Lecture 14 Flashcards

Question

Describe voltage gating in K+ channels.

Answer 1

-- voltage gating is provided by a positively charged domain at the bottom of the channel structure (usually filled w/ positively charged amino acids) -- S4++ domain form voltage sensing paddles that can occlude (close) the channel -- close channel: S4++ domain "down position" -- on membrane depolarization inside become +++, electrostatic repulsion of S4++ paddles upward: channel opens -----------------------> this is because repulsion occurs by charge inside cell because they are already positive

Answer 2

True; both phosphorylation and dephosphorylation

Answer 3

- - Regulation of Ca2+: important for cell signaling | - - Regulation of Na+/K+: important for membrane potential

Answer 4

- - requires work, usually provided by hydrolysis of ATP - - necessary to move substances across concentration gradient ``` #1.) Protein (4 subunits) is open to interior of cell and binds Na+ ATP phosphorylates protein #2.) conformational change. Open to outside, doesn't bind Na+, but does bind K+. P is hydrolyzed, giving Pi #3.) Goes back to original form, no longer binds K+, which enters the cell. More Na+ can now bind ``` -- pumps Na+ out despite low concentration inside cell; pumping K+ in despite high concentration inside cell

Answer 5

- - also uses ATP to move things against their gradient - - 1 transmembrane domain and 2 ABC - - 1 molecule transported for 2 ATP hydrolyzed -- binding of specific substrate induces steric fit that enhances affinity for ATP

Answer 6

-- multi-domain transport proteins -- have 2 cytosolic ATP-binding sites (cassette) -- small molecules, like drugs, can be transported across the membrane -- drug efflux pumps involved in multidrug resistance of cancer cells

Answer 7

-- multi-drug resistance protein (MDR) ejects pharmacological agents, such as those used in cancer treatments

Answer 8

CTFR = Cystic Fibrosis Transmembrane Regulator -- mutations in CFTR gene (usually in NBD 1) cause Cystic Fibrosis -- the channel normally transports Cl- across cell membrane -- non-functional, Cl- secretion is decreased, leaders to formation of viscous mucus

Answer 9

- - Antiporter = transport of 2 solutes in opposite directions (1 moving in and 1 moving out) - -Symporter = transport of 2 soluetes in same direction (both moving in or both out )

Answer 10

-- transport of single solutes following concentration gradients

Answer 11

- - uses ion gradient that forms from a uniport system - - the flow of ions down a gradient can be used to perform work -- high concentration of Na+ from outside the cell can flow back inside and bring glucose along with it when BOTH are present in lumen of intestine (concentration is high in lumen so it's unfavorable); it can transport glucose against concentration gradient by using potential energy of Na+ gradient Note = bringing in glucose is unfavorable;

Answer 12

-- neurons have specialized projections, called dendrites and axons that act as the wires of the system -- signals must be conducted over long distances very quickly -- it accomplished this by waves in the membrane electrical potential on the membrane surface -- basic idea is that we want to move a signal from where it's received and transmit it along a pathway

Answer 13

-- influx of Na+ results in a change in voltage and activates voltage-gated channels along the axon -- and finally activate voltage-gated Ca2+ channel to release neurotransmitter at presynaptic terminal

Answer 14

-- acetylcholine receptors -- responsible for electrochemical signal transduction at synapses -- expressed at postsynaptic membrane. Respond to acetylcholine released by massive vesicle fusion at the presynaptic membrane -- binding of acetylcholine triggers opening of this non-selective channel (let both Na+ and K+ ions through)

Answer 15

-- generated in neurons by membrane depolarization involving Na+ and K+ ion channels

Answer 16

-- voltage gating: a channel will open given a specific change in membrane potential -- ligand gating: a channel will open upon binding of a specific ligand -- for both types of gates, stimulus (voltage or ligand) induces a change in channel conformation that leads to opening

Answer 17

- - sudden rise in Na+ ion influx | - - 40 mV

Answer 18

1- Steady state membrane potential (-60 mV) achieved and maintained by Na+ and K+ ion pumps (with ATP) 2- Firing of neuron leads to acetylcholine release in synaptic cleft 3- Binding to acetylcholine receptors and opening of ligand gated channels 4- Entry of Na+ and exit of K+ ions (chemical gradient) towards ~ -20 mV (Veq) 5- At ~ -40 mV voltage gated Na+ channels open and depolarization accelerates with high Na+ influx 6- After a few ms Na+ channels inactivate, and K+ channel open. Action potential reach its max. 7- With efflux of K+ action potential decrease rapidly, until K+ inactivate. 8- Slight overshoot in K+ (resting potential below -60mV) is slowly corrected by active pumping of Na+ and K+

Lecture 14 Flashcards

(50 cards)