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Biostructures energetics and synthesis > Williamson - Membranes > Flashcards

Williamson - Membranes Flashcards

1
Q

what is a membrane raft, which phospholipids

A

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

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2
Q

what proteins associate with membrane rafts

A

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

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3
Q

how can you find membrane rafts

A

AFM (atomic force microscopy)

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4
Q

what can a membrane raft do

A

organise proteins
signal
trafficking - endocytosis

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5
Q

how does endocytosis occur

A

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

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6
Q

what does patch clamping measure

A

the current across a membrane

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7
Q

what does inside out patch clamping geometry measure

A

current across the patch of inner leaflet membrane

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8
Q

what does outside out measure

A

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

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9
Q

what does whole cell geometry patch clamping measure

A

current across the whole cell

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10
Q

what is the concentration of sodium inside and outside the cell

A

inside: 12mM
outside: 150 mM

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11
Q

what is the concentration of potassium inside and outside the cell

A

inside: 140 mM
outside 4 mM

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12
Q

when is the peak of action potential

A

when sodium channels close and potassium channels open

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13
Q

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

A

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

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14
Q

what causes a cell to be hyperpolarised

A

a rush of K+ out of the cell

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15
Q

how would you characterise a voltage-gated channel

A

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

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16
Q

how would you characterise a ligand gated channel

A

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

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17
Q

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

A

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

18
Q

what is the refractory period

A

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

19
Q

what is hyperpolarisation

A

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

20
Q

what is repolarisation

A

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

21
Q

what is depolarisation

A

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)

22
Q

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

A

ATP powering the Na+/K+ pump

23
Q

what are the structure features behind a voltage-gated channel

A

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

24
Q

why is the potassium leak channel important

A

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

25
Q

what is the equilibrium potential

A

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

26
Q

what does a myelin sheath do

A

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

27
Q

what is a single pass G protein

A

Ras

28
Q

what is a heterotrimeric G protein

A

the Gαβ𝛾 complex

29
Q

Outline the mechanism of activation of the acetylcholine receptor

A

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

30
Q

what is a second messenger

A

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

31
Q

Gαs

A

stimulatory, ATP → cAMP → kinase cascade

32
Q

Gαi

A

inhibits ATP → cAMP → kinase cascade pathway

33
Q

Gαq

A

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

34
Q

What is a kinase cascade?

A

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

35
Q

how can signals cross the cell membrane

A

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

36
Q

what does grb2 contain and what is it analogous to

A

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)

37
Q

what does Sos contain

A

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

38
Q

How is a GPCR turned off

A

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

39
Q

cholera

A

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

40
Q

whooping cough

A

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

41
Q

high pKa

A

hydrophobic = protonated

Biostructures energetics and synthesis (4 decks)

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