WK6 Cell Bio

winniesmith's version from 2017-01-04 18:02

Section 1

Question Answer
What is the speed of transport through an ion channel?more than a million ions per second
Specific channel proteins allow passage of what ions Na+, K+, Ca2+, Cl-
What do ligand-gated channels open in response tooBinding of neurotransmitter or other signalling molecules.
What do voltage-gated channels open in response tooChanges in electric potential across the plasma membrane
How was the role of ion channels transmitting electric impulses made clearBy Hodgkin&Huxley (1952) by using giant squid axons. Electrodes inserted measured changed in potential from open/closing of Na+/K+ channels.
What is the patch clamp technique (Neher & Sakmann 1976) allows activity of individ. ion channels to be studied.
How does the patch clamp technique work? A micropipette is used to isolate a small patch of membrane, allowing the flow of ions through a single channel to be analyzed

Section 2

Question Answer
How do ion pumps maintain concentration gradients use energy from ATP hydrolysis to actively transport ions across the plasma membrane
How is the ionic composition of intra/extrecellular fluids differentIntra- K+ higher (140mM vs 5), extra-Na+ higher(145 vs 5-15) & Cl higher (110 vs 4)
Which ion makes the largest contribution to the resting potential and why?K+. Na+ is pumped in while K+ out, however, membrane also contains open k+ channels
What is the Nernst equation It describes the relationship between ion conc. and membrane potential. V= (RT/zF)ln(Co/Ci)
V=Equilibrium potential in volts
R=gas constant
T=absolute temperature
Z=Charge of the ion
F=Faradays constant (the quantity of electric charge carried by one mole of electrons)
Co and Ci=conc. of ion outside and inside the cell

Section 3

Question Answer
As nerve impulses travel along axons..the membrane depolarizes
What is the threshold value and how fast is it met?+30mV in less than a millisecond
What is the resting potential -60/-70mV
What is the hyperpolarised value-75mV
At the synapse, which type of channel do the neurotransmitters bind tooligand-gated ion channels
What are the ligand-gated channels in muscle cellsNicotine acetylcholine recpetors.
What does the binding of acetylcholine do?induces a conformational change in the receptor. Binding of ACh opens channel allowing rapid influx of Na+, depolarizing the cell membrane=action potential.

Section 4

Question Answer
Size of Na+ and K+Na+ is smaller (O.95 A) than K+(1.33A)
How was the 3D structure of k+ channels determinedby X-ray crystallography.
What is the structure of K+ channelPart of the channel is lined with carbonyl oxygen (C=O) atoms from the polypeptide backbone. They displace the water to which K+ is bound, and the K+ ion passes through. Na+ is too small to interact and remains bound to water
Which ions belong to a family of voltage-gated ion channelsNa+, K+, Ca2+

Section 5

Question Answer
What happens in active transportmolecules are transported against their concentration gradients. Energy is provided by a coupled reaction (such as ATP hydrolysis)
Give an example of active transport The sodium-potassium pump (or Na+-K+ ATPase)
How does the sodium potassium pump work Uses energy from ATP hydrolysis, operated by ATP driven conformational changes.
For one molecule of ATP what does the Na+-K+ pump transport3Na+ out for 2K+ in
What percentage of ATP in animals cells does the Na+K+ pump use?Nearly 25%
Why are the gradients maintained by the Na+K+ pump necessaryfor propagation of electric signals in nerve and muscle cells, to drive active transport of other molecules, and to maintain osmotic balance and cell volume

Section 6

Question Answer
What does the difference in ion concentrations inside/outside cells maintainbalance the high concentrations of organic molecules inside cells, equalizing osmotic pressure and preventing the net influx of water.
What is the Ca2+ pump powered byATP hydrolysis
Why are intracellular Ca2+ concentrations very lowAs Ca2+ is transported out of the cell or into the ER lumen
What are transient,localized increases in intracellular Ca2+ important for?cell signalling (as in muscle contraction)