Membrane Transport II: Active Transport (18) Flashcards
active transport
pumping of ions or molecules through a membrane against their concentration gradient
low to high concentration
what does active transport always require?
trans-membrane PRO, transporter
what are 3 common things among all active transport PROs?
Specific for a given chemical
Presence in PM is regulated by the cell
When required, vesicles place on PM & then remove them
Transport is coupled to the consumption of E
what is the E source used in active transport?
ATP
what is the diff b/w direct & indirect active transport?
Direct binds to ATP & indirect doesn’t
direct active transport
transporter binds ATP directly & uses the E of its hydrolysis to drive active transport
indirect active transport
transporter uses E already stored in the gradient of a directly-pumped ion
what causes the cell to be slightly negative?
high K+ inside
High Na+ outside
sodium potassium ATPase pumps more positive ions out than what is brought in
sodium potassium ATPase
enzyme & a transmembrane PRO that establishes the gradient of K+ & Na+ ions
Uses ATP to pump out 3 Na+ & pump in 2 K+ against their concentration gradients
electrogenic pump
unequal transport of charged particles
steps of sodium potassium ATPase
- Transporter has a high affinity for Na+ & low affinity for K+, 3 Na+ ions bind to the transporter (inside the cell)
- ATP is hydrolyzed, phosphate is transferred onto the PRO
- PRO conformation changes & opens up allowing Na+ to be released into the ECF. Ion affinity changes, high affinity for K+ & low affinity for Na+
- Binds 2 K+ from outside the cell
- Phosphate is removed from the PRO allowing K+ ions to be expelled into the cell
- Conformation changes to original state, K+ ions are released inside the cell
what is the importance of the sodium-potassium ATPase?
Creates a net charge across PM –> resting potential (prepares for nerve impulses & muscle contractions)
Osmotic balance –> Na+ outside the cell draws water out of the cell (prevents cell from bursting, natural tendency for water to move in since the cell has a high concentration of macromolecules)
Na+ gradient provides E to run several types of indirect pumps
1/3rd of all E generated in animal cells is consumed to run this pump
when is H+/K+ ATPase used? & How does it work?
Used to secrete gastric juice, transports H+ in the gastric juice producing a pH close to 1
Food in stomach triggers histamine to bind to cells, H+/K+ is translocated from vesicles to the PM
H+ pumped out of cell into lumen of stomach & K+ pumped into the cell
when is Ca2+ ATPase used? & how does it work?
Resting = higher concentration of Ca2+ inside the SER than cytosol
Contraction = activation of myosin allows Ca2+ to pass by facilitated diffusion into the cytosol triggering the contraction
Ca2+ ATPase recovers Ca2+ back into the SER to prepare for another contraction (keeps cytosol concentration low)
Also located in the PM of all eukaryotic cells to pump Ca2+ out of the cell maintaining the high Ca2+ gradient outside the cell
P-type pump & what are some exs?
transporter get phosphorylated
Ex:
Na+/K+ ATPase
Ca2+ ATPase on SER & PM (muslce contractions)
H+/K+ ATPase (gastric juice)
V-type pump & what are some Exs?
on vacuoles
uses ATP, but transporter isn’t phosphorylated itself. Binds ADP, ATP binds to the transport where a phosphate is cleaved & ADP remains
Ex: H+ pump only
Plant cells fill vacuoles with H+ Animals have them on lysosomes, vesicles & in the kidneys to regulate blood pH Insects use to regulate gut pH
how many ABC transporters are found in the human genome?
48
ABC type pump & when is it used?
ion transporters
All transporters share a unique phosphorylated region “ATP binding cassette” where the ATP binds momentarily in place before hydrolysis can occur
ATP binding causes conformational allowing the substrate to cross the membrane
used to detoxify cells
structure of ABC type pump
Surface binding domain at one surface/domain restricted to a single type of molecule
ATP binding domain at the other surface/domain
how do cancer cells become resistant to drugs?
over-producing ABC transporters that expel the drug from the cell
Due to rapid division
Mutations arise in ABC transporters
With continued chemotherapy the cells have extra copies of ABC transporters
what are the ATPase pump types?
P-type
V- type
ABC type
co-transport
Uses downhill flow of an ion to pump some other molecule or ion against its gradient
Driving ion is usually Na+ with its gradient established by the sodium-potassium pump
symport pumps
driving ion (Na+) & the pumped molecule pass through the membrane pump in the same direction
antiport pumps
driving ion (usually Na+) diffuses through the pump in one direction providing E for the active transport of some other molecule or ion in the opp direction
how does the Na+/glucose co-transporter work?
Glucose & Na+ are taken from the gut lumen –> PM
Na+ moves from a high to low concentration
Glucose moves from a low to high concentration
Symport occurs through the Na+/glucose transporter where the Na+ gradient is used to bring glucose in against its gradient
Glucose & Na+ are taken from the PM –> ECF (blood)
Glucose passively moves through a channel through facilitated diffusion (down the gradient)
Na+ is exported through the Na+/K+ ATPase (against its gradient)
how is cholera’s effect of water loss combatted with the Na+/glucose co-transporter?
feed a sugar-salt solution, osmotic shift will counter cholera
cells will taken in salt & glucose, causing more water to move into the cell
Na+ & glucose will later be released by the cell
what are 2 exs of antiport pumps?
Na+/Ca2+ exchanger
Na+ down its gradient (into cell)
Ca2+ against its gradient (out of cell)
Na+/K+ ATPase:
Na+ against its gradient (out of cell)
K+ against its gradient (into cell)
how is Ca2+ returned to the ECF?
active transport using:
An ATP driven pump like the Ca2+ ATPase of skeletal muscle
&
A Na+/ Ca2+ exchanger, this antiport pump harnesses the E of Na+ ions flowing DOWN their concentration gradient to pump Ca2+ against its gradient
what are the 2 main active transport mechanisms enabling Ca2+ to be transported out of the cell?
Na+/ Ca2+ exchanger
Ca2+ ATPase pump
how does a defective chloride pump lead to cystic fibrosis?
Cl- is pumped into the ECF, water flows with it (osmosis)
This is important to create a watery mucous outlining the lungs
Enables silia to move inhaled particulates out
Mutation leads to not enough of Cl- being pumped out & leads to a gummy mucous
Thick mucous leads to impaired breathing
Can become so thick that it can retard gas exchange
