Session 1

Question 1

What is an amphipathic molecule?

Answer 1

One that contains hydrophobic and hydrophillic sections

Question 2

What is the cell membrane mostly made of?

Answer 2

Protein then lipids

Question 3

What are the main types of lipids in the membrane?

Answer 3

Phospholipids

Question 4

What is special about the phospholipid fatty chain?

Answer 4

It is unsaturated and in the cis form. This causes a kink in the chain so reduces phospholipid packing.

Question 5

What are the types of phospholipids?

Answer 5

Plasmalogens,
Spingomyelin
Glycoproteins

Question 6

What are the 2 types of Glycerol molecules?

Extra point - What is different about them?

Answer 6

Cerebrosides and Gangliosides

Extra point - Cerebrosides have head group sugar monomers. Gangliosides have head group sugars oligosaccharides.

Question 7

How much of the membrane lipids does Cholesterol make?

Answer 7

45%

Question 8

What are the 2 shapes amphiphatic molecules can form in water?

Answer 8

Miscelles and Bilayers

Question 9

What causes bilayer formation of phospholipids in water?

Answer 9

Van der Waals forces between the hydrophobic tails

Question 10

What stabilises the co operative shapes of phopsholipids in water?

Answer 10

The electrostatic and hydrogen bonds between the hydrophobic sections and interactions between hydrophillic groups and water.

Question 11

What are the ways a lipid molecule can move within a bilayer?

Answer 11

Intra chain motion
Fast axial rotation
Fast lateral diffusion (within the plane of the bilayer)
Flip Flop (From one half of the bilayer to the other on a one for one exchange basis)

Question 12

What is the functional evidence for membrane proteins?

Answer 12

Facilitated diffusion
Ion gradients
Specificity of cell responses

Question 13

What is the Biochemical evidence for membrane proteins?

Answer 13

Fractionation and gel electrophoresis of the membrane.

Freeze fracture.

Question 14

What is Freeze Fracture?

Answer 14

A technique where a frozen cell is broken at its weakest section (Usually plasma membrane) then the ice is removed and a slide is placed under the electron microscope.

Question 15

What are the ways a membrane protein can move?

Extra point - Why can’t they flip flop?

Answer 15

Conformational change
Rotation
Lateral
Extra point - They have large hydrophilic sections so too much energy is required for them to move through the hydrophobic section of the bilayer.

Question 16

What are the restrictions on protein’s mobility in a bilayer?

Answer 16

Lipid mediated effects. (Tethering)
Membrane proteins associations (Aggregations)
Association with extra membranous proteins (interaction with other cells)

Question 17

How are peripheral membrane proteins bound to the surface of membranes?
Extra point - How can they be removed?

Answer 17

By electrostatic and hydrogen bonds.

Extra point - By changes in pH or ionic strength.

Question 18

How are integral membrane proteins bound to the membrane?

Extra point - How can they be removed?

Answer 18

They interact with the hydrophobic region of the bilayer (So cannot be removed with pH or ionic manipulation)
Extra point - Can be removed using agents that compete for the non polar interactions (eg detergents)

Question 19

What is the difference between membrane protein synthesis and secretory protein synthesis?
Extra point - How does it achieve this?

Answer 19

Membrane proteins need to span the membrane of a vesicle instead of being contained in it.
Extra point - The addition of a stop transfer signal.

Question 20

What can a hydropathy plot be used for?

Answer 20

Can be used to see how many transmembrane regions a protein has.

Question 21

Why is membrane asymmetry important?

Answer 21

For function. eg a receptor needs to have its recognition site towards the extracellular space.

Question 22

What property of unsaturated fatty acid chains causes an increase in membrane fluidity?

Answer 22

The double bonds allow cis formation to cause a kink in the chain which reduces packing.

Question 23

How does Cholesterol help stabilise the plasma membrane?

Extra point - What does this remove?

Answer 23

Hydrogen bonding to the fatty acid chains.

Extra point - The endothermic phase transition (Where the molecules melt into a liquid.)

Question 24

Cholesterol increases membrane fluidity and decreases it at the same time. Why?

Answer 24

Cholesterol reduces the phospholipid packing (Increasing fluidity)
Cholesterol reduces phospholipid chain motion (decreases fluidity)

Question 25

What effects lateral diffusion of proteins through the membrane?

Answer 25

Size - Protein aggregation and interacgtion with other extracellular proteins/cytoskeleton.
Lipid mediated effects - proteins separate into fluid phase or cholesterol poor regions.

Question 26

What is the cytoskeleton made of?

Answer 26

Spectrin and Actin molecules attached to the membrane by adapter proteins (Ankyrin and Glycophorin)

Question 27

What does attachment of an integral membrane protein to the cytoskeleton restrict?

Answer 27

Lateral mobility of the membrane protein.

Question 28

Why is the erythrocyte skeleton so important?

Answer 28

Because without it the RBCs lose their shape and are lysed by shearing forces then cleared by the spleen.

Question 29

In what diseases is the erythrocyte skeleton destroyed?

Answer 29

Haemolytic anaemias.

Question 30

What is depleted in hereditary spherocytosis?

Answer 30

Spectrin levels (In common dominant form)

Question 31

How does hereditary spherocytosis lead to haemolytic anaemia?

Answer 31

Increases lysis of RBCs so they have a shorter lifespan. The bine marrow cannot compensate and haemolytic anaemia develops.

Question 32

What is the pathophysiology of hereditary elliptocytosis?

Answer 32

The spectrin molecules cannot form heterotetramers, results in fragile elliptoid cell shapes instead of biconcave which then lead to haemolytic anaemia.