Week 7 Part 2: Membrane Structure (Proteins) Flashcards
Section 2: Week 1
What are the three types of integral (inserted) membrane proteins?
Transmembrane, monolayer associated, and lipid-linked
How many times does a transmembrane cross the entire membrane?
At LEAST once
What is the name the one type of peripheral membrane protein?
Protein-attached
Membrane proteins have __________ _________
specific functions
What does it mean when it is said that “extraction methods (of membrane proteins) use detergents”?
It means extraction methods of integral membrane proteins destroy the lipid bilayer (because it’s integrated into it)
How are peripheral membrane proteins bound to lipids or other proteins?
By non-covalent interactions
What does it mean when it is said “gentle extraction methods (of peripheral membrane proteins) used”?
It means that the methods used to extract peripheral membrane proteins keep the lipid bilayer intact
Transmembrane proteins are ___________
amphipathic
Describe the different domains of transmembrane proteins
Hydrophilic domains: aqueous; AA side chains are polar
Hydrophobic domains: membrane-spanning; AA side chains are non-polar
What are the three examples of membrane spanning domains? Describe them.
- Single alpha-helix: a single alpha helix with hydrophobic side chains wedged between lipids
- Multiple alpha-helices: hydrophilic side chains form an aqueous pore while hydrophobic side chains interact with phospholipid tails
- Beta-barrel: Rigid channel, doesn’t undergo conformational changes
Approximately how long is a membrane spanning alpha helix?
Apprx. 20-30 hydrophobic amino acids
True or false: Specific orientation for membrane proteins matter
True - it is important especially for functions
What are examples of membrane protein functions? Give an example of a membrane protein with that function.
Transporters and Channels: Na+-K+ pump, K+ leak channel (multiple a-helices)
Anchors: Integrins (single a-helix)
Receptors: Receptor kinases (PDGF-R) (single a-helix)
Enzymes: Adenylyl cyclase (multiple a-helices)
What techniques are used to identify specific types of membrane protein structures?
- X-ray Crystallography: determines 3D structure
- Hydrophobicity plots: Segments of 20-30 hydrophobic amino acids can span the lipid bilayer as an a-helix (Easy to spot the hydrophobic alpha helices)
How do you interpret hydrophobicity plot graphs? (what does the x and y axis represent?)
Y axis: Hydropathy index; the more positive (+delta G) the more hydrophobic, the more negative (-delta G) the more hydrophilic
X axis: amino acid number
Why are proteins on cytosolic face anchored by an ampiphatic a-helix?
One side is facing the hydrophobic lipid tails, the other is facing the cytosol and therefore has to be hydrophilic
Describe lipid-linked membrane proteins that have a GPI (glycosylphosphatidylinositol) anchor
- synthesis in ER lumen
- end up on cell surface (noncytosolic face)
Describe lipid-linked membrane proteins that have a lipid anchor (fatty acid, prenyl)
- cytosolic enzymes add anchor
- directs protein to cytosolic face
What is lateral diffusion of membrane proteins?
Lateral diffusion within leaflet - no flip-flop
What does FRAP stand for and what is it the study of/what are we trying to find out?
FRAP: Fluourescene Recovery After Photobleaching. It is the study of protien movement, we want to find out which proteins move around and which don’t.
What are proteins fused to in FRAP?
GFP - Green Fluorescent Protein
True or False: Lateral mobility of proteins can be restricted
True (and their are different techniques to do this)
Describe the process of FRAP
- Protein fused to GFP or labelled with fluorescent antibody
- Photobleach an area (it turns white)
- Recovery: neighbouring unbleached fluorescent proteins randomly move around, migrate in (you measure how fast it becomes green again)
What is the Rate of Fluourescence Recovery? How do you read graphs in relation to FRAP?
The Rate of Fluorescence Recovery is the time taken for neighbouring unbleached fluourescent proteins to move into bleached areas. You can see this on graphs depending on how steep the recovery curve is – the steeper the curve, the faster (and most likely greater) recovery, the flatter the curve, the slower (and more likey less) the recovery
