Lecture 17 Flashcards
Non mediated transport does ___
not directly use a transport protein
Mediated transport uses a ____
transport protein
Passive transport
moves substances down their concentration or electrochemical gradient
Active transport uses
energy to drive substances against their concentration or electrochemical gradient
Non mediated transport is important for
absorption of nutrients. Excretion of wastes. Nonpolar, hydrophobic molecules.
Ionic selectivity
Property of channels.Specific amino acids lining the pore determine the selectivity of the channel to ions.
Gating
Property of channels. Gates control the opening and closing of the pore.
Stimuli that control gating:
Ligand binding, cell volume, pH, pphosphorylation
Glucose transport occurs until _____
all binding sites are saturated
Facilitated diffusion of glucose (3 steps)
- Glucose binds to transport protein
- Transport protein changes shape. Glucose moves across cell membrane but only down conc. gradient.
- Kinase enzyme reduces glucose concentration inside the cell by transforming glucose into glucose-6-phosphate
Primary active transport:
-Energy is directly derived from the hydrolysis of ATP.
Secondary active transport:
-Energy stored in the ionic concentration gradient is used to drive the active transport of a molecule against its gradient.
Primary active transporters:
Na/KATPase, Ca/KATPase, H/KATPase. 3 Na+ ions removed from cell, 2 K+ ions are brought into the cell. Electrogenic
Na+ and K+ concentrations in the cytosol:
Low conc. of Na, and high conc. of K+ in the cytosol.
Pump-leak hypothesis:
Na and K are continually leaking back into the cell, which ensures the pump works continuously
