Lecture 2- The Cell Membrane

Question 1

the cell membrane

Answer 1

provide a highly selective but permeable barrier around the cell

Question 2

cell membrane role

Answer 2

• communication
• recognition of signalling molecules
• signal generation in response to stimuli

Question 3

membrane composition (dry weight) of lipids

Answer 3

40%

Question 4

membrane composition (dry weight) of proteins

Answer 4

60%

Question 5

membrane composition (dry weight) of CHO

Answer 5

1-10%

Question 6

cell membranes are hydrated how much of total mass

Answer 6

20%

Question 7

what does amphiphatic mean

Answer 7

contain both hydrophilic and hydrophobic moiety

Question 8

cell membrane forms a

Answer 8

lipid bilayer

Question 9

lipid bilayer made out of

Answer 9

phospholipids

Question 10

phospholipids are

Answer 10

amphiphatic

Question 11

hydrophobic

Answer 11

fatty acid tails point inwards

Question 12

phosphate head

Answer 12

is the negatively-charged polar head, which is hydrophilic.

Question 13

structure of a fatty acid

Answer 13

one phosphate group attached to two fatty acid chains by glycerol

Question 14

length of fatty acid chain

Answer 14

between C14-24

Question 15

most prevalent fatty acid length

Answer 15

C16-18

Question 16

what introduces a kink in fatty acid chain

Answer 16

cis double bone

Question 17

head groups

Answer 17

rage of polar head goops e..g choline, Amines, amino acids and sugars

Question 18

what are glycolipids

Answer 18

sugar containing lipids

Question 19

examples of glycoplipids in cell membrane

Answer 19

• cerebrosides

- gangliosides

Question 20

cerebrosides

Answer 20

simple (single sugar monomer) glycolipids attached to fatty acid tail

Question 21

gangliosides

Answer 21

oligosaccharides (sugar multimers) attached to fatty acid tail

Question 22

how can Cis double bond influence bilayer sturcture

Answer 22

introduces Kink

- in an unsaturated chain (e.g. with CIS) the kink reduced phospholipid packing

Question 23

saturated phospholipid hydrocarbon chains

Answer 23

straight chained- more highly packed- less fluid

Question 24

if you drop hydrophic molecules in water what would form

Answer 24

micelle

Question 25

if you put phospholipid into water it doesn’t form micelles it forms

Answer 25

the lipid bilayer- sheets

Question 26

liposomes

Answer 26

have phospholipid bilayer- amphiphatic- good way of delivering drugs- fusing with the membrane

Question 27

phospholipids are dynamic- how can they move

Answer 27

• flexion
• rotation
• lateral diffusion
• flip flop

Question 28

why is flip flopping rare for phospholipids

Answer 28

needs lots of energy- dynamically unfavouravle

Question 29

cholesterol makes up how much of the mmebrane

Answer 29

45%

Question 30

how many cholesterol in terms of phospholipids

Answer 30

every phospholipid will be attached to a cholesterol in some way

Question 31

structure of cholesterol

Answer 31

• Polar head group (amphiphatic)
• Rigid planar steroid ring structure
• Non- polar hydrocarbon tail
• Leaves hydroxyl group on the outside
• Chunky solid molecule

Question 32

function of cholesterol

Answer 32

Stabilises the membrane- keeping it fluid, but also stopping it from freezing

Question 33

cholesterol abolishes

Answer 33

Cholesterol abolishes endothermic phase transition of phospholipid bilayers

Question 34

example of how cholesterol works

Answer 34

1. Stabilises the membrane- keeping it fluid
2. As you raise the temperature of a pure phospholipid- the cholesterol will take in a huge amount of energy
3. Adding cholesterol reduces rate of heat flow
4. Stops membrane melting as temp increases

Question 35

how is cholesterol inserted in the mebranr

Answer 35

when its hydroxyl group forms hydrogen bonds with the carbonyl oxygen of the fatty acid side chain- positioning cholesterol next to phospholipids.

Question 36

putting rigid groups like cholesterol next to phospholipids

Answer 36

reduces its mobility- reducing fluidity of the membrane- doesn’t melt when heated

Question 37

cholesterol also reduces,,

Answer 37

phospholipid packing- increasing fluidity