Lecture 11

Question 1

the plasma membrane

Answer 1

is the boundary that separated the living cell from its surroundings

exhibits selectively permeability allowing some substances to cross it more easily than others
- this regulates the cells molecular traffic

Question 2

Fluid mosaic structure of plasma membrane

Answer 2

phospholipids are most abundant lipids- hydrophobic tails and hydrophilic heads that create the phospholipids bilayer

it has other molecules within it like proteins cholesterol and glycoproteins

Question 3

Fluidity of membranes

Answer 3

phospholipids in the plasma membrane can move within the bilayer

most of the lipids and some proteins drift laterally
rarely does a molecule flip transversely across the membrane

Question 4

Cholesterol within a cell membrane

Answer 4

can act as a fluidity buffer to prevent drastic changes in membrane fluidity caused by external temperature changes

the steroid cholesterol has different effects on membrane fluidity at different temperatures

at warm temperatures cholesterol restricts movement of phospholipids but at cool temperatures it maintains fluidity

Question 5

factors affecting membrane fluidity

Answer 5

unsaturated versus saturated hydrocarbon tails (unsaturated more fluid because they prevent packing)

cholesterol within the animal cell membranes affects fluidity

temperature

Question 6

Effect of temperature on membrane fluidity

Answer 6

as temperatures cool, membranes switch from a fluid state to a solid state

the temperature at which a membrane solidifies depends on the types of lipids

Question 7

Experiments to confirm fluid mosaic model

Answer 7

freeze-fracture studies of the plasma membrane supported the fluid mosaic model

freeze-fracture is a specialised preparation technique that splits a membrane along the middle of the phospholipid bilayer

Question 8

Frye and Edidin

Answer 8

Rhodamine and fluorescent-labelled antibodies against human and mice protein (Evidence the plasma membrane is fluid)

Question 9

Membrane associated proteins

Answer 9

transmembrane
monolayer associated
lipid-linked
protein attached

Question 10

functions of membrane proteins

Answer 10

transport
enzymatic activity
signal transduction
cell-cell recognition
intercellular joining
attachment to the cytoskeleton and extracellular matrix

Question 11

facilitated diffusion

Answer 11

passive transport aided by proteins

carrier proteins undergo a subtle change in shape that translocated the solute binding site across the membrane

this change in shape can be triggered by the binding and release of the transported molecule

Question 12

Two types of transport proteins

Answer 12

channel proteins
carrier proteins

Question 13

Diffusion of two solutes

Answer 13

when there are 2 solutes, one either side of a membrane, they will move down their own concentration gradients, until equilibrium is reached for each solute one is not dependant on the other

Question 14

Osmosis

Answer 14

the diffusion of water across a selectively permeable membrane

water diffuses across a membrane from the region of lower solute concentration the region of higher solute concentration

Question 15

Isotonic solution

Answer 15

solute concentration is the same as that inside the cell
- no net movement across the plasma membrane

Question 16

Hypotonic solution

Answer 16

solute concentration is less than inside the cell

• cell gains water to try to equal the concentration of the solution –> cell bursts/ lyses

Question 17

Hypertonic solution

Answer 17

solute concentration of a solution is greater than that inside the cell: cell does water to try to equal the concentration of the solution –> cell shrivels

Question 18

reactions to solute concentration

Answer 18

animals- lysed or shrivelled

plant cells will become either turgid flaccid or plasmolysed

Question 19

Blebbing

Answer 19

dissociation of plasma membrane from actin cytoskeleton

Question 20

Aquaporins

Answer 20

allows osmosis to occur extremely rapidly, nothing larger than water can fit
the passage of ions is prevented- they’re repelled by positively charged amino acids at the narrowest part

Question 21

Active transport

Answer 21

uses energy to move solutes against their concentration gradient

Question 22

Three types of transporters

Answer 22

uniporter- one solute one direction

symporter- two solutes in same direction

antiporter- two solutes in opposite directions