Topic 2.2 - Cell Membrane

Question 1

What is the cell surface membrane?
What is its function?

Answer 1

• Barrier between cell and environment
• Controls what substances enter and exit the cell

Question 2

What are organelle membranes?

Answer 2

• Separates cell components from cytoplasm
• Contains proteins required for function of organelles (e.g. enzymes)

Question 3

What are the four functions of organelle membranes?

Answer 3

• Involved in cell signalling
• Cell recognition
• Acts as a marker / antigen
• Attachment receptor

Question 4

What is the phospholipid bilayer made of?

Answer 4

• Phospholipids
  = Head (polar) > phosphate group + glycerol
  = Uneven distribution of charge
  = Tail (non-polar) = 2x fatty acids
  = Even distribution of charge
• Cholesterol
  = Type of lipid
  = Provides membrane stability
  = Binds to hydrophobic tails
  = Causes restriction of phospholipid movement (less fluid) as they are closely packed together
  = Maintains shape of animal cells

Question 5

Define hydrophobic

Answer 5

Repels water

Question 6

Define hydrophilic

Answer 6

Attracts water

Question 7

What substances can and can’t diffuse through phospholipid bilayer?
Why?

Answer 7

• Can’t
  = Water soluble substances
  = Polar molecules
• Can
  = Small, non-polar substances
  = Water

They can’t diffuse through phospholipid bilayer as centre is hydrophobic

Question 8

What are the two components of cell surface membrane?

Answer 8

• Glycoproteins = Proteins with carbohydrate chain attached
• Glycolipids = Lipids with carbohydrate chain attached

Question 9

Describe the fluid mosaic model

Answer 9

• Describes the arrangement of molecules in the plasma membrane
• Fluid = Phospholipids are not attached to each other
  = form a continuous bilayer that is constantly moving freely
• Mosaic = Phospholipids and proteins are scattered through bilayer
  = Proteins increase permeability of plasma membrane

Question 10

What are the two types of transport proteins?
What molecules do they help diffuse through?

Answer 10

• Carrier proteins = Transport large molecules (e.g. glucose or amino acids)
• Channel proteins = Pores in the membrane
  = Allows charged (polar) molecules / ions to diffuse through by facilitated diffusion

Question 11

What transport protein does water diffuse through?
What transport protein do large molecules diffuse through?
What transport protein do polar molecules diffuse through?

Answer 11

Water > aquaporins
Large molecules > carrier proteins
Polar molecules > channel proteins