Biochem CH. 12

membrane characteristics

• fluid structures

• composed of lipids + proteins

• amphipathic; prevent movement of charged molc.

• proteins make it semipermiable

• noncovalent assemblies

• sheet-like strucutre

membrane regulates; what can/can’t pass thru

entry of polar/charged molc

• polar/charged can’t pass freely

• small/hydrophobic readily cross

membranes partition

2 aqueous environ. —> outside & inside of cell/cytoplasm or inside organelle

membranes func for catalysis how

some enzymes in membranes require membranes for func

membranes convey outside signal to inside of cell by

receptor proteins that bind signal molc

phospholipids + glycolipids form

lipid bilayers in aq. solns

formation of membranes is powered by

the hydrophobic effect (polar/non polar components)

membrane processes depend on

fluidity of the membrane

melting temp

temp @ which membrane transitions from highly ordered —> very fluid

melting temp is dependent on

• length of fatty acids in membrane lipid

• degree of cis unsaturation

what helps to maintain proper membrane fluidity in membranes

cholesterol

integral/intrinsic proteins

embedded in the hydrocarbon core of membrane

peripheral membrane proteins

bound to polar heads

common structure of integral membrane proteins

membrane spanning alpha helices

beta strands can be used as another

embedding integral protein

when plotting free energy transfer of amino acid to water on y-axis (residue # on x axis), +G indicates

amino acid is hydrophobic

(oppositie is true; -G = hydrophilic amino acid)

lipids diffuse rapidly into membranes which way

laterally

transverse diffusion/flipflopping is very

slow

2 conditions for small molc to spontaneously cross membrane/simple diffuse

• conc of molc is higher on one side than the other

• molc is soluble/nonpolar in nonpolar solutions

polar molc can diffuse across membrane only thru

protein channel; facilitated diffusion or passive transport

active transport

movement of molc against a conc gradient (low to high), using ATP

transport proteins func

pumps/channels to facilitate flow of small molc across cell membrane

facilitated diffusion

molc moves down its conc. gradient (high to low) thru a transport protein

passive diffusion

simple diffusion from high to low conc.

features shared by facilitated & active transport

• high rate/very specific

• reaches saturation

• competition

• inactivation or regulation

what happens to transport protein after ligand binds/release

transport protein changes conformation

3 types of facilitated or active transport

• uniport

• symport

• antiport

uniport

one substance at a time

symport

two diff molc in same direction

antiport

two diff molc in opposite direction

for active transport, symport & antiport can use what to transport 2nd molc against conc. instead of atp

can use conc. gradient of one of the molecules to allow transport of 2nd

• one molc will always have to use ATP unless going w/ its conc. gradient

what is pumped in Na+-K+ ATPase

• 3 Na+ ions OUT of cell

• 2 K+ ions INTO cell

what is pumped into cell

2 K+ ions

what is pumped out of cell

3 Na+ ions

P-type ATPases get its name from the rxn including an

intermediate in which the enzyme is phosphorylated

how symporters/antiporters power transport of molc against its conc. graident

by coupling the movement to the movement of another molc. down its conc. gradient

ion channels

facilitative transport sys. that allow specific/rapid transport of ions down their conc. gradients

voltage activated channels

activated by changes in voltage across membrane

receptors via receptor mediated endocytosis

bind to signaling molc. & relay info to interior of cell

(ie: LDL)