Lecture 11: The Structure, Organisation and Properties of Membranes

Question 1

What are the functions of membranes ?

Answer 1

1. Enclosure
2. Transport
3. Signals
4. Enzyme catalysis
5. Interactions with other cells
6. Anchoring the cytoskeletons

Question 2

What is enclosure ?

Answer 2

A surrounding barrier function

Question 3

What is transport ?

Answer 3

Membranes represent permeability barriers

Question 4

What is signals?

Answer 4

Reception of extracellular signals and trasfer to interior

Question 5

What are membranes composed of ?

Answer 5

Largely proteins and lipids some carbohydrates

Question 6

What is the major phospholipid of animal cells ?

Answer 6

Phosphocholine

Question 7

What is the major phospholipid in bacteria ?

Answer 7

Phosphoethanolamine

Question 8

What is not present in mitochodrial or bacterial membranes ?

Answer 8

Shingomyeline

Question 9

What is a membrane ?

Answer 9

A continuous bilayer of amphipathic lipids

Question 10

What do fluidity membranes exist in ?

Answer 10

Liquid crysatl state

Question 11

What are membranes characterised by ?

Answer 11

An asymetry in lipid and protein composition

Question 12

Why do bacteria not lyse when put in distilled water ?

Answer 12

Rigid exoskeleton

Question 13

What did Gorter and Grendal conclude ?

Answer 13

Lipids must be arranged as a bilayer

Question 14

What did the Danielli and Davson model conclude ?

Answer 14

Polar head groups interacted with protein layers

Question 15

What were the problems with Danielli and Davson model ?

Answer 15

1. Assumed membranes had the same structure
2. The arrangement of proteins

Question 16

What is the idea behind the fluid mosaic model ?

Answer 16

Proteins can be embedded in bilayer, and can sometimes protrude and be associated with one surface or leaflet

Question 17

What did studies of tyrpsin on membrane show ?

Answer 17

Proteins distributed on both sides of the membrane

Question 18

What is different when proteases has access to both sides of the membrane ?

Answer 18

The pattern of proteins susceptible of digestion

Question 19

Where are proteins mobile ?

Answer 19

Surface bilayer

Question 20

What does FRAP stand for ?

Answer 20

Fluorescence recovery andfter photobleeching

Question 21

Where is ptd-inositol found ?

Answer 21

Inner leaflet

Question 22

Where are glycolipids found ?

Answer 22

Outer leaflet

Question 23

Where are lipids symetrically distributed ?

Answer 23

Endoplasmic reticulum

Question 24

Where are lipids asymetrically distributed ?

Answer 24

Golgi, endosomal and plasma membrane of eukaryptoes

Question 25

How are lipids distributed ?

Answer 25

1. Biophysical properties allow spontaneous flipping of polar headgrop through the hydrophobic membrane interior
2. Transporters that drive active lipid translocation across bilayer

Question 26

What are the three types of ATP dependent transporters ?

Answer 26

1. Flippase
2. Floppase
3. Scramblase

Question 27

What do flippase and floppase do ?

Answer 27

Generate and maintain lipid asymetry

Question 28

What does scramblase do ?

Answer 28

Collapses asymetry

Question 29

What are the factors that affect membrane fluidity ?

Answer 29

1. Temperature
2. Long chain fatty acids
3. Protein content
4. External facotrs