Secondary Structure Flashcards
What are the two major secondary structure elements in globular proteins?
The a-helix
The B-strand
(Both satisfy the backbone hydrogen bonds!)
What is the rise in Å units of the a-helix per residue.
1.5Å rise.
What is the rise in Å units of the a-helix per residue.
1.5Å rise.
How many residues are needed to have a complete turn of an alpha helix?
3.6 residues. (Every 4th side chain interacts with each other vertically!)
H-bond that makes this so strong is C=O at n and NH group at n+4
For all residues, the same main chain dihedrals are what?
Phi= -57
Psi= -47
What direction and what degree does the residue to residue rotation have, viewed along the axis?
100 degrees to the right .
What defines a discontinuous helix ? (4 things)
- An object (ie stairs)
- The helix axis
- A rotation of the object about the helix axis.
- A translation of the object parallel to the helix axis.
What defines what direction of a helix?(Left or right-handed?)
When looking at it, whatever way it’s going away and up from you.
Why are almost all helices Right-handed?
Because 18 amino acids are L-confirmation.
Right handed helix allows all R-groups to point away from helix.
Left handed helix has all R-groups in the middle.
What kind of interaction of strands is this? What’s notable?
Antiparallel Beta-strand
Notable: Two hydrogen bonds from the same amino acid on the same other amino acid.
What kind of interaction of strands is this? What’s notable?
Parallel Beta strand.
Still 2 H-Bonds from 1 amino acid, but to two different amino acids respectively.
Very rarely seen compared to Antiparallel.
In beta sheets, how do the side chains conform?
The twist of the sheet is Left-handed when viewed in the plane of the sheet perpendicular to the beta strand. Why?
This is due to the fact that when viewed along the beta strand, each strand has a right handed twist.
Parallel vs anti parallel sheets do not change this.
