The Membrane Bilayer

Question 1

How much protein, lipid and carbohydrate does a membrane usually contain?

Answer 1

Protein = 60%
Lipid = 40%
Carbohydrate = 1-10%

Question 2

What percentage of the total weight of a membrane is water?

Answer 2

20%

Question 3

What is the name of a phospholipid based on?

Answer 3

It’s head group

Question 4

How long are the fatty acids chains usually in phospholipids?

Answer 4

C16 - C18

Question 5

What makes sphingomyelin different to the other phospholipids?

Answer 5

No glycerol backbone

Question 6

What are the 2 types of glycolipids?

Answer 6

Cerebrosides and gangliosides

Question 7

What is a cerebroside?

Answer 7

A glycolipid whose head group is a sugar monomer

Question 8

What is a ganglioside?

Answer 8

A glycolipid whose head group is a oligosaccharide.

Question 9

What are some of the functions of biological membranes?

Answer 9

Selectively permeable barrier, control of enclose environment, communication, recognition and signal generation.

Question 10

Do phospholipids more naturally form micelles or bilayers?

Answer 10

Bilayers

Question 11

What motions are available to phospholipids?

Answer 11

Flexion
Rotation
Lateral diffusion
Flip-flop (rare)

Question 12

How does cholesterol integrate itself into the membrane?

Answer 12

The cholesterol OH group forms hydrogen bonds with the phospholipid.

Question 13

How does cholesterol increase membrane fluidity?

Answer 13

Reduces phospholipid packing

Question 14

How does cholesterol decrease membrane fluidity?

Answer 14

Reduces phospholipid chain motion

Question 15

What functions of the membrane give us evidence for presence of proteins?

Answer 15

Facilitated diffusion
Ion gradients
Specificity of cell responses

Question 16

What are the biochemical methods of testing for proteins in the membrane?

Answer 16

Fractionation and electrophoresis

Freeze fracture

Question 17

What movements are available to proteins in the membrane?

Answer 17

Conformational changes
Rotation
Lateral diffusion

Question 18

What restricts the movement of proteins in the membrane?

Answer 18

Aggregates
Tethering
Interaction with other cells

Question 19

Where do you find more proteins in a membrane?

Answer 19

In cholesterol poor regions

Question 20

How do we remove peripheral proteins?

Answer 20

Changes in pH or ionic strength

Question 21

How do we remove integral proteins?

Answer 21

Use agents that compete for non-polar interactions (eg. Detergents)

Question 22

Approximately how many amino acids are needed to span a membrane?

Answer 22

18 - 22 amino acids

Question 23

Often TMDs are which shape?

Answer 23

Alpha helical

Question 24

What do hydropathy plots tell us?

Answer 24

The relative hydrophobicity or hydrophilicity of amino acids in the protein and then we can work out where those amino acids will reside. (Eg. Which ones are in the TMDs)

Question 25

Describe hereditary spherocytosis

Answer 25

Spectrin deficiency
RBCs become spherical
Leads to increased lysis therefore leads to anaemia
Must have frequent blood transfusions

Question 26

Describe hereditary elliptocytosis

Answer 26

Defect in spectrin
Unable to form properly
RBCs are elliptic
More prone to lysis therefore anaemia occurs

Question 27

What molecule is sphingomyelin based on and where is it found in the highest concentrations?

Answer 27

Sphingosine

Nervous tissue

Question 28

Briefly describe cholesterol

Answer 28

Steroid alcohol
4 fused hydrocarbon rings
Modulates fluidity of cell membranes
Very hydrophobic 
Synthesised by virtually all tissues in humans

Question 29

Give examples of hydrophobic molecules that can easily pass through the cell membrane

Answer 29

Oxygen (O2)
Nitrogen (N2)
Carbon dioxide
Benzene

Question 30

What is passive transport dependent on?

Answer 30

Permeability

Concentration gradient