Membrane Structure and Function

Question 1

What 3 components make up biological membrane?

Answer 1

lipids, proteins and carbohydrates

Question 2

how are lipids arranged in biological membranes?

Answer 2

lipid bilayer

Question 3

What’s the fluid mosaic model?

Answer 3

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

Question 4

what does the evolved fluid mosaic model emphasise?

Answer 4

ordarrrrrrr

Question 5

what determines the fluidity of the membrane?

Answer 5

composition of lipid chains determines fluidity of membrane

Question 6

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

Answer 6

short

Question 7

what forms kinks in fatty acid chains?

Answer 7

cis-bonds

Question 8

what do kinks in fatty acid chains do?

Answer 8

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

Question 9

are cis bonds natural in fatty acids?

Answer 9

yes

Question 10

are trans bonds natural in fatty acids?

Answer 10

no

Question 11

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

Answer 11

phospholipids
glycolipids
cholesterol

Question 12

how are lipids distributed in the bilayer?

Answer 12

asymmetrically

Question 13

what generates the lipid asymmetry?

Answer 13

flippase

Question 14

what is flippase?

Answer 14

an ATP pump/ ATPase

Question 15

what is the outer-leaflet of the membrane?

Answer 15

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

Question 16

what does the outer leaflet usually contain (3)?

Answer 16

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

Question 17

what is the inner-leaflet of the membrane?

Answer 17

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

Question 18

what does the inner leaflet contain?

Answer 18

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

Question 19

what causes the loss of lipid asymmetry?

Answer 19

inhibition of flippases
or
acctivation of scramblases

Question 20

what does loss of assymetry do?

Answer 20

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

Question 21

what’s the function of phospholipid in membrane lipid?

Answer 21

signaling and structure

Question 22

what’s the function of cholesterol in membrane?

Answer 22

increases stability and reduces permeability

Question 23

what’s the function of glycolipid in membrane?

Answer 23

cell recognition and protection

Question 24

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

Answer 24

50:1

Question 25

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

Answer 25

30-45%

Question 26

what are the 3 functions of membrane protein?

Answer 26

structure biochemical reactions signaling/communication

Question 27

what are the 2 main classes of membrane protein?

Answer 27

integral and peripheral

Question 28

what are the 2 classes of integral protein?

Answer 28

transmembrane and anchored

Question 29

what are the 2 types of transmembrane protein?

Answer 29

single pass | multi-pass

Question 30

what are the 3 types of anchored protein?

Answer 30

embedded GPI factor lipid chain

Question 31

what does the GPI protein do?

Answer 31

anchors protein to outer leaflet of plasma membrane

Question 32

what are lipid chain anchored proteins used by?

Answer 32

kinases- involved in growth/division of cell

Question 33

what 2 regions do transmembrane proteins have?

Answer 33

polar region | non-polar region

Question 34

where are membrane lipids synthesised?

Answer 34

ER

Question 35

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

Answer 35

trafficked in membrane vesicles which fuse into the plasma membrane

Question 36

where are membrane proteins synthesised?

Answer 36

rER

Question 37

what does SRP stain for?

Answer 37

Signal Recognition particle

Question 38

what does the SRP do?

Answer 38

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

Question 39

what sequences do transmembrane proteins have?

Answer 39

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

Question 40

In what 3 ways are plasma proteins dynamic?

Answer 40

- can spin about a z-axis - can change shape - move laterally

Question 41

what are lipid rafts?

Answer 41

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

Question 42

why are lipid rafts important?

Answer 42

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

Question 43

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

Answer 43

v. high

Question 44

what sort of permeability does water have to membranes?

Answer 44

moderate

Question 45

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

Answer 45

low

Question 46

what sort of permeability do ions have to membranes ?

Answer 46

none (need proteins)

Question 47

what is overton's rule?

Answer 47

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

Question 48

what rate- concentration relationship is seen in simple diffusion?

Answer 48

linear

Question 49

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

Answer 49

hyperbolic- it's saturatable

Question 50

what's the structure of transport proteins?

Answer 50

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

Question 51

describe the structure of voltage-gated K+ ion channels

Answer 51

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

Question 52

what are the 3 classes of membrane transport protein?

Answer 52

- ion channels - ion pumps - Solute Carriers (SC)

Question 53

what do ion channels do?

Answer 53

facilitated diffusion of ions through bilayer

Question 54

what do ion pumps do?

Answer 54

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

Question 55

what are the 3 main types of ion pumps?

Answer 55

P-type V- type F- type

Question 56

what are the P-type ion pump?

Answer 56

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

Question 57

what are F-type ion pumps?

Answer 57

pumps that drive ATP synthesis in mitochondria (respiration)

Question 58

what are V- type ion pumps?

Answer 58

H+ pumps in cell organelles

Question 59

what do solute carriers do?

Answer 59

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

Question 60

are solute carriers diverse?

Answer 60

yes- drug target | 2nd most diverse after GPCR

Question 61

which 3 types of transport do SCs use?

Answer 61

facilitated diffusion contransporter/ symporters exchangers (antiports)

Question 62

what 2 influences affect the elctrochemical gradient?

Answer 62

membrane potential | chemical gradient

Question 63

how is the Electrochemical gradient calculated?

Answer 63

Vm (membrane potential)- Ex (equilibrium potential)

Question 64

how is equilibrium potential calculated?

Answer 64

nernst equation

Question 65

what does the nernst equation do?

Answer 65

converts a known chemical gradient to an unknown electrical gradient

Question 66

does water permeablility in membranes work as expected?

Answer 66

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

Question 67

what mediates water permeability?

Answer 67

aquaporins

Question 68

what are aquaporins?

Answer 68

water channels

Question 69

what is Aquaporin 4 linked to?

Answer 69

brain inflammation- KO mice show increased survival from stroke