Cell membrane

Question 1

Cell surface membranes

Answer 1

A barrier between a cell and its environment which controls what enters and what leaves

Question 2

Organelles membranes

Answer 2

A barrier which divides cell into different compartments and separates the organelles from cytoplasm

Question 3

What model describes the structure of a cell membrane?

Answer 3

The fluid mosaic model

Question 4

Why is the membrane described as ‘fluid’?

Answer 4

Because it is mainly composed of continuous double layer of phospholipid molecules (phospholipid bilayer)
These molecules constantly move as well as proteins which can move throughout membrane

Question 5

Why is the membrane described as a mosaic?

Answer 5

Because scattered throughout the phospholipid bilayer are carrier proteins, channel proteins, receptor proteins, cholesterol, glycolipids ane glycoproteins

Question 6

List of molecules that make up the membrane

Answer 6

Phospholipids
Intrinsic proteins (channel and carrier)
Extrinsic proteins (receptors)
Cholesterol
Glycolipid
Glycoprotein

Question 7

Phospholipid bilayerstructure

Answer 7

A hydrophilic head facing outwards of the cell and into the cytoplasm to attract water
And hydrophobic tails centred in inside to repel water

Question 8

What does the phospholipid bilayer allow to dissolve through?

Answer 8

Small non polar molecules due to non polar fatty acids in the centre eg o2 and co2
Water because it’s so small despite being polar

Question 9

Channel proteins

Answer 9

For facilitated diffusion of large molecules such as glucose with a large pore to transport in/out of cell

Question 10

Carrier proteins

Answer 10

For facilitated diffusion of largemolecules by changing the tertiary structure to release large molecules to other side once ion bonded to it

Question 11

Extrinsic proteins

Answer 11

Act as receptors on surface of membrane to detect chemicals released from other cells to signal to cell to respond

Question 12

What is cholesterol?

Answer 12

A type of lipid present in all cell membranes except bacteria cell membranes to provide stability

Question 13

Role of cholesterol

Answer 13

Binds to hydrophobic fatty acids in phospholipids to pack them closer together and restrict movement = more rigid and maintains shape
Create further barrier to polar substances due to hydrophobic properties

Question 14

Glycoproteins

Answer 14

A carbohydrate (glyco) bonded to a membrane protein

Question 15

Glycolipid

Answer 15

A carbohydrate (glyco) bonded to a phospholipid (lipid)

Question 16

What affects cell membrane’s permeability?

Answer 16

Temperature which affects movement of phospholipids thus affecting membrane structure and permeability

Question 17

Effect of temperature on membrane permeability description of a graph

Answer 17

Below 0°c = very high permeability
0°c = rapidly decreased permeability
0°c to 45°c = begins increasing
Above 45°c = very high permeability

Question 18

Why is below 0°c the permeability is very high?

Answer 18

Because at very cold temperatures the protein membranes have denatured causing increased permeability

Question 19

Why is the permeability very low at 0°c?

Answer 19

Because the phospholipids have little energy so less fluid due to moving less so won’t allow molecules to enter

Question 20

Why does the permeability begin to increase from 0°c to 45°c?

Answer 20

As temp increases, phospholipids move more due to having more energy so allow more molecules to enter

Question 21

Why does the permeability increase rapidly above 45°c?

Answer 21

The membrane begins to break down due to increased energy of phospholipids
Proteins begin denaturing again so cannot control what leaves or enters (permeable)