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Question 1

What are the functions of biological membranes?

Answer 1

• highly selective permeabilty barrier
• Control of the enclosed chemical environment
• communication
• recognition-signalling molecules
  i. Adhesion proteins
  ii. Immune surveillance
• signal generation in response to stimuli (electrical, chemical)

Question 2

Dry weight general membrane composition

Answer 2

40% lipid
60% protein
1-10% carbohydrate

Question 3

Membranes are hydrated structures. What is the total weight of water in membranes?

Answer 3

20%

Question 4

What are the four different types of phospholipid head groups?

Answer 4

Choline, Serine, Ethanolamine and Inositol

Question 5

Name a phospholid with a special head group

Answer 5

Sphingomyelin

Question 6

Name two types of glycolipids

Answer 6

Cerebroside

Ganglioside

Question 7

What is the difference between cerebrosides and ganglioside?

Answer 7

C: Lipids with head group sugar monomer whereas G: Lipids with head group oligosaccharide (sugar multimers).

Question 8

Draw a lipid micelle

Answer 8

Image

Question 9

Image

Answer 9

Lipid micelle

Question 10

What is liposome?

Answer 10

Lipid bilayer around a cell

Question 11

Draw a lipid bilayer

Answer 11

Image

Question 12

What motions are possible with phospholipids?

Answer 12

Flexion, rotation, flip flop (rare) and lateral diffusion

Question 13

What influence does a cis double bond have in bilayer structure?

Answer 13

Reduces phospholipid packing so increases fluidity.

Question 14

Describe the structure of cholesterol

Answer 14

Polar head group on top of a rigid planar steriod structure with a non-polar hydrocarbon tail.

Image

Question 15

What’s the effect of cholesterol concentration on the endothermic phase transition of phospholipid bilayers?

Answer 15

As cholesterol concentration increases endothermic phase transition decreases.

Image

Question 16

Where does cholesterol insert and bind in the phospholipid bilayer?

Answer 16

Cholesterol inserts between the hydrophobic tails of phospholipids and the polar OH group of the cholesterol binds to the double bonded O of the ester group in the phospholipid.

Question 17

How does cholesterol restrict motion of phospholipid tails?

Answer 17

The upper region of the phospholid tail is aligned with the rigid steriod structure of cholesterol so it’s motion is restricted. However, the lower region of the phospholid tail is aligned with the non polar hydrocarbon tail of the cholesterol so its motion is unaffected.

Question 18

Explain the paradoxical effects of cholesterol in phospholipid bilayers

Answer 18

Cholestrol descrease fluidity of the bilayer by reducing phospholid chain motion but also increases fluidity of the bilayer by reducing phospholid packing.

Question 19

What is the functional evidence for proteins in membranes?

Answer 19

• Facilitated diffusion
• Ion gradients
• specificity of cell responses

Question 20

What are the biochemical evidence for protein s in membranes?

Answer 20

• Membrane fractionation + gel electrophoresis

- Freeze Fracture

Question 21

What can be used to make the membrane fractionation+ gel electrophoresis?

Answer 21

SDS-Polyacrylamide gel electrophoresis (SDS-PAGE)

Question 22

Describe how freeze fracture works

Answer 22

Cell is frozen in water and then fractured with a knife to produce an E fracture face and a P fracture face.

Question 23

What are the three modes of motion permitted for proteins?

Answer 23

Conformational change
Rotational
Lateral

Question 24

What mode of action is not permitted for proteins? And why?

Answer 24

Flip-flop because it is not thermodynamically favourable.

Question 25

What are the three ways in which membrane proteins’ mobility can be restricted?

Answer 25

Aggregates
Tethering
Interaction with other cells

Question 26

How does lipid mediated effects restrain mobility?

Answer 26

Proteins tend to separate out into the fluid phase or cholesterol poor regions.

Question 27

What are the two types of membrane proteins?

Answer 27

Peripheral and integral

Question 28

What are the differences between peripheral and integral membranes proteins?

Answer 28

Peripheral:

• bound to surface
• electrostatic and hydrogen bond interactions
• Removed by changes in pH or in ionic strength

Integral:

• Interact extensively with hydrophobic domains of the lipid bilayer
• Cannot be removed by manipulation of pH or ionic strength
• Are removed by agents which compete for non-polar interactions

Question 29

What agents will compete with integrals for non-polar interactions?

Answer 29

Detergents and organic solvents

Question 30

The lipid mosaic model of membrane structure is also known as what?

Answer 30

Singer-Nicholson model

Image

Question 31

What are two key features about the structure of transmembrane polypeptide?

Answer 31

• R groups of amino acid residues in transmembrane domains are largely hydrophobic
• transmembrane domains are often alpha helical.

Question 32

How is the erythrocyte’s shape maintained?

Answer 32

The erythrocyte’s shape is held together by the cytoskeleton.

Question 33

How is spectrin lattice anchored? (detailed)

Answer 33

Band 3 and Glycophorin A (transmembrane proteins) anchor spectrin lattice adhered through ankyrin and Band 4.1 which are attachment proteins.

Image

Question 34

How is the spectrin lattice anchored?(general)

Answer 34

transmembrane proteins anchor spectrin lattice adhered through attachment proteins.

Image

Question 35

Examples of haemolytic anaemias

Answer 35

Hereditary Spherocytosis

Hereditary Elliptocytosis

Question 36

What is hereditary spherocytosis?

Answer 36

Spectrin is depleted by 40-50% causing erythrocytes to round up. This means less resistance to lysis and clearance by spleen.

Question 37

What is hereditary Elliptocytosis?

Answer 37

Defect in spectrin molecule where there is no hereterotetramer formation so fragile elliptoid cells (look like rugby balls)