Question

Why do common folding patterns appear in proteins that exhibit very different primary structures?

The carbonyl and amino groups of the amino-acid residues at the N- and C-termini of proteins form regular patterns of hydrogen bonds that define α-helix and β-sheet shapes.

The carbonyl and amide groups of the polypeptide backbone form regular patterns of hydrogen bonds that define α-helix and β-sheet shapes.

The carbonyl and amino groups of glutamate and glutamine, respectively, form regular patterns of ionic bonds that define α-helix and β-sheet shapes.

The carboxyl and amino groups of the amino-acid residues at the N-and C-termini of proteins form regular patterns of ionic bonds that define α-helix and β-sheet shapes.

The carbonyl and amide groups of the amino-acid sidechains form regular patterns of hydrogen bonds that define α-helix and β-sheet shapes.

Answer 1

The second option is the correct answer, i.e. The carbonyl and amide groups of the polypeptide backbone form regular patterns of hydrogen bonds that define α-helix and β-sheet shapes.

Reason : This option is obviously correct because the other options are completely wrong. The hydrogen bonding is ALWAYS formed by the polypeptide backbone only, and not by individual amino acid residues or their side chains. Moreover, ionic bonds are not involved in alpha helix and beta sheets. So only 2nd option satisfies this criteria. Ionic bonds or Hydrogen bonding by side chains or individual amino acid residues aren't involved in such secondary structures. The hydrogen from amide group forms hydrogen bonding with oxygen from carbonyl group in a defined pattern. These patterns determine the respective shapes of secondary and tertiary structure.

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