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Flashcards in MR S1 Deck (29):
0

What are the functions of membranes?

Selectively permeable barrier
Control of the enclosed chemical environment
Communication
Recognition
Signal generation in response to stimuli

1

What is the general composition of a membrane?

It varies between different membranes but the dry weight proportions are:
~40% lipid
~60% protein
~10% carbohydrate

2

In a hydrated membrane, what proportion of the weight is water?

~20%

3

What does amphipathic mean?

Molecule contains both hydrophobic and hydrophilic areas.

4

What is the structure of a phospholipid?

A glycerol molecule with two fatty acid side chains and a phosphate head

5

What effect would a double bond in a fatty acid side chain have?

The chain would have a kink

6

Describe the head chain of a phospholipid molecule

The head chain begins with a phosphate group which can have a variety of groups attached to it, for example:
Choline
Amine
Amino acid
Sugar

7

Describe the side chains of a phospholipid molecule

Fatty acid chain length can be between C14 and C24
Most common chain lengths are C16 and C18
Cis double bond creates a kink

8

What is a glycolipid?

Almost the same as a phospholipid, except the phosphate group is replaced with a sugar

9

What are the types of glycolipid?

Cerebrosides
Gangliosides

10

What is a cerebroside?

A glycolipid membrane molecule where the head group is a sugar monomer

11

What is a ganglioside?

A glycolipid membrane molecule where the head group is an oligosaccharide

12

How can individual phospholipid molecules move around the membrane?

Flip-flop
Lateral diffusion
Flexion
Rotation

13

What is the effect on the membrane as a whole of more cis double bonds in phospholipids?

Increased space between molecules/reduced packing

14

Describe the structure of cholesterol

Polar head group
Rigid planar steroid ring structure
Non polar hydrocarbon tail

15

What is the effect of cholesterol in membranes?

Maintains membrane fluidity in cold temperatures by preventing phospholipids from clumping together
Maintains membrane integrity and rigidity at higher temperatures by interacting with the side chains of phospholipids

16

Give an example of a phospholipid

Phosphtidylcholine

17

How can membrane proteins move around a membrane?

Lateral diffusion
Rotation
Conformational change

NO FLIP FLOP

18

What are the two types of membrane protein?

Integral - deeply embedded in the membrane
Peripheral - associated with the surface of the membrane

19

Describe peripheral membrane proteins

Only bound to the surface of the membrane by electrostatic or hydrogen bond interactions
May be easily removed by changes in pH or ionic strength

20

Describe intrinsic membrane proteins

Interact extensively with the lipid binding area of the phospholipid bilayer
Cannot be removed by pH or ionic manipulation, only by agents which compete for lipid interactions eg detergents

21

Why is asymmetrical orientation of proteins important?

A protein which interacts with the extra cellular environment would need to be correctly orientated in order to perform it's purpose eg an insulin receptor would need to have its insulin binding site on the extracellular side of the membrane

22

What is the evidence for proteins in membranes?

Functional:
Ion gradients
Facilitated diffusion
Specificity of cell response

Biochemical:
Freeze fracture
Membrane fractionation
Gel electrophoresis

23

What are some restraints on membrane protein mobility?

Lipid mediated effects eg proteins tend to separate out in cholesterol poor regions
Membrane protein associations
Association with extra membranous proteins eg cytoskeleton

24

What types of amino acids are likely to be in a transmembranous domain of a protein?

HYDROPHOBIC
Small
Uncharged

25

What are haemolytic anaemias? Give examples.

Diseases where there is reduced oxygen carried in the blood due to increased breakdown of red blood cells
Can have many causes eg hereditary spherocytosis

26

Describe hereditary spherocytosis

Spectrin depleted by 40-50%
Erythrocytes round up
Less resistant to haemolysis
Cleared up by the spleen
Reduced erythrocyte lifespan
Inability of bone marrow to adequately compensate causes haemolytic anaemia

27

Describe hereditary elliptocytosis

Defective spectrin formed
Unable to form stable heterotetramers
Fragile elliptoid cells
Reduced cell lifespan
Increased haemolysis
Bone marrow unable to adequately compensate
Anaemia

28

What is passive transport reliant on?

Membrane permeability
Concentration gradient