plamsa membranes

Question 1

channel protein

Answer 1

pores that accommodate size/change of a specific solute

Question 2

gated ion channel

Answer 2

open and close to control ion passage

Question 3

carrier protein

Answer 3

binding sites for solutes, require conformational change

Question 4

passive transport

Answer 4

do not require energy
simple diffusion, osmosis, facilitated diffusion

Question 5

active transport

Answer 5

requires energy
primary requires atp
secondary does not

Question 6

receptors

Answer 6

bind chemical signals

Question 7

second messenger systems

Answer 7

communicate within cell

Question 8

enzymes

Answer 8

catalyze reactions including digestion of molecules

Question 9

carriers

Answer 9

bind solutes and transfer them across the membrane

Question 10

cell identity markers

Answer 10

glycoproteins act as unique tag

Question 11

cell adhesion molecules

Answer 11

mechanically link cell to another cell or to extracellular matrix

Question 12

what is special about channel proteins

Answer 12

they have specificity and use facilitated diffusion (passive)

Question 13

what is osmosis

Answer 13

a specialized form of facilitated diffusion through a channel protein (aquaporin protein channels)

Question 14

what is special about gated ion channels

Answer 14

require a stimulus to transport solutes via facilitated diffusion and have specificity, 3 types (chemically and voltage and mechanically )

Question 15

chemically gated ion channel

Answer 15

chemical messenger (ligand) binds to protein and induces opening
ex : acetylcholine neurotransmitter binds to its receptor on target cell and permits passage of Na and K ions

Question 16

voltage gated ion channels

Answer 16

change in voltage along the length of a neuronal axon induces opening
ex : Na channels opening along axon to allow influx of Na ions

Question 17

mechanically gated ion channels

Answer 17

force on cell membrane physically opens channel
ex: move of fluid in inner ear membrane and opening ip k channels

Question 18

what is special about carrier proteins

Answer 18

carried out by facilitated diffusion or active transport
glucose transporter protein permits transport of glucose
requires conformational change
carrier has a solute binding site and 2 conformational states
bi directional transport and always down glucose concentration gradient

Question 19

what is active transport

Answer 19

requires energy
vesicular transport mechanisms (endo/exocytosis)
carrier transport proteins - coupled transport and atp driven pumps

Question 20

primary active transport (Ca++ ATPase)

Answer 20

driven by atp hydrolysis
in domain the atp and ca are open to cystolic side and ca2+ protein activates atpase
atp is hydrolyzed and P domain is phosphorylated
conformational change and Ca++ is released to SR lumen
ADP and Pi released

Question 21

Primary active transport of Na+ and K+ ATPase

Answer 21

cytoplasmic NA binds to sodium potassium pump

Na binding stimulus phosphorylation by ATP

Phosphorylation causes the protein to change its conformation expelling Na to the outside

extracellular k binds to the protein, triggering release of the phosphate group

loss of phosphate restores the proteins original conformation AND K is released and Na sites are receptive again

Hydrolysis one ATP pump 3 Na out and 2 K into cell

Question 22

secondary active transport - coupled transporters

Answer 22

electrochemical gradient of one solute us used as energy source to pump another solute “hijacking”

Na moves down its gradient
glucose moves against its gradient
both move ecf to ice
SLGLT1 protein uses the Na gradient which was established by the Na-k pump as an energy source to transport glucose

atp hydrolysis used indirectly = secondary active transport

Question 23

membrane potential

Answer 23

all living cells have one

used as a source of potential energy to”do work”
for subset of cells (electrically excitable) membrane

potential be changed for purposes of cell signaling or changing function
membrane potential is between -60 - -90 mV

portion of membrane facing icf is negative

Question 24

how is the membrane potential established?

Answer 24

ion concentration gradient and selective ionic permeability

Question 25

Na-K cell gradient established

Answer 25

Na is being pumped out against it's gradient to get intracellular pool of na established it also must be entering the cell if k is being pumped into the cell against its gradient then the extracellular pool of k is established by k also leaving the cell

Question 26

leak channels

Answer 26

Na doesn't have leak channels bu k does leak channels allow k to move down concentration gradient and exit the cell which contributes to a positive charge on ecf side Na enters cell via coupled transport process membrane has selective ionic permeability for K+ Ecf gains + while icf gains - charge uneven distribution of charge along lipid bilayer electrostatic interactions resting membrane potential

Question 27

sum of Na and K permeability with concentration gradient

Answer 27

ion concentration gradient (Na/K pump) and selective ionic permeability (K leak channels) establish resting membrane potential also need to consider electrochemical gradient and not concentration gradient

Question 28

when k leaves through leak channels (electrochemical)

Answer 28

at equilibrium k is zero but when it leaves chemically downhill high to low electrically uphill negative to positive at equilibrium electrochemical gradient is 0

Question 29

ions move down their concentration gradient until equilibrium is achieved but what are some conditions

Answer 29

steeper gradient = greater tendency of ions to move down gradient stronger electrical field = greater tendency of ions to move down the gradient weaker electrical field = lesser tendency of ions to move down gradient

Question 30

adding potassium to the cell

Answer 30

makes concentration different and more positive and more electrically excitable

Question 31

action potential

Answer 31

changing the membrane permeability to select ions to allow those ions in and out cel is triggered when threshold potential is reached (-40 mV) propagates along the length of the cell membrane membrane permeability is regulated by gated ions

Question 32

synapse

Answer 32

site of communication delivery of neurotransmitters from pre synaptic to post synaptic cell

Question 33

permeability of K and Na inside and outside the membrane

Answer 33

K permeability inside membrane way higher than Na while the opposite on the outside, Na is more permeable

Question 34

What happens when Na gates open in membrane (action potential)

Answer 34

Na flows into the cell and membrane potential becomes more positive = depolarization

Question 35

What happens when Na channels close (action potential)

Answer 35

K channels are open but they are slow and membrane potential becomes more negative = repolarization

Question 36

What happens when K channels are slow (action potential)

Answer 36

K continues to leave the cell and membrane potential becomes more negative than RMP = hyperpolarization

Question 37

steps of action potential

Answer 37

resting potential depolarization peak action potential repolarization hyper polarization

Question 38

as membrane becomes more permeable to Na

Answer 38

membrane potential approaches ENa+

Question 39

Features of voltage gated Na channels

Answer 39

pore forming domains with selectivity filter (specificity for Na ions) voltage sensors enriched in positively charges amino acids inactivation gate "hinge" K channels also have voltage sensors and pore forming domains but no inactivation gate

Question 40

The Na channel has three distinct configurations

Answer 40

- Voltage gated Na channel closed at RMP, negative charge on inside of membrane = inward pull of voltage sensors -Voltage gated Na channel; open at depolarization, slight influx of Na = voltage sensors relax upward = increased Na permeability = greater influx of Na -voltage gated Na channels inactivated quickly - rapid decrease in Na permeability

Question 41

K channels has open and closed configurations

Answer 41

-Voltage gated K channel closed at RMP, negative charge on inside of membrane = inward pull of voltage sensors -voltage gated k channel open at depolarization but opening is slow. Slight influx of Na = voltage sensors relax slowly = increase k permeability lags behind increased Na permeability They are finally open at the time the Na channels are in activated, they are slow to close

Question 42

At each stage when are the channels open or closed

Answer 42

Resting membrane potential - K and Na both closed Depolarization - K slow to open, Na open and influx Action potential - Na inactivated, K slow to open Depolarization - K open and efflux, Na switching from inactivated to closed hyper polarization - K slow to close and inward pull of voltage sensors to close K channels and more negative charge resting memorable potential - K closed and Na switches from inactivated to closed.

Question 43

action potential is unidirectional

Answer 43

when Na channels are inactivated they cannot be opened even with another stimulus

Question 44

what does the action potential do

Answer 44

brings the signal down the axon down the axon of the presynaptic neuron

Question 45

synaptic transmission continues as long as

Answer 45

Action Potential propagates to the synapse membrane receptors are expressed neurotransmitters are available in synaptic cleft

Question 46

what is synaptic transmission

Answer 46

action potential propagates down the axon Na influx and K efflux AP induces opening of voltage gated Ca++ channels in synaptic knob Ca++ enters knob (down its concentration gradient) and induces synaptoagmin (protein associated with synaptic vesicle) to interact with the snare protein complex (at plasma membrane) vesicle membrane fuses with plasma membrane Neurotransmitters are released into the synaptic cleft Neurotransmmiter diffuses across cleft and bind to neurotransmitter receptor Receptor serves as a chemically ligand gated ion channel that opens and permits ion transport across plasma membrane induces localized change in membrane potential (depolarization or hyper polarization, depending on which ion crosses membrane) Localized depolarization triggers opening of voltage gated Na and K channels on adjacent segment of membrane