Lecture 2: Membrane Proteins Flashcards
T/F: Biological membranes contain one type of membrane protein
False; they contain many
Many transmembrane proteins have membrane spanning _______’s.
alpha-helices
Give an example of a membrane spanning a-helice protein
Glycophorin A
Where is glycophorin A found? What does it do?
It is a glycosylated surface protein of RBC’s, which prevents these cells from adhering to other cells or blood vessel walls
How many residues does an a-helix have ?
3.6 residues per turn
Which amino acids are likely to be found in a transmembrane domain?
A hydrophobicity plot will display what?
the average hydrophobicity values for the entire protein
A hydrophobicity plot cannot show us: (4 things)
- If the protein forms an oligomer
- With which membrane the protein associates (ie. the ER, Golgi, PM?)
- The topology of the protein (if N or C terminus are in the cytosol)
- This analysis is a prediction and must be experimentally tested
Selective membrane permeability is mediated by transmembrane proteins
which associate with the membrane as _______, ________, or ________ proteins
integral, peripheral, or lipid-anchored
How many amino acids with hydrophobic character are necessary to span a membrane of 3nm?
20
A hydrophobicity (also called hydrophathy) plot is a theoretical prediction of hydrophobic\_\_\_\_\_\_ within a protein. These could be transmembrane
domains
This domain can be identified by searching for hydrophobic domains, with
1. ΔG (apolor àwater) >0, and 2. that are long enough to span a
membrane
Which of these three 20 amino acid-long sequences is the most likely candidate for a transmembrane
domain?
A: ile thr lleu ile tyr phe gly val met ala gly val ile gly thr ile leu leu ile ser
B: ile thr pro ile tyr phe gly pro met ala gly val ile gly thr pro leu leu ile ser
C: ile thr glu ile tyr phe gly arg met ala gly val ile gly thr glu leu leu ile ser
(refer to actual slides for further questions)
