L11 Membrane Proteins Flashcards
Membrane proteins participate in many important biological processes. What are they? (5)
- Ion pumps and channels (regulate ionic balance of the cell)
- Carriers of larger molecules across the membrane
- Cell surface receptors
- Conveyors of cell identity
- Converters of energy stimuli
Why is the membrane called the fluid mosaic model?
Fluid: Phospholipids can move laterally within the plane of the membrane, making it flexible and dynamic
Mosaic: Contains a variety of proteins embedded within it, like a mosaic of different tiles
How can the rapid lateral movement of proteins be visualised?
A technique called fluorescence recovery after photobleaching (FRAP)
(Attach a fluorescent reagent that binds to membrane lipid. Laser light bleaches (no fluorescent) bound reagent which reduces the fluorescence in the area so forms a dark patch. Bleached area regains fluorescence as molecules diffuse in and out
Are biological membrane symmetrical or asymmetrical?
They are asymmetrical because each side have different protein components and different enzymatic activities like a Na+/K+ pump
Membrane proteins are classified into 3 types. What are they?
Integral membrane proteins (intrinsic)
Peripheral or membrane - associated proteins (extrinsic)
Lipid - anchored membrane proteins
Which membrane protein tends to be transmembrane?
Integral membrane proteins (intrinsic)
Which part of the membrane do the residues of intrinsic proteins interact with?
Residues interact with hydrophobic membrane interior
What types of residues do transmembrane helices have a high percentage of?
Hydrophobic residues
How does transmembrane proteins span across the membrane?
They often use alpha helices
But can also use special beta sheet arrangements
How does a beta barrel form?
Beta sheets consisting of between 8 and 22 beta sheets can wrap around to form these structures
These proteins typically form pores or receptors
Where are beta barrels often found?
They are often found in bacteria and in the outer membranes of mitochondria and chloroplasts
Are all integral membranes transmembrane?
No. Integral membrane proteins do not have to cross the membrane.
They do require detergent to release them from the membrane
What are lipid-anchored membrane proteins?
These lipid molecules, such as fatty acids or lipid groups, anchor the proteins to the lipid bilayer of the membrane
What are the two main classes of membrane transfer proteins?
Channels/pores - central passage for ions or molecules. Diffusion both ways depending on concentration gradient
Transporters - Specifically bind solutes
