lecture 18 Flashcards
3 membrane characteristics
involved in receiving info, import and export of molecules, motility (movement)
selective barriers
external and internal (ER, golgi, nucleus)
Hydrophilic molecules form
H bonds with water molecules
Hydrophobic molecules can’t..
form H bonds
predominant lipids in the cell membrane
phospholipids
phospholipids have
a phosphate head
two hydrophobic tails
ampiphatic
one part hydrophobic, one part hydrophillic
lipid bilayers are…
self-sealing
4 characteristics of a lipid bilayer
bilayers eliminate free edges to hide the hydrophobic tails from water
spontaneously form liposomes in the water
bend and adapt to changes in membrane structure
lipids can move laterally but not vertically
fluidity
the ease with which lipid molecules move in the plane of the bilayer
2 properties of the hydrocarbon chain that affect fluidity
- length of chain:
- shorter chain= less tail-tail interaction, increased fluidity
- longer chain= decreased fluidity - number of double bonds:
- saturated= no double bonds, increased fluidity
- unsaturated= double bonds, kink in the chain, decreased fluidity
saturated hydrocarbon chain means
fully saturated w hydrogens, no double bonds, more fluid
unsaturated hydrocarbon chains means
at least one double bond, creates a kink in the chain making it less fluid
what would you do to increase membrane fluidity at colder temp?
increase the number of double bonds in the carbon chain
3 characteristics of cholesterol
- Short, rigid lipid molecules that fill the space (caused by kinks in hydrocarbon tail) between neighbouring phospholipids
- Can stiffen the membrane
- Increases melting point of the membrane
how is the membrane assembled? (where are new phospholipids made?)
new phospholipids are made on the cytosolic side of the ER.
they remain on that monolayer unless they are transferred to the other layer by a protein
What causes the redistribution of phospholipids?
scramblases and flippases
redistribution causes asymmetric distribution of phospholipids
scramblases
randomly move phospholipids from one monolayer to the other
flippases
the golgi membrane has flippases which remove specific phospholipids from one side to the other
which way are cytosolic proteins facing when being transported?
they remain facing the cytosol
name 7 membrane proteins
transmembrane
monolayer-associated alpha helix
lipid linked
protein attached
detergents
integral membrane proteins
peripheral membrane proteins
transmembrane proteins
extend through the bilayer
monolayer associated alpha helix proteins
amphipathic alpha helix embedded in a monolayer
lipid linked protein
attached to the membrane through 1+ covalently linked groups
protein attached proteins
attached to membrane indirectly by association with a membrane protein
detergents
small amphipathic molecules w only one hydrophobic tail
(they form micelles)
integral membrane proteins
need detergents to be removed from the membrane
peripheral membrane proteins
can be removed by gentler procedures
why do detergents form micelles, and phospholipids form liposomes in water?
detergents are wedge shaped
phospholipids are cylindrical
polypeptide chains cross the lipid bilayer with an
alpha helix
single pass
only crosses the membrane one
multipass
crosses the membrane multiple times
beta sheets can cross the membrane as a
beta barrel
cell cortex=
meshwork of fibrous proteins on the cytosolic side of the membrane
animal cells have a cell cortex (rather than a cell wall like plants)
lipids can move freely in the plane unless…
restricted by a membrane domain
tight junctions prevent
diffusion of proteins to other sides of the cell
glycoproteins
proteins w short chains of sugar
proteoglycans
proteins w long chains of sugar
glycocalyx
carbohydrate later, located outside the plasma membrane
- protects cell (slimy) from mechanical damage
- cell-cell recognition and adhesion
