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Flashcards in MR 1 The Lipid Bilayer Deck (33):
0

What is an amphipathic molecule

One containing both hydrophilic and hydrophobic moieties

1

What is the general membrane composition?

40% lipid
60% protein
1-10% carbohydrate
20% water (membrane hydrated)

2

What molecules can be phospholipid head groups?

Choline, amines, amino acids, sugars

3

How long are the most common fatty acid chains?

C16 and c18

4

What formation are double bonds in fatty acid chains?

Cis

5

What do the double bonds in fatty acid chains do?

Introduce a kink in the chain decreasing phospholipid packing

6

What is a plasmalogen?

Non classical phospholipid e.g sphingomyelin

7

Why is sphingomyelin special?

Only phospholipid not based on glycerol. In membrane resembles other phospholipids

8

What is a glycolipid?

Sugar containing lipid

9

Define cerebroside and ganglioside

Cerebroside head group is a sugar monomer
Ganglioside head group is a sugar oligosaccharide

10

What % of membrane lipid does cholesterol make up?

45%

11

What two structures can amphipathic molecules form in water?

Micelles and bilayers

12

What drives spontaneous bilayer formation in water?

Van der waals between hydrophobic tails

13

What stabilises the cooperative structure of bilayers?

Non covalent forces; electrostatic and h-bonding between hydrophilic moieties and interactions between hydrophilic groups and water

14

In what ways can lipids move in bilayers?

Intra-chain motion: kink formation in fatty acyl chains
Fast axial rotation
Fast lateral diffusion within plane of bilayer
Flip-flop- movement from one half of bilayer to other on one for one exchange basis(rare)

15

Name the modes of motion of membrane proteins

Conformational change
Rotational
Lateral
NO FLIP FLOP

16

Why don't membrane proteins flip flop?

They have large hydrophilic moieties and large amounts of energy would be required for them to pass through the hydrophobic region of the bilayer

17

What restricts mobility of membrane proteins?

Lipid mediated effects- proteins spread out into fluid phase or cholesterol poor regions
Membrane protein associations
Association with extramembranous (peripheral) proteins e.g cytoskeleton

18

What are peripheral membrane proteins and how are they removed?

Bound to surface by electrostatic and hydrogen bonds (includes disulphide interactions)
Can be removed by changes in pH or ionic strength

19

What are integral membrane proteins and how are they removed?

Interact extensively with hydrophobic regions of bilayer.
Cannot be removed by changes in pH or ionic strength
Removed by detergents and organic solvents that compete for the non-polar interactions in the bilayer

20

How are membrane proteins translated so that they span the membrane of vesicles?

Using a stop transfer signal that is highly hydrophobic and remains in the ER so that the rest of the protein is translated outside of the ER in the cytoplasm

21

How long is the stop transfer signal?

18-20AAs which is the distance to span a phospholipid bilayer

22

What usually immediately follows a stop transfer signal?

A few basic (+ve) residues

23

What are hydropathy plots used for?

To see how many transmembrane regions a protein has

24

Why is asymmetrical orientation of proteins in membranes important?

Receptors for hydrophilic extracellular messengers like insulin must have recognition site facing towards extracellular space

25

How do fatty acids affect membrane fluidity?

Double bonds in chain reduce phospholipid packing increasing fluidity

26

How does cholesterol affect membrane fluidity?

Stabilises plasma membrane by H bonding to fatty acid chains
Abolishes endothermic phase transition of phospholipid bilayers
Reduces phospholipid packing, increasing fluidity
Reduces phospholipid chain motion decreasing fluidity

27

Explain the fluid mosaic model

Fluid- due to hydrophobic integral components such as lipids that move laterally throughout the membrane like a fluid

28

How is the shape of erythrocytes held?

Cytoskeleton of spectrin and actin

29

What proteins in the cytoskeleton are peripheral?

Actin
Spectrin
Ankyrin
Band 4.1
Adducin

30

Which erythrocyte cytoskeleton proteins are integral?

Band 3
Glycophorin A

31

What causes hereditary spherocytosis?

In dominant form spectrin is depleted by 40-50% so cells round up and lysis increases as RBCs have reduced lifespan

32

What causes hereditary Elliptocytosis?

Spectrin molecules unable to form heterotetramers giving fragile elliptoid cells leading to haemolytic anaemia