Membane Transport Flashcards
concentration of ions
K+ is high in the cell, Na, Cl and Ca are high outside the cell
4 functional classes of transmembrane proteins
- transporters
- anchors,
- receptors
- enzymes
what is a protein transporter?h
has moving parts, transfers molecules from one side of the membrane to the other by changing its shape
what is a channel protein?
forms hydrophilic pres in the membrane that allow for passage of small molecules/ions down its concentration gradient, discriminate based on size and electric charge (channel mediated passive transport)
passive transport
molecules move down their concentration gradient, high to low, NO ENERGY NEEDED
active transport
molecules move against concentration gradient, requires energy
examples of channel-mediated passive transport?
aquaporin, selectively transports water molecules bidirectionally, regulates cell volume and internal osmotic pressure
what is transporter mediated passive transport?
transporter transitions between 2 states randomly and independent of whether solute is bound or not, so the solute moves down its concentration gradient, NO ENERGY REQUIRED
example of a type of transporter mediated passive transport?
GLUT uniporter
what is an electrochemical gradient?
concentration gradient of solute PLUS voltage against membrane
3 methods of active transport
- coupled transporters
- ATP-driven pumps
- light driven pumps
what is a coupled active transporter?
couples the transport of 1 molecule DOWN its concentration gradient with the transport of another molecule UP its concentration gradient
what is ATP driven pump?
couples transport of molecules against their concentration gradient with ATP hydrolysis
what is a symport
both molecules are transported in the same direction across the membrane
what is an antiport?
molecules are transported in opp directions across membrane
examples of symporters?
Na-glucose symport (SGLT1 and 2), couples transport of Na ions DOWN its concentration gradient with transport of glucose AGAINST its concentration gradient
where are SLGT1 symporters found?
in the small intestine epithelial cells for glucose absorption
where are SLGT2 symporters found?
proximal tubules of the nephron in the kidney for glucose reabsorption
2 glucose transporters in the enterocytes in intestinal mucosa?
sodium dependent glucose transporter (SGLT1) on the apical surface, passive glucose transporter on basal surface (GLUT uniporter)
explain glucose uptake in the intestinal mucosa
glucose concentration highest in the intestinal epithelium lowest in the gut lumen and ECF, this is why SGLT1 is required for glucose uptake into the cell in intestine, and only GLUT uniporter required from cell into ECF
explain SGLT2 inhibitors
they are used to treat DM2, because it inhibits SGLT2 transporters in the proximal tubule cells in the kidney, limiting glucose reabsorption, resulting in the expulsion of glucose into the urine
SGLT2 inhibitor ex
invokana, farxiga
example of active antiporters?
Na-Ca exchanger in the plasma membrane
action of Na-Ca exchanger (NCX)?
helps regulate intracellular Ca levels, uses energy of Na (3) movement down its electrochemical gradient into the cells to move Ca (2) out of the cell against its concentration gradient
How is the level of Ca in a cell regulated?
NCX and Ca pumps (both active transport - NCX energy from electrochemical gradient, Ca pump from ATP -2 per ATP)
Why is it important to regulate Ca levels inside the cell?
Ca acts as a second messenger in signal transduction pathways, so it needs to be at a low level inside the cell
How are Na and K concentrations regulated?
Na-K pump in the plasma membrane, requires ATP and is responsible for 1/3 of the cell’s energy expenditure (2/3 of neuron expenditure)
why is important to regulate Na and K levels in the cell?
it maintains the negative (-70) resting potential of the cell for correct action potentials (influx of Na into the cell, K exflux)
Action of the sodium potassium pump ?
pump moves 3 Na out of the cell, moves 2 K into the cell (against concentration gradient)
how does the Na-K pump regulate glucose absorption in the intestinal mucosa???
keeps intracellular Na concentrations low, so that the electrochemical gradient is maintained (for Na ions to move into the cell through the SGLT symporter on the apical side)
what are ABC transporters?
ATP binding cassette transporters, active transporters using the energy released from ATP hydrolysis to move substrates against their electrochemical or concentration gradients, most are effluxers
What do ABC transporters transport?
some are ion channels, some transport metabolic products, some drugs, lipids, and sterols, most are EFFLUXERS
What transporters are responsible for some forms of multidrug resistance and why?
ABC transporters such as ABCB1 and ABCG2, because some cancers upregulate these ABC transporters spit some drugs back out of the cell
pathology of cystic fibrosis?
mutation in CFTR (cystic fibrosis transmembrane conductance regulator)
what does the CFTR protein do?
member of ABC transporter, Cl and bicarbonate transporter,
3 types of gated ion channels?
voltage gated, ligand gated, stress gated
why are voltage gated ion channels important?
propagation of electrical signals in nerve, muscle and egg cells
which voltage gated channels are responsible for creation and propagation of AP?
voltage gated Na channels
which voltage gated channels are responsible for muscle excitation and contraction?
voltage gated Ca channels
which voltage gated channels are involved in repolarization after AP?
voltage gated K channels
What is unique about ligand gated ion channels?
it converts a chemical signal into an electrical signal by opening channels for entrance or exit of specific ions
example of ligand gated ion channel?
nicotinic acetylcholin receptor (nAChR), found on the surface of some neurons and postsynaptic side of NMJ
action of aAChR?
binds acetylcholine, allows for influx of Na and outflow of K along their electrochemical gradients, changing the membrane potential in the postsynaptic cell (influx of Na causes membrane potential to become more positive)
action of gated ion channel in activation of synapses
voltage gated ion channels open in response to AP, allowing influx of Ca. increase of calcium in the cell induces release of NT into the synaptic cleft. NT binds to ligand gated ion chnnels on postsynapse, resulting in change in membrane potential in postsynaptic cell
how is the resting membrane potential maintained
K leak channels, and (Na-K pump)
example of stress gated ion channels
auditory hair cells’ stereocilia on surface
how do stereocilia work?
stress gated ion channels on one stereocilia are connected to stress gated ion channels on the adjacent stereocilia, the sound vibrations cause basilar membrane to vibrate, the stereocilia to tilt and the stereocilia open the stress gated ion channels causing ions to flow into the hair cells and an electrical signal to the auditory nerve
what type of transporter is GLUT?
uniporter
what type of transporter is SGLT?
symporter
what type of transporter is Na-K and Na-Ca?
antiporters
what type of channel is K leak channel?
non gated ion channel
