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Membrane Excitability > Membrane Structure and Function > Flashcards

Membrane Structure and Function Flashcards

1
Q

What 3 components make up biological membrane?

A

lipids, proteins and carbohydrates

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2
Q

how are lipids arranged in biological membranes?

A

lipid bilayer

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3
Q

What’s the fluid mosaic model?

A

model of the lipid bilayer, emphasises fluidity with few proteins floating around

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4
Q

what does the evolved fluid mosaic model emphasise?

A

ordarrrrrrr

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5
Q

what determines the fluidity of the membrane?

A

composition of lipid chains determines fluidity of membrane

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6
Q

what’s more fluid long or short fatty acid chains?

A

short

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7
Q

what forms kinks in fatty acid chains?

A

cis-bonds

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8
Q

what do kinks in fatty acid chains do?

A

mean chains can’t pack so closely together, therefore increases fluidity

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9
Q

are cis bonds natural in fatty acids?

A

yes

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10
Q

are trans bonds natural in fatty acids?

A

no

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11
Q

when classifying membrane lipids by head groups, what are the 3 types?

A

phospholipids
glycolipids
cholesterol

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12
Q

how are lipids distributed in the bilayer?

A

asymmetrically

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13
Q

what generates the lipid asymmetry?

A

flippase

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14
Q

what is flippase?

A

an ATP pump/ ATPase

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15
Q

what is the outer-leaflet of the membrane?

A

the part on the extracellular side- (cell-cell contact)

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16
Q

what does the outer leaflet usually contain (3)?

A

PC (phosphotidylcholine), SM (sphingomyelin) (these are phospholipids) Glycolipids

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17
Q

what is the inner-leaflet of the membrane?

A

on the intracellular side (contact with cytoplasm- involved in signalling in cell)

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18
Q

what does the inner leaflet contain?

A

PE (phosphotidylethanolamine), PI (phosphotidylinositol) and PS (phosphotidylserine)- all phospholipids

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19
Q

what causes the loss of lipid asymmetry?

A

inhibition of flippases
or
acctivation of scramblases

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20
Q

what does loss of assymetry do?

A

affects cellular signals e.g. PS on outer leaflet would cause phagocytosis of cell

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21
Q

what’s the function of phospholipid in membrane lipid?

A

signaling and structure

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22
Q

what’s the function of cholesterol in membrane?

A

increases stability and reduces permeability

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23
Q

what’s the function of glycolipid in membrane?

A

cell recognition and protection

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24
Q

what’s the ratio by number of lipid molecules to proteins?

A

50:1

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25
Q

what’s the mass percentage of proteins in lipid membrane?

A

30-45%

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26
Q

what are the 3 functions of membrane protein?

A

structure
biochemical reactions
signaling/communication

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27
Q

what are the 2 main classes of membrane protein?

A

integral and peripheral

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28
Q

what are the 2 classes of integral protein?

A

transmembrane and anchored

29
Q

what are the 2 types of transmembrane protein?

A

single pass

multi-pass

30
Q

what are the 3 types of anchored protein?

A

embedded
GPI factor
lipid chain

31
Q

what does the GPI protein do?

A

anchors protein to outer leaflet of plasma membrane

32
Q

what are lipid chain anchored proteins used by?

A

kinases- involved in growth/division of cell

33
Q

what 2 regions do transmembrane proteins have?

A

polar region

non-polar region

34
Q

where are membrane lipids synthesised?

A

ER

35
Q

how do membrane lipids get from the ER to the plasma membrane?

A

trafficked in membrane vesicles which fuse into the plasma membrane

36
Q

where are membrane proteins synthesised?

A

rER

37
Q

what does SRP stain for?

A

Signal Recognition particle

38
Q

what does the SRP do?

A

signals the protein to the membrane and allows the protein to travel through the membrane

39
Q

what sequences do transmembrane proteins have?

A

start- transfer and stop-transfer sequences- for single and multi-pass proteins

40
Q

In what 3 ways are plasma proteins dynamic?

A
  • can spin about a z-axis
  • can change shape
  • move laterally
41
Q

what are lipid rafts?

A

tightly-packed lipids with ore cholesterol and saturated fatty acid chains, specific proteins

42
Q

why are lipid rafts important?

A

protein trafficking to membrane, endocytosis, exocytosis, signalling complexes
diseases can target lipid rafts e.g. prions

43
Q

what sort of permeability do lipids and gases have to membranes?

A

v. high

44
Q

what sort of permeability does water have to membranes?

A

moderate

45
Q

what sort of permeability do glucose and amino acids have to membranes?

A

low

46
Q

what sort of permeability do ions have to membranes ?

A

none (need proteins)

47
Q

what is overton’s rule?

A

solubility of a substance in oil is proportional to its membrane permeability (this isn’t quite true)

48
Q

what rate- concentration relationship is seen in simple diffusion?

A

linear

49
Q

what rate-concentration relationship is seen in protein mediated ion transport?

A

hyperbolic- it’s saturatable

50
Q

what’s the structure of transport proteins?

A

integral - membrane spanning
AAs in lipid bilayer are lipophilic
AAs in pore region are hydrophobic (charged AAs)

51
Q

describe the structure of voltage-gated K+ ion channels

A

6 TM domains
mostly alpha-helix
H5 segment containing charged AAs- pore

52
Q

what are the 3 classes of membrane transport protein?

A
  • ion channels
  • ion pumps
  • Solute Carriers (SC)
53
Q

what do ion channels do?

A

facilitated diffusion of ions through bilayer

54
Q

what do ion pumps do?

A

transport 1 or more substrate(s) against the concentration gradient using enzymes (ATPase) to hydrolyse ATP to ADP. This is primary active transport

55
Q

what are the 3 main types of ion pumps?

A

P-type
V- type
F- type

56
Q

what are the P-type ion pump?

A

typical ion pumps e.g. Na+,K+ ATPase and flippase enzymes

57
Q

what are F-type ion pumps?

A

pumps that drive ATP synthesis in mitochondria (respiration)

58
Q

what are V- type ion pumps?

A

H+ pumps in cell organelles

59
Q

what do solute carriers do?

A

transport 1+ substrates (at least 1 down gradient, some against)

60
Q

are solute carriers diverse?

A

yes- drug target

2nd most diverse after GPCR

61
Q

which 3 types of transport do SCs use?

A

facilitated diffusion
contransporter/ symporters
exchangers (antiports)

62
Q

what 2 influences affect the elctrochemical gradient?

A

membrane potential

chemical gradient

63
Q

how is the Electrochemical gradient calculated?

A

Vm (membrane potential)- Ex (equilibrium potential)

64
Q

how is equilibrium potential calculated?

A

nernst equation

65
Q

what does the nernst equation do?

A

converts a known chemical gradient to an unknown electrical gradient

66
Q

does water permeablility in membranes work as expected?

A

no- it’s more permeable than expected (water is polar)q

67
Q

what mediates water permeability?

A

aquaporins

68
Q

what are aquaporins?

A

water channels

69
Q

what is Aquaporin 4 linked to?

A

brain inflammation- KO mice show increased survival from stroke

Membrane Excitability (9 decks)

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