The Cell Membrane

Question 1

What are the general functions of cell membranes?

Answer 1

Continuous, selective permeability barrier
Control of enclosed chemical environment Communication
Recognition signalling molecules
Signal generation in response to stimuli

Question 2

Examples of signalling molecules?

Answer 2

Adhesion protein

Immune surveillance

Question 3

What is the composition of membranes in dry weight?

Answer 3

40% lipid
60% protein
1 to 10% carbohydrates

Question 4

What are the ranges of fatty acid chains?

Answer 4

C14-C24 and C16-C18

Question 5

Examples of phospholipid head groups?

Answer 5

Choline
Define
Ethanolamine
Inositol

Question 6

What is a sphingomyelin?

Answer 6

(Sphingolipids) it’s the only other phospholipid with a phosphate in the membrane.

Question 7

What is a liposome? Their use?

Answer 7

An enclosed structure.

Delivery of drugs

Question 8

What are cerebrosides and gangliosides?

Answer 8

Cerebrosides- head group sugar monomer Gangliosides- head group oligosaccharide (sugar multimers)

Question 9

What are the different types of phospholipid motion?

Answer 9

Flexion
Rotation
Lateral diffusion
Flip-flops

Question 10

What are the influences of cis double bonds in the bilayer structure?

Answer 10

Unsaturated hydrocarbons chains with sis double bonds reduce phospholipid packing increasing the fluidity

Question 11

What is the structure of cholesterol?

Answer 11

Polar had a group, rigid planar steroid ring structure. Non polar (flexible) hydrocarbon tail. Hydroxyl head group

Question 12

What is the significance of the hydrogen bond between the

Answer 12

Reduces mobility and motion therefore reducing the fluidity

Question 13

What is the paradoxical effect of cholesterol?

Answer 13

Reduced phospholipid chain motion reduces fluidity.

Reduced phospholipid packing increases fluidity

Question 14

What are lipid rafts?

Answer 14

Dynamic cholesterol rich structures comprised of sphingolipids with saturated fatty acid chains and tightly integrated cholesterol

Question 15

What is the function of lipid rafts?

Answer 15

Signalling scaffolds which allows dimerisation of signalling pathways

Question 16

What are the two types of evidence for proteins in membranes?

Answer 16

Functional- facilitated diffusion

Biochemical- freeze fracture and gel electrophoresis

Question 17

What is freeze fracture and two faces?

Answer 17

Fracturing a crystal with a knife, between two membrane lamella. P fracture face and E fracture face.

Question 18

What is SDS?

Answer 18

A detergent that coats all proteins with a negative charge so they move in the same direction during a gel electrophoresis.

Question 19

What are the three modes of mobility of proteins in the bilayer?

Answer 19

Confirmational change
Rotational
Lateral

Question 20

Why can’t proteins flip-flop?

Answer 20

The amount of hydrophilic structure that is exposed to the aqueous environment is too big and too energetically unfavourable to flip across the membrane

Question 21

What are the restrictions of proteins in the bilayer?

Answer 21

Membrane protein associations
Association with extramembranous proteins
Lipid mediated effects

Question 22

What are the two main membrane proteins and their features?

Answer 22

Peripheral they have electrostatic and hydrogen bonds interactions, removed by changes in pH or in ionic strength

Integral they interact extensively with hydrophobic domains of the bilayer, removed by agents that compete for nonpolar interactions

Question 23

What are transmembrane polypeptide composed of?

Answer 23

Small, hydrophobic, polar and charged amino acids R groups. Alpha helical domains.

Question 24

What is a hydropathy plot?

Answer 24

To check for membrane proteins

Question 25

What does the membrane protein topology look at?

Answer 25

Orientation in the bilayer

Question 26

Purpose of an SDS page of erythrocyte membrane?

Answer 26

To distinguish between peripheral and integral proteins

Question 27

What are the key features of the erythrocytes cytoskeleton?

Answer 27

Transmembrane protein anchors

Spectrin lattice adhered through attachment proteins

Question 28

What are the two types of haemolytic anaemia and their features?

Answer 28

Hereditary spherocytosis- spectrin depleted by 40 to 50% so less resistance to lysis

Hereditary elliptocytosis- defect in spectrin so can’t form heterotetramers