plasma membrane properties
semipermeable
phospholipid bilayer
fluid mosaic model
glycoprotein coat
created by carbohydrates associated with membrane-bound proteins
phospholipid dynamics
move rapidly in plane of membrane through diffusion
lipid rafts
collects of similar lipids that serve as attachment points for other biomolecules (signaling roles)
flippases
enzymes that assist with flipping of lipids in membrane (energetically unfavorable b/c polar head must be forced into nonpolar region)
components of membrane: lipids, carbs, proteins, nucleic acids - most to least plentiful?
lipids > proteins > carbs > nucleic acids
triacylglycerols
storage lipids - involved in metabolism
unsaturated v saturated fatty acids - effect on fluidity
unsaturated: increase fluidity
saturate: decrease fluidity
chylomicrons
transport essential fatty acids as triglycerides from the intestine
cholesterol structure
hydrophilic and hydrophobic regions; maintains membrane fluidity
waxes
extremely hydrophobic lipids: long-chain fatty acid and long-chain alcohol (waterproofing in plants)
transmembrane proteins
pass completely through bilayer
embedded protines
associated with only one surface of bilayer - catalytic activity linked to nearby enzymes
integral proteins
transmembrane and embedded
membrane-associated (peripheral) proteins
bound by electrostatic interactions or by other proteins - recognition/signaling
carbs on bilayer
generally attached to proteins; hydrophilic - forms coat with water; acts as signaling/recognition
membrane receptors tend to be
transmembrane proteins; activate/deactivate transporters for facilitated diffusion and active transport
cell adhesion molecules (CAMs)
cell-cell junctions made of proteins that allow cells to recognize each other
gap junctions
connexons; allow for direct cell-cell communication; made of protein-surrounded pores that allow movement of water and solutes
tight junctions
physical link between cells as they form a layer of tissue (prevent solutes from leaking into space b/w cells)
desmosomes
anchor cytoskeletons of adjacent cells - formed by interactions b/w transmembrane proteins associated with intermediate filaments
hemidesmosomes
attach epithelial cells to underlying basement membranes
cholesterol fluidity and stability
fluidity - interferes with crystal structure
stability - cross links adjacent phospholipids through interactions at polar head group
passive transport
don't require energy
active transport
need energy input
simple diffusion
substrates move down their concentration gradient directly across membrane
osmosis
simple diffusion of water
hypotonic
surrounding solution is less concentrated than the cell - cell fills with water
mnemonic: hypOtonic - water rushes in and cell forms a big O
hypertonic
surrounding solution is more concentrated than cell - cell loses water
isotonic
cell and surroundings are equimolar - no net movement
osmotic pressure
colligative property (depends on concentration)
osmotic pressure equation
M = molarity
i = van't Hoff factor = number of particles obtained from molecule in sol'n
colligative property
depends only on presence and number of particles in soln, but not their identity
facilitated diffusion
simple diffusion for molecules impermeable to membrane (large, polar, ions) - pass through integral membrane protein transporters/channels
carrier protein
only open to one side at a time - revolving door model: substrate binds outside --> conformational change (occluded state: closed to both sides) --> substrate cross into cell
active transport - concentration gradient?
solute moves against gradient
primary active transport
uses ATP/energy molecule to directly transport molecule
secondary active transport (coupled)
harness energy released by one particle going down its gradient to move desired particle up its gradient
symport
secondary active transport where both molecules move in same direction
antiport
secondary active transport where molecules move in opposite direction
endocytosis
membrane invaginates and engulfs material to bring it into cell (initiated by substrate binding to specific receptors)
pinocytosis
endocytosis of fluids
phagocytosis
ingestion of solids
exocytosis
secretory vesicles fuse with membrane to release material - good for intercell signaling
primary thermodynamic factor responsible for passive transport?
entropy
osmotic pressure and water flow?
sucking" pressure - water moves into compartment with highest osmotic pressure
membrane potential, Vm
difference in potential across cell membranes
usual resting membrane potential
b/w -40 and -80 mV; tends to be nonzero --> must be able to respond to stimuli
leak channels
passive diffusion of ions across cell membrane
sodium-potassium pump (Na+/K+ ATPase)
ion transporter that regulates intra/extracell Na and K concentrations
maintains low Na and high K inside cell (pumps 3 Na out for every 2 K in) - negative membrane potential
Nernst equation
0
Goldman-Hodgkin-Katz voltage equation
*** note Cl- inverted b/c it carries negative charge
outer mitochondrial membrane
highly permeable - lots of large pores for ions and small proteins
inner mito membrane
restricted permeability, cristae = foldings to increase surface area, encloses matrix, contains lots of cardiolipin and no cholesterol
trans glycerophospholipids - effect on fluidity of membrane?
decrease fluidity
movement of solute or water by diffusion or osmosis depends only on?
concentration gradient of THAT molecule and on membrane permeability