M&R Session 1

Question 0

Membrane composition?

Answer 0

60% protein
40% lipid
1-10% carbohydrate

Question 1

5 main functions of biological membranes?

Answer 1

1. Selectively permeable barrier
2. Control chemical environment
3. Communication
4. Recognition
5. Signal generation

Question 2

Structure of phospholipids?

Answer 2

Glycerol
2 FA chains
Phosphate head group

Question 3

What are cerebrosides?

Answer 3

Glycolipids with sugar monomer heads

Question 4

What are gangliosides?

Answer 4

Glycolipids with oligosaccharide head groups

Question 5

What kind of molecules are membrane lipids?

Answer 5

Amphipathic

Question 6

Four methods of lipid mobility?

Answer 6

1. Intra-chain motion
2. Fast-axial rotation
3. Fast lateral diffusion
4. Flip-flop

Question 7

Three modes of permitted mobility of proteins in biological membranes?

Answer 7

1. Conformational change
2. Rotational
3. Lateral

Question 8

Restraints on protein mobility in membranes?

Answer 8

Flip flop too energetic
Aggregates - movement w/in membrane slower
Tethering - cannot physically move
Interaction w/other cells - adhesion proteins fixed
Lipid mediated effects - prefer cholesterol poor regions

Question 9

Evidence for membrane proteins?

Answer 9

Facilitated diffusion
Ion gradients
Specificity of cell responses
Membrane fracture

Question 10

Amphipathic molecule arrangement in water?

Answer 10

Micelle or bilayer

Question 11

How are liposomes formed?

Answer 11

Enclosure by lipid bilayer in aqueous media

Question 12

Structure of cholesterol?

Answer 12

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

Question 13

What is the function of cholesterol in the phospholipid bilayer?

Answer 13

Abolishes endothermic phase transition (reduces melting temperature)
Reduces phospholipid chain motion (reduces fluidity)

Question 14

How does cholesterol reduce fluidity in the CSM?

Answer 14

Beta-OH locks onto adjacent phospholipid - rigid ring obstructs packing

Question 15

Is the flexible tail motion of a phospholipid bilayer affected by cholesterol?

Answer 15

No

Question 16

What is the overall result of cholesterol on a phospholipid bilayer?

Answer 16

Homogenise properties to keep membrane constant over a greater range of temperatures

Question 17

Why is there no flip-flop of membrane proteins?

Answer 17

Hydrophilic structure too large to cross hydrophobic domain - too much energy and resultant disruption to ion gradients too great

Question 18

Classifying features of peripheral membrane proteins?

Answer 18

Bound to surface (can be washed off)
Electrostatic and H bond interactions
Removed by changes in pH/ionic strength

Question 19

What type of membrane protein prefers cholesterol-rich areas?

Answer 19

Transducers of protein-protein associates

Question 20

Features of integral membrane proteins?

Answer 20

Interact extensively w/hydrophobic domains

Only removed by non-polar interaction competitors (detergents/organic solvents)

Question 21

Typical length of transmembrane polypeptides?

Answer 21

18-22 a.a.

Question 22

Typical structure of transmembrane polypeptides?

Answer 22

Hydrophobic R groups

Alpha-helical transmembrane domains

Question 23

How do glycoproteins orientate?

Answer 23

Oligosaccharides outside
Disulphide bonds outside
Transmembrane helix inside
Sulphylhydryl groups inside

Question 24

Where are dolichol phosphate-linked p.p. attached to CSM?

Answer 24

On membrane lipids on extracellular side

Question 25

What causes FA of lipids to reinsert into the bilayer? | What is the effect?

Answer 25

Post-translational modification | Restricts protein movement

Question 26

Are peripheral protein associations extracellular or in the cytosol?

Answer 26

Both - Hah!

Question 27

Why is asymmetrical orientation of membrane proteins important?

Answer 27

Receptor needs recognition site towards extracellular space

Question 28

What is the structure of spectrin?

Answer 28

Alpha and beta subunits wind together --> antiparallel heterodimer Long, floppy, rod-like (tee hee) Heterotetramer formed by head-to-head association of 2 molecules

Question 29

Which molecules restrict lateral mobility of membrane proteins?

Answer 29

Ankyrin | Band 4.1

Question 30

Give two examples of haemolytic anaemias.

Answer 30

Hereditary spherocytosis | Hereditary elliptocytosis

Question 31

Give an overview of hereditary spherocytosis.

Answer 31

Relatively rare Spectrin decreased by 40-50% Erythrocytes round up and shear through narrow lumen RBCs less resistant to lysis --> easily fatiguable Tx: adapt lifestyle and blood transfusion

Question 32

Give a brief overview of hereditary elliptocytosis.

Answer 32

Defect in spectrin molecule Can't form heterotetramers --> no mesh Fragile, elliptoid cells

Question 33

What defines the orientation of a membrane protein?

Answer 33

Positioning of positively charged residues at N or C-terminal end of start-transfer sequence during protein synthesis

Question 34

How is a membrane protein oriented with C terminus into the ER lumen?

Answer 34

+ve residue at N terminus of start-transfer sequence

Question 35

What directs the N terminus of a membrane protein into the ER lumen?

Answer 35

+ve residue at C-terminal end of start-transfer sequence

Question 36

What is the function of the stop codon during membrane protein synthesis?

Answer 36

Clamp protein in the membrane

Question 37

What stabilises the partially folded growing p.p. in multiple transmembrane domain protein synthesis?

Answer 37

Lumenal binding proteins (related to heat-shock proteins)

Question 38

Give a one sentence description of how G-protein coupled receptors are formed.

Answer 38

Spanning domains made outside and inserted into the membrane

Question 39

Is protein orientation maintained during exocytosis?

Answer 39

Yes

Question 40

Describe the vesicle resulting from endocytosis.

Answer 40

Sealed inside-out vesicle with reversed protein orientation

Question 41

Describe the vesicle resulting from exocytosis.

Answer 41

Sealed right-side out vesicle

Question 42

What property do the precursory vesicles of both exocytosis and endocytosis share?

Answer 42

They are leaky before they become sealed