membrane protein transporters Flashcards
simple diffusion
nonpolar compounds only, down concentration gradient
facilitated diffusion
down electrochemical gradient
primary active transport
against electrochemical gradient, driven by ATP; solute accumulation is coupled directly to an exergonic chemical reaction
secondary active transport
against electrochemical gradient, driven by ion moving down its gradient; endergonic transport of one solute is coupled to the exergonic flow of a different solute that was originally pumped uphill by primary active transport
ion channel
down electrochemical gradient; may be gated by a ligand or ion
ionophore-mediated ion transport
down electrochemical gradient
classes of transporters
uniport, cotransport (symport & antiport)
GLUT1
ubiquitous; basal glucose uptake
GLUT2
liver, pancreatic islets intestine; in liver and kidney, removal of excess glucose from blood; in pancreas, regulation of insulin release
GLUT3
brain(neuronal), testis(sperm); basal glucose uptake
GLUT4
muscle, fat, heart; activity increased by insulin
SERCA pump
each catalytic cycle moves two Ca2+ ions across the membrane and converts an ATP to ADP & Pi; two conformations of the transporter, E1 & E2, interconvert
ABC transporters (ATP-Binding Cassette)
pump out of the cell against a concentration gradient (toxins & drugs)
multi-drug transporter confers drug resistance to anti-tumor drugs
overexpression of MDR1 is associated with treatment failure in cancers of the liver, kidney, and colon
multidrug transporter (MDR1)
human ABC transporter with very broad substrate specificity
-> encoded by the ABCB1 gene
-> removes toxic compounds
-> responsible for resistance of tumors to drugs
secondary active transporters
use transport down a gradient to provide energy for transport against a gradient
