Week 3: Membrane Mobility

Question 1

What structure does biological memmbrane have?

Answer 1

Liquid crystal structure

Question 2

Lipid crystal structure

Answer 2

Lipid are close packed and relatively high ordered - but free to move in some directions

Question 3

What does cooling the membrane result in?

Answer 3

Phase transition

Question 4

What does the barrier function of the cytoplasmic membrane depend on,

Answer 4

Physical state of lipid bilayers

Question 5

At lower temperature what happens to the membrane lipid bilayers ?

Answer 5

Undergo a reversible change of from fluid to a non fluid array of fatty acyl chains

Question 6

What does changing growth temperature trigger?

Answer 6

Cell responses that change the lipid composition of membranes

Question 7

What is phase transition?

Answer 7

Temperature required to induce a change in lipid physical state from ordered gel phase to disordered liquid crystalline phase

Question 8

What factors control membrane fluidity?

Answer 8

1) saturation/desaturation of fatty acids 2) cholesterol content 3) temperature

Question 9

saturation/desaturation

Answer 9

Introduces bends - desaturated Lipids cannot pack so closely and do not form gels so easily Lipids with shorter chains are less stiff and less viscous Make tails more rigid - cannot rotate easily (membrane more fluid). Phase transition temperature is lowered

Question 10

Cholesterol content

Answer 10

Disrupt packing of fatty acid chain and inhibit the formation of gel state Widens the range at which the membrane stays fluid. Bidirectional regulator At high temperature: stabilises the membrane and raises its melting point Lower temperature: it intercalates between phospholipids and prevent them from clustering together and stiffening

Question 11

Temperature

Answer 11

Heats up the membrane Lipids require thermal energy when heated; energetic Lipids move around more, arranging and rearranging randomly, membrane more fluid

Question 12

What does Cyanobacterium lack the genes for?

Answer 12

Coding for desaturates

Question 13

Desaturases

Answer 13

Enzyme that introduce double bonds into fatty acids

Question 14

Why is membrane fluidity important ?

Answer 14

1) it allows membrane proteins rapidly in the plane of bilayer 2) it permits the membrane Lipids and proteins to diffuse from sites where they are inserted into bilayer after their synthesis 3) it enables membrane to fuse with one another and mix their molecules 4) it ensures that membrane molecules are distributed evenly between daughter cell when a cell divides 5) necessary to allow diffusion and dynamic interaction of proteins in the membrane (cell signalling) 6) diffusion of other membrane compartment 7) membrane assembly

Question 15

What can lipid bilayer exist as?

Answer 15

Relatively fluid state

Question 16

How can phospholipid move?

Answer 16

Laterally within the same leaflet with considerable ease

Question 17

How can the mobility of individual Lipids molecules within bilayer of plasma membrane be observed?

Answer 17

Under microscope by linking the polar heads of the lipid with gold particles or fluorescent compounds

Question 18

What is the half-life of a phospholipid molecule moving across to the other leaflet measured?

Answer 18

Hours to days

Question 19

What movement of phospholipid is more restricted?

Answer 19

Flip flop to other side of the membrane

Question 20

How does flip flop occur?

Answer 20

The hydrophilic head group of lipid must pass through the interval hydrophobic sheet of membrane which is thermodynamically unfavourable?

Question 21

What enzymes actively move certain phospholipids from one leaflet to the other?

Answer 21

Flippases

Question 22

What does the enzyme establish?

Answer 22

Lipid asymmetry and reverse the slow rate of passive transmembrane movement

Question 23

What are the heterogeneity in Membranes?

Answer 23

1) Asymmetric distribution of Lipids in the two bilayer leaflets 2) different lipid composition of different cellular membrane systems 3) patchy distribution of proteins and Lipids e.g. lipid rafts

Question 24

What does the lipid bilayer consist of?

Answer 24

Two distinct leaflets that have a distinctly different lipid composition

Question 25

What happens when intact human RBC are treated with lipid-digesting phospholipase?

Answer 25

80% of the phosphatidyl-choline of the membrane is hydrolysed Only 20%: phosphatidylethanolamjne and less than 10: phosphatidylserine are attacked

Question 26

What does the outer leaflet have a high concentration and low concentration of?

Answer 26

High - phosphatidylcholine (PC) Low - PE and PS

Question 27

What does the endoplasmic reticulum have high levels of?

Answer 27

Phosphatidylcholine (PC)

Question 28

What if the intermediary between ER and PM?

Answer 28

Golgi complex

Question 29

What does the artificial bilayer consist of?

Answer 29

Phosphatidylcholine and sphingomyelin

Question 30

What was observed when studying artificial bilayer?

Answer 30

Cholesterol and sphingolipida tend to pack together to form micro domains that are more gelated and highly ordered

Question 31

Where does cholesterol-rich microdomain tend to float?

Answer 31

More fluid and disordered environment of the artificial bilayer

Question 32

What is lipid rafts?

Answer 32

Concentrate particular proteins thereby organising the membrane into functional compartments

Question 33

What does lipid fast provide?

Answer 33

Favourable local environment for cell surface receptors to interact with other membrane proteins that transmit signal from extracellular surface to cell interior

Question 34

Where is a GPI-anchored protein localised in?

Answer 34

Fat

Question 35

What does the inner leaflet raft lipid consist of?

Answer 35

Cholesterol and glycerol

Question 36

What are kinase involved in?

Answer 36

Cell signalling

Question 37

What is the best evidence for lipid rafts?

Answer 37

Simple, artificial model Membranes

Question 38

What are the methods for measuring mobility?

Answer 38

1) microscope 2) cell fusion 3) fluorescence recovery after photo bleaching (FRAP) 4) single particle trafficking

Question 39

Cell fusion

Answer 39

Technique where two different types of cells(two different species) can be fused to produce a new cell with a common cytoplasm and single continuous plasma membrane

Question 40

How was the effect of temperature on the diffusion of membrane proteins revealed?

Answer 40

Examining percentage of cells in which the proteins from two species have become intermixed after 49 Mins after fusion

Question 41

FRAP

Answer 41

A membrane protein can be labelled using a specific probe (fluorescent antibody) Labelled cells are placed under the microscope and irradiated by a sharply focused laser beam that bleaches the fluorescent molecules Leaves a circular spot on the surface of cell that is largely devoid of fluorescence

Question 42

What does the rate of fluorescence recovery provide?

Answer 42

Direct measure of the rate of diffusion of mobile molecules

Question 43

What is single-particle trafficking?

Answer 43

Label individual membrane protein molecules or Lipids and follow their movement by high-speed video microscopy

Question 44

What does computer analysis indicate?

Answer 44

Phospholipid diffuses freely within one compartment before it jumps the fence into neighbouring compartment

Question 45

What are the movement of membrane proteins?

Answer 45

A) some membrane proteins move randomly throughout the membrane B) some membrane proteins fail to move and are immobilised C) some proteins nice in a highly directed manner toward one party of cell or another D) some membrane are crowded with proteins, the random movement of one molecule can be impeded by its neighbour E) membrane underlying skeleton forms network of fences around portions of membrane, create compartment that restrict the distance an integral protein can travel F) movement of transmembrane protein through bilayer is slowed by the presence of extracellular material that can entangle the external portion of protein molecule