deck_752436 Flashcards
How do small polar uncharged molecules pass though the bilayer?
down their concentration gradient by diffusion.
How do hydrophobi molecules move across the bilayer?
Hydrophobic molecules (O2 and CO2) diffuse across easily.
How do large, uncharged polar molecules pass through the bilayer?
Large, uncharged polar molecules and ions must pass through by transport proteins, again down a concentration gradient.
The smaller the membrane coefficient …
… the larger the net rate of transport
Define secondary transport
transport of a substance is linked to the concentration gradient and transport of another. Usually uses sodium gradient.
What are symports?Give an example of a symport
two molecules move from the same side to another e.g. glucose cotransporter in small intestine
What are antiports and give an example
molecules move to opposite sides e.g. Na/Ca exchange.
What is the purpose of the Na/K/ATPase?
It is necessary for setting up the membrane potential but does not produce the membrane potential – sets up the Na conc gradient that drive the majority of particle transport
Describe some characteristics of Na/K/ATPase
antiport, 3Na for 2K, uses ATP hydrolysis, primary AT = ATP hydrolysis, inhibited by digoxin and ouabain (cardiac glycosides)
Describe PMCA characteristics and what its purpose is
antiport, high affinity, low capacity for Ca, Ca in H out, primary AT = ATP hydrolysis, maintains low intracellular calcium
Describe SERCA characteristics and what its purpose is
antiport, high affinity low capacity for Ca, increase Ca in SR/ER in exchange for H, primary AT = ATP hydrolysis, maintains stores of Ca in SR/ER to prevent cell death
What cellular response does NCX have in ischaemia?
Low ATP levels due to low O2. Na pump inhibited, NCX reverses to lower Ns a conc, high Ca is toxic and activates potent enzymes causing cell death
Describe the characteristics of NCX
secondary AT, 3Na in 1Ca out, current follows Na so not dependent on ATP hydrolysis, involved in ischaemia
Describe the characteristics of NBC
Na and HCO3 into cell and Cl out, follows Na gradient
Describe the characteristics of NHE
uses Na gradient to move H out of the cell, increasing the intracellular pH