Williamson - Membranes

Question 1

what is a membrane raft, which phospholipids

Answer 1

thicker more rigid patch of membrane, contains more sphingolipids and cholesterol

Question 2

what proteins associate with membrane rafts

Answer 2

those with long TM helices
GPI anchors
palmitoyl anchors
NOT prenylated anchors

Question 3

how can you find membrane rafts

Answer 3

AFM (atomic force microscopy)

Question 4

what can a membrane raft do

Answer 4

organise proteins
signal
trafficking - endocytosis

Question 5

how does endocytosis occur

Answer 5

protein dimerises and brings lipid rafts together
caveolin proteins bind to one side (inner) causing a curve
more proteins recruited into coat
pinched at the top

Question 6

what does patch clamping measure

Answer 6

the current across a membrane

Question 7

what does inside out patch clamping geometry measure

Answer 7

current across the patch of inner leaflet membrane

Question 8

what does outside out measure

Answer 8

current across outer leaflet membranes - useful for ligand gated channels - can put ligands in the solution

Question 9

what does whole cell geometry patch clamping measure

Answer 9

current across the whole cell

Question 10

what is the concentration of sodium inside and outside the cell

Answer 10

inside: 12mM
outside: 150 mM

Question 11

what is the concentration of potassium inside and outside the cell

Answer 11

inside: 140 mM
outside 4 mM

Question 12

when is the peak of action potential

Answer 12

when sodium channels close and potassium channels open

Question 13

how does the Na+/K+ pump maintain the resting potential

Answer 13

it pumps 3 sodium out for every 2 potassium in maintaining ratio of sodium to potassium which is much lower that outside the the cell (against their concentration gradients)
inside: 150mM:4mM
outside: 12mM:140mM

Question 14

what causes a cell to be hyperpolarised

Answer 14

a rush of K+ out of the cell

Question 15

how would you characterise a voltage-gated channel

Answer 15

using whole cell patch clamping
vary voltage applied
and measure the currents

Question 16

how would you characterise a ligand gated channel

Answer 16

using outside-out patch clamping
different ligands (and different concs) in the buffer solution
measure current

Question 17

What K+ and Na+ channels/pumps are present in nerve cells

Answer 17

Na/K pump 3 Na+ for 2 K+
voltage gated Na+ channel –> action potential
voltage gated K+ channel –> repolarisation
K+ resting channel

Question 18

what is the refractory period

Answer 18

a temporary period after an action potential when the membrane is unresponsive and unable to generate another action potential. This allows the cell to recover and ensures action potentials propagate in one direction.
Due to plug in sodium channel
4ms

Question 19

what is hyperpolarisation

Answer 19

membrane potential is very negative (-70mV) making the cell less likely to generate an action potential
caused by resting K+ channel

Question 20

what is repolarisation

Answer 20

when sodium channels are closed but potassium channels are open
membrane potential decreases from the peak (action potential)

Question 21

what is depolarisation

Answer 21

change in cell membrane potential, making it more likely to generate an action potential
when the threshold (-55mV) is met and Na+ channels rapidly open - action potential (+30mV)

Question 22

where does the energy come from to maintain the action potential along an axon

Answer 22

ATP powering the Na+/K+ pump

Question 23

what are the structure features behind a voltage-gated channel

Answer 23

voltage sensing domains: eg. charged AAs, undergo structural changes to open or close the channel pore
selectivity filter for their ion

Question 24

why is the potassium leak channel important

Answer 24

to maintain the resting potential
negative inside the cell
K+ can leave, leaving behind a negative charge

Question 25

what is the equilibrium potential

Answer 25

the potential at which there is no net movement of an ion across a membrane it is balanced by the electrical force pushing an ion one way and the concentration gradient pushing it the other

Question 26

what does a myelin sheath do

Answer 26

insulate the axon only allows action potentials to be transmitted at nodes = gaps in the sheath where Na+ channels are travels 100x faster saltatory conduction

Question 27

what is a single pass G protein

Answer 27

Ras

Question 28

what is a heterotrimeric G protein

Answer 28

the Gαβ𝛾 complex

Question 29

Outline the mechanism of activation of the acetylcholine receptor

Answer 29

2 Ach molecules bind to the nAchR causing a conformational change in which the 5 subunits twist, opening the channel for ions

Question 30

what is a second messenger

Answer 30

molecules which transmit signals from cell surface receptors to intracellular targets intermediates between receptor and downstream effects and generated upon receptor activation eg. cAMP, IP3, DAG

Question 31

Gαs

Answer 31

stimulatory, ATP → cAMP → kinase cascade

Question 32

Gαi

Answer 32

inhibits ATP → cAMP → kinase cascade pathway

Question 33

Gαq

Answer 33

stimulatory, phospholipase C releases inositol headgroup from phosphatidylinositol, acts as a signalling molecule

Question 34

What is a kinase cascade?

Answer 34

A sequence of kinases which phosphorylate each other leading to phosphorylation of a transcription factor, amplifies the signal

Question 35

how can signals cross the cell membrane

Answer 35

ion channels, ligand or voltage gated GPCRs receptor linked kinases hydrophobic ligands on cytoplasmic receptors

Question 36

what does grb2 contain and what is it analogous to

Answer 36

an adapter SH2 which binds a phosphate on a receptor linked kinase - specific end of adapter 2 SH3 domains which bind to proline-rich arm of Sos - general end of adapter (binds to general pathway)

Question 37

what does Sos contain

Answer 37

a proline arm which binds the SH3 domains of grb2 and a GEF domain which promotes Ras GDP --> GTP --> signal

Question 38

How is a GPCR turned off

Answer 38

receptor is phosphorylated by GRK arrestin is recruited - turns off receptor endocytosed, ligand removed, phosphate removed

Question 39

cholera

Answer 39

ADP-ribose binds to Gαs cAMP continuously made Cl- out of CFTR --> diarrhoea

Question 40

whooping cough

Answer 40

ADP-ribose binds to Gαi inhibitory response turned off too much cAMP made

Question 41

high pKa

Answer 41

hydrophobic = protonated