Membranes II Flashcards
How many residues are there per turn of an alpha helix?
How many A/residues is this?
- 6
1. 5
How are peptide bonds linked in alpha helices?
Peptide bond 1 is H bonded to peptide bond 4
Peptide bond 2 is H bonded to peptide bond 5
…etc
How are antiparallel beta-pleated sheets formed?
Adjacent beta-strands run in opposite direction
Every other side chain extends above or below the sheet
H bonds are perpendicular to chains
How thick is the entire lipid bilayer?
How thick is the hydrophobic region?
50 Angstroms
30A
How many amino acids are needed to span the lipid bilayer?
In an alpha helix:
1 residue = 1.5A
SO need approx 20 residues
What are porins?
Beta-barrel membrane proteins
How can you predict membrane protein structure from sequence?
Hydrophobicity analysis
- each individual amino acid has a hydrophobicity value
Look for regions of hydrophobic amino acids
-> indicative of alpha-helices
=integral membrane proteins
What doesn’t hydrophobicity analysis predict?
Beta-barrel membrane proteins
What contacts the hydrophobic lipid interior?
Hydrophobic amino acids
What are the most common membrane-spanning segments?
Alpha-helices
How are membrane proteins assembled?
Almost all proteins synthesis on ribosomes
Energetically unfavourable to move large hydrophilic portions through lipid bilayer
How do hydrophilic parts of membrane proteins get across the membrane?
Assemble in a protein conducting channel
What can transmembrane helices be surrounded by?
Lipid
Other helices - not as hydrophobic
What are the 4 main types of membrane proteins?
Transporters
Linkers
Receptors
Enzymes
What are the 2 types of membrane transport?
Carrier proteins:
transport small solutes
passive or active
Ion channels
Describe carrier proteins
Have specific solute binding sites
Switch conformation as to which side is open
Describe channel proteins
Open = continuous channel
Selective - only some ions allowed through
Gated - opening + closing is regulated
What are the 3 types of transport?
Which 2 are coupled transport?
Uniport
Symport
Antiport
Symport + antiport
What is uniport?
Transports 1 type of molecule
What is symport?
Transports 2 different molecules in the same direction
Against conc grad
What is antiport?
Transports 2 different molecules in different directions
Briefly explain how symporters are used in glucose transport
Na+ binds to symporter
= increases affinity for glucose
Give an example of a passive transporter
Facilitative glucose transporters
ie GLUT1
What is lactose permeate an example of?
A symporter
- transports lactose + protons in the same direction
How are electrically charged molecules transported?
Electrochemical gradient
= conc grad + membrane potential
For a + charge:
Large EG when MP = -ve inside
Small EG when MP = +ve inside
Medium EG when MP = 0
Give an example of an antiporter
Na-K ATPase
- pumps3 Na+ out and 2K+ in using ATP
