Question

In: Chemistry

Consider a alpha-helix "stretch" of a protein consisting of 20 amino acid residues compared to a...

Consider a alpha-helix "stretch" of a protein consisting of 20 amino acid residues compared to a Beta-strand "stretch" of a protein consisting of 20 amino acids(which of course is part of a Beta-sheet). What is the length of this alpha-helix and Beta-strand portion of the protein in angstroms?

Solutions

Expert Solution

Ans. # One turn (a repeating unit) of a-helix consists of 3.6 residues with a pitch of 5.4 A.

So,

Length of a-helix = (Pitch of helix) x Number of residues in helix

                                    = (5.4 A / 3.6 residues) x 20 residues

                                    = 30.0 A

# The repeating unit of antiparallel b-sheet consists of 3 residues with a length of 7.0A.

Length of b-sheet = (Length of repeating unit) x Number of residues in b-sheet

                                    = (7.0 A / 3 residues) x 20 residues

                                    = 46.67 A

# The repeating unit of parallel b-sheet consists of 3 residues with a length of 6.5A.

Length of b-sheet = (Length of repeating unit) x Number of residues in b-sheet

                                    = (6.5 A / 3 residues) x 20 residues

                                    = 4.33 A


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