Alpha helices

Question 1

How is there great stability in the helical structure

Answer 1

Amid H of each peptide linkage forms hydrogen bonds with the carbonyl O of the peptide bond 4 residues away

Question 2

Where do the side chains of amino acids project

Answer 2

Project outwards from the helical polypeptide backbone

Question 3

What can stabilise or destablise the helical structure

Answer 3

interactions between the side chains

Question 4

What resides with the same charge cannot form an alpha helix at pH 7 and wy

Answer 4

Glu residues negatively charged.
Lys and Arg residues positively charged.
Like charges will repel each other at pH 7

Question 5

What residues can destablise an alpha helix due to their bulk and shape

Answer 5

Asn Asparganine,
Ser Serine,
Thr Threonine,
Cys Cysteine,

Question 6

Critical interactions occur between an amino acid side chain and a side chain how many residues away?

Answer 6

3 or 4

Question 7

Positively charged residues are usually found 1)how many residues away 2) from what type of residue 3) allows the formation of

Answer 7

1) 3
2) Negatively charged
3) Formation of ion pairs

Question 8

Aromatic residues are similarly spaced as what and what does this result in

Answer 8

similarly spaced as the positively and negatively charged side chains so 3/4 residues away.
results in hydrophobic interactions

Question 9

Which amino acids are incapable of forming alpha helices and why? (two of them)

Answer 9

Proline - Nitrogen atom part of a rigid ring and rotation about the bond is not possible which produces a kink and destablises helix
Glycine - Has more conformational flexibility than other residues and tends to take up coiled structures different to alpha

Question 10

How is there a small electric dipole in alpha helices

Answer 10

The partial + and - charges of the helix reside mainly at the amino and carbonyl ends.
These ends attract the opposite charged amino acids which is stabilising. However there will be same charged residues too which would be destabilising.

Question 11

The 5 summaries of alpha helix

Answer 11

1) Electrostatic repulsion between successive charged
2) Bulkiness of adjacent R groups
3) Interactions between R groups spaced 3 or 4 resides apart
4) Occurence of proline and glycine residues
5) Interaction between amino acid residues at the end of a helical segment due to the inherent electric dipole to the alpha helix