Week 5 Bollough Lecture 1

Question 1

What is the indication that is given from how tight proteins bind onto the membrane?
- How are they solubilised?

Answer 1

The ease with which a protein can be dissociated from a membrane indicates how intimately it is associated with the membrane.

a) Some membrane proteins can be solubilized by relatively mild means, such as extraction by a solution of high ionic strength (e.g. 1 M NaCl).
b) Other membrane proteins are bound much more tenaciously; they can be solubilized only by using a detergent or an organic solvent.

Question 2

How do we classify a protein to be either peripheral or integral?

Answer 2

Membrane proteins can be classified on the basis of this difference in dissociability.

Question 3

What are peripheral proteins?

Answer 3

Peripheral membrane proteins are bound to membranes primarily by electrostatic and hydrogen-bond interactions with the head groups of lipids. These polar interactions can be disrupted by adding salts or by changing the pH.

a) Many peripheral membrane proteins are bound to the surfaces of integral proteins, on either the cytoplasmic or the extracellular side of the membrane.
b) Others are anchored to the lipid bilayer by a covalently attached hydrophobic chain, such as a fatty acid.

Question 4

What are integral proteins?

Answer 4

Integral membrane proteins interact extensively with the hydrocarbon chains of membrane lipids, and they can be released only by agents that compete for these nonpolar interactions