Fluid mosaic model

Label the diagram of a plasma membrane

Fluid

The phospholipid bilayer is viscous and individual phospholipids can move position

Mosaic

the phospholipid bilayer is embedded with protiens, resulting in a mosaic of components

Phospholipid bilayer

• The centre of the bilayer is hydrophobic so the membrane doesn’t allow water soluble substances (like ions and polar molecules) to diffuse through it

• Small, non-polar and lipid soluble substances such as CO₂ can diffuse through the membrane

Name the 2 types of membrane proteins:

• Extrinsic - they are found on one surface of the membrane only

• Intrinsic - they span the entire membrane

Protein Channels (pores)

• Some proteins span the whole membrane and act as hydrophilic (allowing water soluble substances through) pores

• They’re very selective and allow ions (Ca, K, etc) that travel in water into and out of the cell

Carrier Proteins

• Allow substances to pass through them in facilitated diffusion e.g glucose

• Act as carriers for active transport, moving substances in and out of the cell against a concentration gradient

Cholesterol

• They add strength to the membranes

• Very hydrophobic so prevent loss of water and ions from cells

• They pull together the fatty acid tails of the phospholipids, making the membrane more rigid and ensure the membrane is less fluid at high temperatures

Glycolipids

• Carbohydrate covalently bonded to the lipid

• Extends from the bilayer into the extrinsic environment outside the cell

• One type of glycolipid found in human Red Blood Cells is involved in the ABO blood type antigens

• They act as recognition sites (ABO blood grouping)

• Help cells attach to one another and so form tissues

• Help maintain the stability of the membrane

Glycoproteins

• Carbohydrate chains are attached to many extrinsic proteins

• These act as cell - surface receptors more specifically for hormones

• They also help cells attach to one another and allow cells to recognise one another