrogen bonds stabilize sheets.
- “Planar sheet” alone is descriptive but incomplete; hydrogen bonding is the key correct feature.
Common Pitfalls:Assuming all secondary elements are linked by helices; confusing inter-strand with intra-strand bonding; overlooking that sheets are pleated, not perfectly flat.
Final Answer:Neighboring chains are hydrogen bonded to each other through backbone groups.