Membrane Permeability (session 3) Flashcards
What is a semi-permeable membrane?
Layer through which only allowed substances can pass
Which cells have more Na+/K+ ATPase pumps?
Neurones
What does passive transport depend on?
Permeability and concentration gradient
What are the roles of transport processes? (6)
Maintenance of ionic composition (protons and carbonate)
Maintenance of intracellular pH
Regulation of cell volume
Concentration of metabolic fuels and building blocks
Expulsion of metabolic waste products and toxic substances
Generation of ion gradients necessary for electrical excitability of nerve and muscle
What is a more accurate way of determining the Vmax and Km?
Double reciprocal plot (line weaver plot)
Define Vmax
Maximum velocity at which enzyme catalyses a reaction
Define the Michaelis constant, Km
Substrate concentration at 1/2 the maximum velocity
Which cells spend up to 30-50% of their ATP on active transport?
Nerve cells Muscle cells Erythrocytes Enterocytes (cell of intestinal lining) Hepatocytes
Give an example of a primary active transporter
PMCA
What is uni-transport?
Only one molecule is transported at a time
What is co-transport?
More than one type of ion or molecule may be transported on a membrane transporter per reaction cycle
What are the two types of co-transport?
Symport-transports two different substances in the same direction
Antiport-transports two different substances in opposite directions
What percentage of the basal metabolic rate is used to keep the Na+/K+ ATPase pump working?
25%
Why is the sodium pump called a P-type ATPase?
Because ATP phosphorylates aspartate, producing a phosphoenzyme intermediate
What leads to a high intracellular [K+]?
3Na+ expelled for every 2 K+ that enter
What are the properties of a primary Ca2+ transporter?
Ca2+/Mg2+ ATPase = high affinity, low capacity, uniport
What are the properties of a secondary Ca2+ transporter?
Na+/Ca2+ exchanger (NCX) = low affinity, high capacity, antiport
What are three examples of antiport transporters?
Na+/K+ ATPase
NCX
Na+/H+ exchange
What is an example of a symport transporter?
Na+/glucose co-transport in the small intestine and kidney
What is the transporter in cystic fibrosis called?
Cystic Fibrosis Transmembrane Conductance Regulator (CFTR)
What are the three types of transport?
Diffusion
Facilitated diffusion
Active transport
