Chapter 3: 3.2 Alpha Helix

Question 1

Describe:

α-helix

Answer 1

A right-handed helical structure which occurs through hydrogen bonding between atoms in the amino acid backbone

Question 2

True or False:

Side chains are not involved in helix forming bonds

Answer 2

True, but different amino acids have different propensities to form α-helix

Question 3

How are side chains arranged in an α-helix?

Answer 3

Protrude off the sides of the helix and are arranged to minimize steric clashes

Question 4

True or False:

α-helix is flexible

Answer 4

False, α-helix is stretchy not flexible

Question 5

In an α-helix:

Where do hydrogen bonds occur?

Answer 5

Occur between the N-H (donor) of one residue and the C=O (acceptor) of the 4th residue from the donor
* If N-H is residue i, then the C=O acceptor is i-4

Question 6

In an α-helix:

How many residues are there per turn (360 degrees)?

Answer 6

3.6

Question 7

In an α-helix:

1. How much rise per residue?
2. How much rise across backbone?

Answer 7

1. 0.15 nm (1.5Å)
2. 0.54 nm (5Å)

Question 8

In an α-helix:

Angle between neighbouring residues

Answer 8

100°

Question 9

In an α-helix:

What is the number of H-bonds present in an α-helix?

Answer 9

Number of residues - 4

Question 10

What determines the properties of an α-helix?

Answer 10

The types of side chains
* Determines properties and how it interacts with its environment

Question 11

True or False:

Polar side chains yield polar helices

Answer 11

True

Question 12

What type of helices do hydrophobic side chains yield?

Answer 12

Hydrophobic helices

Question 13

Helices that are amphipathic due to…

Answer 13

• Polar/hydrophilic side chains on one side
• Hydrophobic side chains on the other side

Question 14

What are formed between amphipathic helices?

Answer 14

Coiled-coil structures

Question 15

What are present at amphipathic helices interface?

Answer 15

Small residues