MCB L2

Question 1

State the function of plasma membranes

Answer 1

Enclose cell
Allows essential difference between cytosol + external environment
Impermeable - allows controlled access to inside cell

Question 2

State the function of ion gradients across membranes

Answer 2

Synthesis of ATP
Transport of selected solutes
Transmission of electrical impulses

Question 3

Descibe the structure of the cell membrane

Answer 3

Phospholipids
Proteins
(50:50)

Hydrophillic heads face outwards, hydrophobic tails face inwards

Creates a double bilayer - bimolecualr leaflet

Cell membranes are plastic + deformable + mobile

Fluid dynamic structure - lipid molecules move freely about the plane - rarely flip

Question 4

Describe the function of proteins in cell membranes

Answer 4

Form structural links with cytoskeleton - cytoskelton anchors components of cell membrane and keeps membrane rigid

Question 5

Describe the structure of phospholipids

Answer 5

Phosphate head - choline group linked to glycerol group via phosphate group

TWO hydrocarbon hydrophobic fatty acid tails
One tail = fully saturated (straight) One tail = unsaturated (1/ more cis double bond, giving it a kinked profile)

Question 6

State the structural significance of one of the hydrocarbon fatty acid chains of the phospholipid having a “kinked” profile

Answer 6

Prevents phospholipids from becoming too closely packed together

Allows fluid dynamic membrane

Question 7

Describe the formation of liposomes

Answer 7

Type of spherical vesicle

• Phospholipids placed in water, phospholipids aggregate (automatically arrange themselves) into bimolecular sheets - double bilayer of phospolipids where hydrophobic fatty acid tails are facing inwards away from water and the hydrophillic heads are facing towards the water
• Liposomes formed, separates the two aqueous phases

Question 8

Why do we have charge assymetry?

Answer 8

Different components inside and outside membranes, therefore, charge assymetry

Question 9

State 3 enzymes involved in mantaining membrane assymetry

Answer 9

1. Flipases
2. Flopases
3. Scramblases

Question 10

State the function of flippases

Answer 10

Transfer / move / “flip” phospholipids from inner lumen to outer side / cystolic side of membrane

Specific flippases for specific phospholipids

Question 11

State the function of floppases

Answer 11

Transfer / move / “flip” phosphollipids from outer sode / cystolic side of membrane to inner lumen

Question 12

State the function of scramblases

Answer 12

Ensure equal number of phospholipids on both sides of bilayer by random transfer of phospholipids between each monolayer (inner layer and outer layer)

Question 13

Diagram showing enzymes maintainining membrane assymetry

Answer 13

RECOGNISE FUNCTIONS OF:

1. Flippase
2. Floppase
3. Scramblase

Question 14

Breifly describe the structure of glycolipids

Answer 14

Sugar containing lipid molecule

Sugar group orientated towards outside of cell

Question 15

State the function of gangliosides

Answer 15

Type of glycolipid
Has attached oligosachharides
Important role in surface of nerve cells
Ganglioside Gm1 - acts as surface receptor to bacterial toxin which causes cholera

Question 16

State the function of cholestrol in membranes

Answer 16

Found in eukaryotic plasma membranes only

Oriente / fit between phospholipids in bilayer, hydroxyl heads of cholestrol are close to polar head groups of phosholipids
‘
PARTIALLY IMOBILISING PHOSPHOLIPID MOLECULES This leads to membrane becoming more rigid, less fluid, less permeable, less deformable

(ACTS AS A SPACER) Prevents phase transitioning in membranes - prevents membrane from freezing

Question 17

State 2 factors which affect the fluidity of the phospholipid membrane

Answer 17

1. Fatty acid chain length - shorter fatty acid chain length means the chains are less likey to interact with each other, more fluidity
2. Cis double bonds - higher number of cis bonds = more kinks = phospholipids less closely packed, more cholestrol can fit “snugly” in between - membrane spacer - preventing phase transitions (prevents membranes from freezing), allowing membranes to be fluid at lower temperatures

Question 18

What is glycocalyx?

Answer 18

Carbohyrdate rich zone on surface of cell
Consists of

Glycolipids
Oligosaccharides

Question 19

Selectins

Answer 19

Proteins that bind to the cell surface and mediate cell-cell adhesions

Provide surface markers used to identify certain cells

Question 20

State 4 membrane proteins and their functions

Answer 20

Transporters: transport ions, metabolites, nutrients

Anchors: Anchor membrane to macromolecules

Receptors: Detect external signals

Enzymes: Carry out specific reactions

Question 21

State 2 membrane proteins found in red blood cell membranes and their functions

Answer 21

Spectrin - cytoplasmic side of membrane
Ankyrin - inner side of membrane - links ankyrin to transmembrane proteins

BOTH - give RBC characteristic shape

Question 22

State 4 protein-membrane associations

Answer 22

Transmembrane

Lipid-linked

Protein attached

Monolayer associated