Cell Surface Mebrane

Question 1

Role of membranes

Answer 1

• control the exchange of materials they are partiall permeable
• form compartments within cells
• play role in cell signalling by acting as an interface for communication between cells

Question 2

Why is the fluid mosaic model called the fluid mosaic model

Answer 2

Described as fluid because
- phospholipid and proteins can move around
- Phospholipid move sideways within own layer
Described as mosaic because
- scattered pattern produced by the proteins within the phospholipid bilayers looks like mosaic

Question 3

What does the fluid mosaic model helps to explain and what is it composed off

Answer 3

Cell signalling
Cell to cell interactions
Passive and active movement

Composed of
Phospholipid, cholesterol, glycoproteins and glycolipids and transport proteins

Question 4

Glycolipid and glycoproteins

Answer 4

Exists on surface which enables them to act as receptors molecules by binding substances at cell surface
Act as 3 main receptors
- signalling receptors
- receptor involved in endocytosis
- receptor involved in cell adhesion and stabilisation

Acts as antigens for cell to cell recognition

Question 5

Transport proteins

Answer 5

Create hydrophilic channels to allow ions and polar molecules to travel through the membrane
Two type of transport proteins - channel and carrier proteins
Carrier proteins change shape to transport substance
Each transport protein is specific to particular ion or molecule

Question 6

Roles of Cholesterol on the cell surface membrane

Answer 6

Increases fluidity membrane at low temp so it stops it becoming rigid this occurs by stopping phospholipid tails packing too closely together
Decreases fluidity of membrane at high temp by stabilising membrane this occurs by cholesterol binding to tails of phospholipid which causes phospholipid packing closely together
Cholesterol increases the mechanical strength and stability

Question 7

Describe the phospholipid of membranes

Answer 7

Forms a bilateral which acts as a barriers to most water soluble substances ensuring water soluble molecules cannot leak out of cells and unwanted water soluble cannot get in
They can be chemically modified to act as signallling molecules moving within belayer to activists other molecules
Phospholipid I layer composed of two layers of phospholipid hydrophobic tails face inwards hydrophilic head outwards

Question 8

What factors affect membrane structure and permeability

Answer 8

The permeability of cell membrane is affected by different factors such as temperature and solvent concentration

Question 9

How does temperature affect membrane structure and permeability

Answer 9

Proteins and lipids affect by temperature
As temp increases- lipids become more fluid this reduces the effectiveness of the cell membrane as a barrier to polar molecules
Temperature can effect the proteins leading them to denature distrusting the-membranes structure

Question 10

How does solvent concentration affect membrane structure and permeability

Answer 10

Organic solvents can increase cell membrane e permeability as they dissolve the lipids in the membrane causing membrane to lose its structure