Membranes and membrane proteins self-study Flashcards
Which type of membrane has the most protein? The most lipid?
Inner mitochondrial membrane has the most protein. Myelin has the most lipid.
2 major lipid components in eukaryotic cell membranes
- Glycerophopholipids (phosphoglycerids) 2. Sphingophospholipids (sphingolipid containing phosphate)
Gylcerophospholipids
Most abundant lipids of membrane and increase fluidity. Glycerol backbone to which phophoric acid is esterified at alpha C and 2 long chain fatty acids esterified to remaining C atoms. Attachment of phosphate to alpha C makes glycerol symmetric. 2 fatty acyl groups esterified to C1 and C2 of glycerol. 2 long fatty acid chains (carboxylic acids with long chain hydrocarbon side groups) esterified to the 2 remaining C atoms of glycerol (tails)
Saturated vs unsaturated fatty acids
Saturated contains no double bonds (flexible, usually on C1) and unsaturated (usually on C2) contains one or more double bonds
Fatty acid double bonds
Usually cis which puts rigid bend in hydrocarbon chain of unsaturated fatty acids, interfering with packing and reduces van der Waals forces and melting points
Impact of straight fatty acid chains on membrane fluidity
Saturated and unsaturated trans fatty acids decrease fluidity (increase rigidity)
Impact of kinked fatty acid chains on membrane fluidity
Unsaturated cis fatty acids increase fluidity (decrease rigidity). Create pockets containing water and small ions.
Amphipathic
Contain both hydrophilic and hydrophobic components
Micelles
Formed by amphipathic compounds put in aqueous solutions, thermodynamically favorable
5 major groups attached by phosphodiester bridge to glycerol
- Choline 2. Ethanolamine 3. Serine 4. Glycerol 5. Inositol
2 most common glycerol-phospholipids in membranes
- Phosphatidylethanolamine (cephalin) 2. Phosphatidylcholine (lecithin) Have polar heads with no net electric charge at neutral pH
3 membrane molecules with polar heads with negative charge
- Phosphatidylinositol 2. Phosphatidylserine 3. Cardiolipin
Sphingolipids
Amino alcohols sphigosine and dihydrosphingosine are backbones.
Ceramide
Sphingosine with saturated or unsaturated long chain fatty acyl group in amide linkage on the amino group. 2 nonpolar tails.
Sphingomyelin
Phosphorylcholine + Ceramide Most abundant sphingolipid in mammalian tissues. Predominantly on outer leaflet.
Cholesterol in membranes
Compact, rigid hydrophobic molecule. More membrane cholesterol means decreased membrane fluidity. Reduces fluidity near membrane surface.
What membrane has the highest concentration of neutral lipids and sphingolipids?
Plasma membranes
Intracellular membrane lipid makeup
Primarily glycophospholipids with little sphingolipids or cholesterol
Cardiolipin
Found nearly exclusively in the inner mitochondrial membrane
Lipid bilayer fluidity
Individual molecules can move rapidly in their own monolayer but do not readily exchange with adjoining layer (flip-flop)
Lipid bilayer permeability
Essentially impermeable to nonlipid and charged molecules but not to neutral hydrophobic molecules
Membrane protein movement
Move laterally don’t easily flip-flop. Slower than lipids. May be restricted by other membrane proteins they may be attached to (microtubles or microfilaments)
Asymmetric distribution of proteins in membranes
Sphingomyelin predominantly on outer leaflet. Phosphatidylethanolamine mostly on inner leaflet. Cholesterol evenly distributed on both sides.
Integral membrane proteins
Sequences rich in hydrophobic amino acids which interact with the hydrophobic hydrocarbons of the lipids
Peripheral membrane proteins
Located on the cell surface
4 functions of membrane proteins
- Mediators of transmembrane movement of charged/uncharged molecules 2. Receptors for binding hormones/growth factors 3. Enzymes involved in signal transduction 4. Structural to maintain shape
Where is membrane fluidity the greatest?
In the middle (at the ends of the hydrocarbon chains)
Ca2+ ions and fluidity
Decrease fluidity because of interaction with negatvely charged phospholipids
Lipid rafts
Microdomains which move as a unit within outer and inner leaflet of plasma membrane enriched in cholesterol and sphingolipids. Longer and more saturated acyl chains. Thicker, less fluid environment, higher melting temp. Selectively include or exclude proteins. Important for signaling events. Structure regulated by cholesterol; if depleted in cholesterol raft dissociates.
