Lecture 10 Membranes Flashcards
lipid bilayer
Th e membrane is made of proteins (50%) and lipids (50%)
Lipids are amphiphilic i.e. they have
-a polar part (hydrophylic head) and
-a non-polar part (hydrophobic tail, 14-24 carbons, saturated or unsaturated, depending on the fatty acid)
phospholipids
Most lipids in the membrane are phospholipids:
- phosphoglycerides (based on glycerol)
- sphingolipids (based on sphingosine)
Most lipids have no net charge. Phospatidylserine has a net negative charge
cholesterol
Eukaryal membranes contain large amounts of cholesterol (sterol) which modulates the permeability and the packing of the membrane. By decreasing the mobility of the first few –CH 2 groups it structures the bilayer locally and makes is less prone to deformation.
-> stiffer, thicker membrane
unsaturated/saturated fatty acid
unsaturated: - hydrocarbon chain with cis-double bounds - eg oil saturated: - hydracarbon chain - eg butter
Water molecules arrange in ordered … structures around … molecules
cage-like
hydrophobic
micelle
p
liposomes
Entropy drives minimizing the number of water molecules in ordered cage-like structures, meaning that the exposed hydrophobic surfaces get minimized
Molecular motions in the lipid bilayer
lateral diffusion
rotation
flexion
flip-flop (rarely occurs)
asymmetrical membrane
p
proteins in membranes
Biological membranes contain various proteins, that can be associated to the membrane in these different ways (7)
Disulfide bonds are normally not found in the reducing environment of the …
Same goes for glycosylated proteins
cytosol
FRAP
Fluorescence recovery after photobleaching
FRAP: measuring the speed of lateral diffusion of a given protein (protein tagged with GFP)
limitation of lateral diffusion
When needed, cells can limit the lateral diffusion of membrane components
proteins stick together -> islands of proteins block the motion
Proteins can “bend” membranes, how?
- by inserting hydrophobic domains
- by binding a curved protein surface to the lipid head groups
- By specifically binding larger lipid head groups
How to get molecules across the membrane?
transporters and channels easy -> hardest: 1. hydrophobic molecules 2. small uncharged polar molecules 3. large uncharged polar molecules 4. ions
passive/active transport
passive:
- simple diffusion
- channel-mediated
- transporter-mediated
active:
- coupled transporter
- ATP-driven pump
- light driven pump
ATP-driven active transport (pumps): 3 classes
P-type: ion pump that undergoes phosphorylation
ABC-type: transport small molecules not ions
F-type/V-type: ATP-synthases, made of several different subunits, found in bacteria, mitochondria and chloroplasts, use the gradient of protons to synthesize ATP. Can also work in reverse and hydrolyze ATP in order to pump protons (V-type).
Gram+ (G+) and Gram- (G-) bacteria
G +: cell membrane and a thick peptidoglycan
G-: cell membrane, thin peptidoglycan and outer membrane with porins
Compartments of the Eukaryal cell are made of membranes
eg ER, Golgi apparatis, mithocondria
protein trafficking
Gated transport
Transmembrane transport
Vesicular transport
How proteins end up in the right place?
Signal sequences (like cinema tickets)
How do proteins get into the ER?
ribosomes attaching to the ER surface
translocators, signal sequences
exocytosis/endocytosis
p
Properly folded proteins leave the … in a … and go towards …
ER
vesicle
Golgi
Golgi apparatus
sorting ->
- lysosome, eller
- plasma membrane, eller
- secretory vesicle
The lysosome
A lysosome is a membrane-bound cell organelle that contains digestive enzymes. Lysosomes are involved with various cell processes. They break down excess or worn-out cell parts.
Phagocytic cells
Phagocytic cells can engulf and degrade entire cells
