Week 5 Bollough Lecture 5

Question 1

Porins are only found in outer membranes. Why are they not suitable as channel proteins for inner membranes or most eukaryotic membranes?

Answer 1

because porin are wide therefore leaky

Question 2

Why is hydrogen bonding important in the architecture of porins?

Answer 2

To keep the channel stable and open at all times through the long membrane

Question 3

What are alpha helical membrane proteins?

Answer 3

Proteins that can span the membrane with alpha helices

Question 4

What is a bacteriorhodopsin?

Answer 4

An alpha helical membrane protein

a) An archaeal protein
b) Uses light energy to transport protons from inside to outside the cell, generating a proton gradient used to form ATP.
c) Bacteriorhodopsin (bR) is built almost entirely of seven closely packed α helices, nearly perpendicular to the plane of the cell membrane
d) They span its 45-Å width.

Question 5

What is the structure of a bacteriorhodopsin?

Answer 5

The primary structure reveals that most of the amino acids in these membrane- spanning α helices are non-polar and only a very few are charged. Charged amino acid inside mean they have an important role in the protein

a) This distribution of nonpolar amino acids is sensible because these residues are either in contact with the hydrocarbon core of the membrane or with one another.
b) Membrane-spanning helices are the most common structural motif in membrane proteins.