Lecture Set 9 Flashcards
What are the different ways to transport molecules across the membrane?
1) simple diffusion –> down concentration gradient, no energy required, small polar, or nonpolar molecules
2) facilitated diffusion –> down concentration gradient, no energy required, uses channel/carrier protein, polar/charged molecules
3) primary active transport –> up concentration gradient, uses hydrolysis of ATP, uses carrier protein
4) secondary (indirect) active transport –> up concentration gradient, uses potential energy gradient (created through primary active transport)
What is the partition coefficient?
equilibrium constant for substance dispersion between oil and water
what does diffusion rate depend on?
concentration gradient, polarity, size
Define a carrier and channel protein?
carrier –> alternates between two conformations
channel –> pore that molecules diffuse through
Describe the general features of carrier proteins
transmembrane
multiple membrane-spanning alpha helix segments
What drives passive transport?
electrochemical gradient –> chemical gradient determines direction, electrical gradient determines speed
Give examples of each type of transport in the erythrocyte membrane
simple diffusion = gases
passive transport through carrier = glucose through GLUT1
passive transport through channel = aquaporin
active direct transport = Na/K
How are transporters like enzymes?
similar reaction kinetics
can experience competitive inhibition
lower activation energy
stereochemical specific binding via weak, non-covalent interactions
What are the 3 types of carrier proteins?
1) uniport –> transfer 1 molecule
2) symport –> transfer 2 molecules in same direction
3) antiport –> transfer 2 molecules in opposite direction
How can channels be gated?
mechanically, chemically, electrically
How does the channel maintain specificity?
ex. K+ is hydrated through 4 bonds, Na+ is too small and is only hydrated by 2 bonds
pore diameter, electrical charge
What are the 4 types of transport ATPases
1) P-class –> two catalytic alpha subunits with ATP binding site, one or two regulatory Beta subunits, phosphorylation of alpha subunit creates conformation change (example = Na/K pump, Ca pump)
2) V-class –> proton transport (maintains acidic environment)
3) F-class –> proton transport, if reversed, can make ATP
4) ABC superfamily –> 4 subunits (2 transmembrane, 2 regulatory) involved in transporting many substrates
Describe the Na/K pump
three Na bind, ATP hydrolyzed, causes shape change and now low affinity for Na, so Na released to exoplasmic environment. pump now high affinity for K, 2 K binds, then conformation change when phosphate released, this causes low affinity for K, so K released to interior
Describe the Na/Glu pump
2 Na bind, causes high affinity for Glu, so Glu binds, causes conformation change, release of na. The causes low affinity for Glu, so release of Glu. Conformation change to now be high affinity for Na. Na gets pumped back outside through Na/K pump
