Membranes and Receptors

Question 1

What are the 5 general functions of biological membranes?

Answer 1

1) Highly selective permeability barrier
2) Control of enclosed environment
3) Communication
4) Recognition
5) Signal generation in response to stimuli

Question 2

What are the dry composition percentages of a biological membrane?

Answer 2

Lipid 40%
Protein 60%
Carbs 1-10%

Question 3

What percentage of the mass of a hydrated membrane does water contribute?

Answer 3

Water 20%

Question 4

Membrane lipids are amphipathic molecules. What is an amphipathic molecule?

Answer 4

A molecule that contains both hydrophilic and hydrophobic moieties.

Question 5

What type of lipids are predominant in a biological membrane?

Answer 5

Phospholipids

Question 6

What are the 4 main parts of a general phospholipid?

Answer 6

1) Head group
2 Phosphate
3) Glycerol
4) 2 fatty acid chains

Question 7

What is the head group on a phospholipid?

Answer 7

Range of polar molecules such as cholines, amines, sugars and amino acids

Question 8

What is sphingomyelin?

Answer 8

The only phospholipid not based on glycerol.

Question 9

What are the 2 types of glycolipid?

Answer 9

1) Cerebrosides: head group is a sugar monomer.

2) Gangliosides: head group is an oligosaccharide.

Question 10

What forces drive the spontaneous formation of a bilayer when phospholipids and glycolipids are in water?

Answer 10

Van der Walls attractive forces between hydrophobic tails.

Question 11

How is the bilayer structure stabilised in the hydrophilic region?

Answer 11

Non covalent forces ( ionic bonds and H bonds) between hydrophilic moieties.
Interactions between hydrophilic groups and water.

Question 12

What are the 4 dynamics of mobility a lipid bilayer can undergo?

Answer 12

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

Question 13

How do unsaturated double bonds in fatty acid chains increase membrane fluidity?

Answer 13

Double bonds disrupt hexagonal packing of phopholipids.

Question 14

What is the role of cholesterol?

Answer 14

To stabilise the plasma membrane.

Abolishes endothermic phase transition of phospholipid bilayers.

Question 15

At high temperatures, how does cholesterol reduce membrane fluidity?

Answer 15

It reduces phospholipid chain motion by using its rigid sterol ring.

Question 16

How does cholesterol increase membrane fluidity at low temperatures?

Answer 16

It reduces phospholipid packing.

Question 17

What are the 3 dynamics of mobility of proteins in the bilayer?

Answer 17

1) Conformational change
2) Rotation
3) Lateral diffusion

Question 18

What are the 2 types of evidence for protein existing in membranes?

Answer 18

1) Functional evidence

2) Biochemical evidence

Question 19

What are the 2 main types of membrane proteins?

Answer 19

1) Peripheral proteins

2) Integral proteins

Question 20

How can peripheral proteins be removed?

Answer 20

By changes in ph or ionic strength, eg; salt wash

Question 21

How can integral proteins be removed?

Answer 21

Using agents that compete for non polar interactions. Detergents and organic solvents.

Question 22

What does a hydropathy plot check for?

Answer 22

Multiple spanning transmembrane proteins.

Question 23

Describe the structure of amino acids in the transmembrane domain?

Answer 23

R group residues are small or hydrophobic.

Alpha helical structure.

Question 24

What are the 2 main molecules of a erythrocyte cytoskeleton?

Answer 24

Spectrin and actin molecules.

Question 25

How is spectrin-actin network attached to the cytoplasmic face of a membrane?

Answer 25

By adapter proteins: ankyrin and band 4.1.
Ankyrin—– band 3
Band 4.1——– glycophorin A

Question 26

Why is the erythrocyte skeleton important to the function of an erythrocyte?

Answer 26

Maintains deformability necessary for erythrocytes to pass through capillary beds without lysis.

Question 27

What are the 2 haemolytic anaemias?

Answer 27

1) Hereditary spherocytosis

2) Hereditary elliptocytosis

Question 28

What causes hereditary spherocytosis?

Answer 28

Spectrin is depleted by 40-50%, so erythrocytes round up and are more prone to lysis and are then cleared by the spleen. So erythrocytes have a reduced life span.

Question 29

What causes hereditary elliptocytosis?

Answer 29

Defect in spectrin molecule, so erythrocytes unable to form heterotetramers. Creates fragile elliptoid cells.