lec 7 memb transport

4 different mechanisms used to move solutes across membrane? describe the 2 main ones

PASSIVE (simple + facilitated) along conc gradient (no energy)

ACTIVE (primary + secondary) against conc gradient (needs energy input, often ATP, transport proteins needed!!)

what 2 things does simple diffusion require

1. membrane permeability

2. favourable gradient conditions

what 3 things are permeability determined by? properties of solute

1. molecular SIZE (small faster)

2. particient coefficient (measure of POLARITY) (greater lipid solubility = faster penetrate memb)

3. CHARGE (memb impermeable to ions)

what is simple diffusion and what is it possible for

-UNASSISTED movement down conc gradient

-gas

-nonpolar molec (hydrophobic)

-SMALL polar molec (water, glycerol, ethanol)

example of simple diffusion in the body?

-O2 inhaled by lungs and taken up by erythrocytes

-in capillaires of BODY TISSUES, low O2 + high CO2 relative to erythrocyted (O2 RELEASED from Hb and diffuses OUTWARD to tissurs)

-in capillaries of LUNGS, high O2 + low CO2 relative to erythrocytes (O2 diffuses INWARD and binds Hb)

simple diffusion vs osmosis

simple diffusion: memb PERMEABLE to solute. solute moves from high to low solute conc

osmosis: memb NOT permeable to solute, so water move from low to high solute conc

what are 2 main classes of FACILITATED diffusion transports

1. Channel proteins (form Hydrophillic channels thru membrane - allow solutes thru without major conformational change)

2. Carrier proteins (bind atleast 1 solute molecule, undergo conformational change that transfer solutes to other side)

what are 3 kinds of channel proteins (facillitated diffusion)

1. Aquaporins (increase water permeability of memb)

2. Porins (passage of various hydrophillic solutes determined by PORE SIZE)

3. Ion channels (HIGHLY SPECIFIC)

do cells swell or shrink when in hypotonic solution? how is this different for frog oocytes?

swell

-frog oocytes: swell then BURST

how is aquaporin structure selective for water

hydrophillic aa’s side chains + carbonyl groups in MIDDLE of channel form H bonds w/ transported water molecules

where are porins found? whats their structure like?

-PORINS found on outer memb of mitochondria, cholorplasts, bacteria

-structure: cylindrical B-barrel with water pore at center

-on B-barrel:

- polar side chains line inside

-outside, nonpolar side chains point INTO membrane

diffusion (passive transport) depends on electrochemical gradient, so what does it depend on for no charge molec vs ion

no charge: depends on conc gradient only

ion: depends on electrochemical gradient (electic potential plus conc gradient)

is facilitated diffusion including ion channels bi or uni directional

BI so molec can go in and out

how specific are ion channels

usually only for ONE specific ion like Na+ or Cl-

what are the 3 gates talked about in this course for ion channels and describe what they respond to

Voltage-gated: respond to changes in memb potential

Mechanically gated: respond to mechanical forces on memb

Ligand-gated: respond to binding of specifib substance (one type extracellula, one type intracellular)

ion channels are very selective. how does a K+ channel let in K+ but not Na+

-in the filter, the ions lose hydration

-carbonyl oxygens attach to dehydrated K+, which gives back energy

-Na+ too small to interact with carbonyl oxygens so loses lots of energy to enter filter

what model do carrier proteins use? what are the 2 conformational states

-alternating conformation model

1. solute-binding site open to one side of memb

-solute binding cause protein to change to other conformation

2. solute-binding site open to OTHER side of memb

-then solute released