Lecture 6 - Membranes Flashcards
What do membranes do?
define boundaries and serve as permeability barriers
- membranes are needed to separate functions (i.e., proteins are not made in the nucleus)
Fluid mosaic models
membrane = a fluid bilayer of lipids
proteins (and other molecules) = mosaic
Different types of lipids in membranes
- phospholipids
- glycolipids
- sterols
What does it mean that the membrane is asymmetric?
phospholipids diffuse
What are translocates?
proteins that move phospholipids between layers and maintain the lipid symmetry
- prevent lipids from being homogenous
What are the 3 types of translocases?
- Flippase: moves lipids inside
- Floppase: moves lipids outside
- Scramblase: moves lipids in and out
What is FRAP?
Fluorescence Recovery After Photobleaching
- a method to study the mobility of molecules in living cells
- cell surface molecules (i.e., phospholipids) are labeled w/ fluorescent dye
- laser beam bleaches an area of cell surface => fluorescent molecules stop working but does not destroy membrane
- fluorescent-labeled molecules diffuse into bleached area
- bleached area disappears as lipids move laterally
Proteins at membrane must have what?
hydrophobic amino acids
What kind of proteins do membranes contain?
- integral: have a hydrophobic region
- peripheral: associate through another membrane protein
- lipid-anchored: bind fatty acids which gets inserted into the membrane
Types of integral membrane proteins
- integral monotropic protein
- singlepass protein
- multipass protein
- multi-subunit protein
Types of lipid-anchored membrane proteins
- fatty acid or isoprenyl anchor
- GPI anchor
Membrane proteins _______ and ________ electrical and chemical signals
detect; transmit
What can membrane proteins mediate?
cell adhesion and cell-cell communication
- cadherin to cadherin binding keep cells together
What are most integral proteins? What can they do?
transmembrane proteins => can move ions across cell membranes
Integral monotropic proteins
- only on one side of the membrane
- very rare
Peripheral membrane proteins
form weak and reversible associations to the membrane, typically through binding to integral membrane proteins
- do not have hydrophobic parts => cannot be in membrane
Lipid-anchored membrane proteins
covalently bound to fatty acids or isoprenyl groups
What is an example of a lipid-anchored membrane protein
trehalase - an enzyme that cuts trehalose into 2 glucose molecules
its bound to glycosylphosphatidylinositol
Proteins and lipids in the ________ of the membrane are ________
outside; glycosylated
What is glycosylation?
the process by which a carbohydrate is covalently attached to a target macromolecule
- N-linked gylcosylation of asparagine
- O-linked glycosylation of serine or threonine
