BIOC 503 - MEMBRANE TRANSPORT

simple diffusion

nonpolar compounds only, DOWN diffusion gradient, WITHOUT the help of transporters

facilitated diffusion

diffusion through channel proteins DOWN electrochemical gradient

primary active transport

AGAINST electrochemical gradient

aka pumps

Energy source= ATP hydrolysis directly

secondary active transport

AGAINST electrochemical gradient

aka transporters

energy source = another ion going down its concentration gradient (which itself is maintained by ATP hydrolysis, so indirectly)

electrochemical gradient

Gradient of a solute taking its concentration and electrical charge distribution across the membrane

• always moving towards equilibrium

• driving force 

C02, O2, N2

plasma membrane permeable to small nonpolar molecules like __

dehydrated, activation barrier

all molecules diffusing across the membrane or being transported across via proteins need to first be ____ which causes the process to have a high ___

energy free

diffusion, whether simple (CO2, N2, O2) or facilitated (leaky ion channels) is an ___ process

selective

membrane transport is a ___ process, where transporters are catered towards specific ion sand molecules

gated

ion channels are a specific type of transporter that is often ___ whether by ligand binding, change in membrane potential, or mechanical stimuli.

ATP hydrolysis

Net transport of a molecule AGAINST its concentration gradient (active transport) requires energy via ___, whether directly or indirectly.

energy favorable

NET transport across a membrane must be ____

• depends on solute concentration across membrane

• depends on electrical charge distribution across membrane

Uniport

Transporter of 1 solute in ONE DIRECTION

Ex: K+ channel

symporter

type of transporter of 2 ions in the SAME DIRECTION

antiporter

type of transporter of 2 ions in OPPOSITE DIRECTION

T1, T2

Glucose transporters = family of transporters taking glucose up into the blood/cells

• __ conformation allows glucose to bind on the outside of the cell, causes change in shape

• __ conformation results of change in shape by glucose binding and release it inside the cell, causing change back to original shape

• source of energy = glucose gradient

• UNIPORTER

lactose transporter

• Symporter

• energy source = proton gradient = secondary active transport

• allows lactose to move inside cell

• coupled to proton pump (for energy)

sodium-glucose transporter

• Symporter

• energy source = Na+ gradient = secondary active transport

• 2 Na+ and 1 glucose come into intestinal epithelial lumen from intestine

sodium-potassium ATPase

• Antiporter

• energy source = ATP hydrolysis = primary active transport

• moves 3Na+ out as 2K+ moves in

P-type ATPase

Ex: SERCA which pumps calcium OUT of the cell (Uniporter, primary active transport)

• N domain binding nucleotide ATP

• P domain activated by hydrolyzed phosphate previously ATP bound

• channels open

• A domain = actuator domain = causes dephosphorylation and channel closing and drop of now ADP from N domain

• 6 channel transmembrane domain

• 4 support transmembrane domain

ATP-binding cassette

__ transporters aka ABC transporter moves lipids out of a cell/organelles 

• 2 membrane domain each made of 6 helices

• 2 nucleotide binding domains (NBD)

• 1:1 pumping ratio

cystic fibrosis

Mutation of ABC transporters can cause diseases like ___

V-type

vacuole type ATPase

• pH control in vacuole

F-type

mitochondrial type ATPase

• proton gradient formation/maintenance across inner membrane

• ATP synthase

aquaporins

channels for rapid water movement which are very selective

• uniporter

• energy source = water gradient aka hypotonic pressure

ionophores

small hydrophobic molecules (not proteins) that dissolve into lipid bilayer and increase permeability of specific inorganic ions