Membranes and Receptors

Question 0

Define amphipathic

Answer 0

Contains both hydrophobic and hydrophilic moieties

Question 1

What are the main kinds of lipids in plasma membranes?

Answer 1

Phospholipids
Glycolipids
Cholesterol

Question 2

Describe a phospholipid

And the range of head groups it may have

Answer 2

Glycerol backbone
Two fatty acid tails
Phosphate
Polar head groups could be choline, amines, amino acids and sugars

Question 3

What to cis double bonds do in phospholipids?

Answer 3

They reduce the packing between adjacent phospholipids

Question 4

Describe plasmalogens and give an example

LOOK OVER AGAIN AND EDIT

Answer 4

Non classical phospholipids such as sphingomyelin

Question 5

What is the difference between cerebrosides and gangliosides?

Answer 5

Both are glycolipids
Cerebrosides: head group is a sugar monomer
Gangliosides: head group is an oligosaccharide

Question 6

What are some general functions of membranes?

Answer 6

Barrier: continuous and highly selective
Control of enclosed chemical environment
Communication: ECF/ICF
Recognition: signalling molecules, adhesion, immune surveillance
Signal generation in response to stimuli

Question 7

What is the composition of a membrane?

Percentages dry weight

Answer 7

40% lipid
60% protein
1-10% carbohydrate
Water when hydrated 20% total weight

Question 8

What sort of movement can lipids do in bilayers?

Answer 8

Intrachain motion: cis formation increases fluidity
Fast axial rotation
Fast lateral diffusion
Flip flop - rare

Question 9

What are some functions of membrane proteins?

Answer 9

Enzymes
Transporters
Pumps
Ion channels
Receptors
Energy transducers

Question 10

Give evidence for proteins in membranes

Functional and biochemical

Answer 10

Functional: facilitated diffusion, ion gradients, specificity of cell responses
Biochemical: membrane fractionation, freeze fracture

Question 11

What sorts of protein mobility exist in bilayers?

Answer 11

Conformational change
Rotational
Lateral
NO FLIP FLOP: hydrophilic through hydrophobic region not energetically favourable

Question 12

What restrains protein mobility in a bilayer?

Answer 12

Membrane protein associations make movement sluggish
Proteins prefer cholesterol poor regions, fluid phase
Tethering to the cytoskeleton, other cells, basement membrane, peripheral proteins

Question 13

What is a peripheral protein?

Answer 13

Associated with the surface
Bound by electrostatic/H bond interactions
Remove with changes in pH or ionic strength

Question 14

What is an integral protein?

Answer 14

Interacts extensively with hydrophobic regions of the lipid bilayer
Can not remove by changing pH or ionic strength
Can remove with detergents or organic solvents which compete for non polar interactions
Hydrophobic R group residues mainly, alpha helical
1 or many hydrophobic domains

Question 15

Why is membrane asymmetry important?

Answer 15

Important for function
Receptors for hydrophobic extracellular messenger molecules
Needs to face ECF

Question 16

Describe how secreted proteins are synthesised

ESA1

Answer 16

Free ribosome
Hydrophobic N terminal sequence
Binds SRP, stops protein synthesis
GTP SRP binds to SRP receptors on the ER
SRP dissociates, protein synthesis continues
Protein into ER pore via PTC
Signal cleaved and the ribosome is recycled

Question 17

Describe membrane protein biosynthesis

Answer 17

Ribosomes start synthesising, hydrophobic N terminal sequence first
Binds SRP, stops synthesis and binds the SRP receptor, releases SRP
Continues protein synthesis, PTC interacts with signal, further synthesis through the ER
Ribosome is anchored to the pore, hydrophobic a helical area translated
Release of protein and ribosome from PTC, biosynthesis continues in the cytoplasm

Question 18

What does a hydropathy plot show?

Answer 18

The number of transmembrane domains in an integral membrane protein

Question 19

How is a membrane protein orientated?

GO OVER WITH MMF NOTES

Answer 19

Positive residues at the C end, N into the lumen
Positive residues at the N end, C into the lumen
Delivered to the membrane by the fusing of vesicles, same orientation as in ER

Question 20

Shat is the effect of unsaturated fatty acids in a membrane?

Answer 20

Cis double bond
Kink in the chain
Can not pack as tightly
More fluid

Question 21

Describe the structure of cholesterol

Answer 21

Polar OH head
Rigid steroid ring structure
Non polar hydrocarbon tail

Question 22

How does cholesterol increase fluidity?

Answer 22

Reduces the packing of phospholipids

Stops crystalline structure at low temperatures

Question 23

How does cholesterol reduce membrane fluidity?

Answer 23

Reduces chain motion on phospholipids
Rigid sterol structure
Reduces motion at high temps

Question 24

Describe erythrocyte membranes and how they are broken down

Answer 24

Over 10 major proteins, most released by changing pH or ionic strength, peripheral, cytosolic
Band 3 and 7 only removed by detergents, so are integral

Question 25

What is the importance of the cytoskeleton in RBCs?

Answer 25

Without it the RBCs round up
Lysed by shearing forces in the capillary bed
Cleared by the spleen, haemolytic anaemias

Question 26

What is hereditary spherocytosis?

Answer 26

Mutation in the spectrin allele, depletes it by 40-50%
Also can be mutated cytoskeletal elements, dysfunctional binding sites
RBCs round up, increased cell lysis
Bone marrow can not compensate
Haemolytic anaemia

Question 27

What is hereditary elliptocytosis?

Answer 27

Common defect in spectrin molecule
Can not form stable heterotetramers
Fragile elliptoid cells
Haemolytic anaemia

Question 28

What is the function of the RBC cytoskeleton?

Answer 28

Restricts laral mobility of integral membrane proteins

Also gives the cell flexibility, important to get through capillaries

Question 29

What is the main make up of the RBC cytoskeleton?

FINISH WITH LAST SESSION 1 page

Answer 29

Network of spectrin and actin

Adducin cross links spectrin