Membrane Bilayer and Proteins

Question 1

What are the functions of biological membranes? (5)

Answer 1

1. continuous, highly selective permeability barrier
2. controls the enclosed chemical environment
3. communication
4. recognition- signalling molecules (also inc adhesion proteins and immune surveillance)
5. signal generation in response to stimuli

Question 2

What are the approximate membrane composition dry weights?

Answer 2

40% lipid
60% protein
1-10% carbohydrates

Question 3

Membranes tend to be hydrated structures though. What does this mean?

Answer 3

20% of total weight is water

Question 4

Describe membrane lipids

Answer 4

they are amphipathic molecules (contain both a hydrophilic and hydrophobic moiety/ group)

Question 5

What is the generic shape of a phospholipid?

Answer 5

glycerol backbone
two fatty acid chains coming off the backbone
a phosphate attached to backbone and a head group attached to the phosphate

Question 6

What are properties of the phospholipids head groups?

Answer 6

they have a range of polar head groups

e.g choline, amines, amino acids, sugars - all of these are small molecules

Question 7

What are the properties of the phospholipids fatty acid chains?

Answer 7

length is between 14 and 24 carbons
carbon 16 and 18 are the most prevalent lengths
they are highly saturated
unless a cis double bond is introduced which produces a kink

Question 8

What are four phospholipid head groups?

Answer 8

choline
serine
ethanolamine
inositol

Question 9

What is sphingomyelin?

Answer 9

It is a phospholipid without a glycerol backbone and instead has a sphingosine backbone

Question 10

What are glycolipids?

Answer 10

replace the phosphocholine moiety with a sugar

they are sugar containing lipids

Question 11

What are the two types of glycolipids?

Answer 11

cerebrosides- head group sugar monomer

gangliosides- head group oligosaccharide (sugar multimers)

Question 12

Where and why are gangliosides important?

Answer 12

to function in central nervous system and also for the invasion of invading particles which use gangliosides to gain entry to the cell

Question 13

How is a lipid micelle formed?

Answer 13

Put an amphipathic liquid in water and suffocate it (shake it up into the water)

Question 14

Describe the lipid micelle

Answer 14

the hydrophilic head groups face outwards

the hydrophobic tails face inwards

Question 15

What are lipid micelles the basis of and why?

Answer 15

Washing up liquid

the fat on the plats can be dissolved in the hydrophobic part of the structure and stabilised by the hydrophilic groups which allows the fat to be washed down the sink

Question 16

Why are phospholipids unusual?

Answer 16

instead of forming a lipid micelle, when put into an aqueous environment they form lipid bilayers

Question 17

Which lipids are involved in biological membranes?

Answer 17

phospholipids
glycolipids
cholesterol

Question 18

How do phospholipids move?

Answer 18

by Brownian motion

Question 19

What are the four possible motions of phospholipids?

Answer 19

flexion
rotation
flip flop
lateral diffusion

Question 20

How is phospholipid packing reduced?

Answer 20

when unsaturated hydrocarbon chains have cis double bonds

Question 21

Why do you need unsaturated fat in your diet?

Answer 21

because further down the chain it can’t be made in our bodies