Lecture 7B

Question 1

a-Helix

Answer 1

• A right handed helix with 3.6 residues per turn
• A pitch of 5.4 A per turn
• Held together by H-bonds between C=O of one peptide bond and the N-H of another peptide bond
• H-bonds are parallel to the axis of the helix
• H-bonding is between the n carbonyl and the n+4 NH peptide bonds
• Can range from 11-53 amino acids in length
• Proline residues can’t form a-helices

Question 2

Beta Structures

Answer 2

• Two separate sections of polypeptide interact via H-bonds (chains are side by side)
• Form large number of hydrogen bonds between chains
• Average length is 8-15 amino acids long
• Anti parallel has straight H bonds
• Parallel has H-bonds that aren’t linear
• Side chains are pointing away from the strands