Phospholipids

Describe phospholipids

• A type of lipid molecule that are a major component of cell membranes

• They are amphipathic, meaning they contain both:

→ A hydrophilic head

→ Hydrophobic tails

Detailed molecular diagram of a phospholipid

Simple diagram

What does a phospholipid consist of

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  • 1 glycerol molecule, 2 fatty acid chains and 1 phosphate group.

  • Fatty acids are joined to glycerol by ester bonds.

  • The phosphate group is joined to glycerol by a phosphoester

Explain how the structure of phospholipids relate to their function

• Hydrophobic fatty tails create a hydrophobic core when a phospholipid bilayer forms

• The hydrophilic phosphate heads forms h-bonds with water, allowing the cell membrane to be used to compartmentalise

• The composition of phospholipids contributes to the fluidity of cell membrane. Saturated fatty acids - less fluidity. Unsaturated fatty acids - more fluidity

• Phospholipids control membrane protein orientation

How do phospholipids form a bilayer?

• Phospholipids are amphipathic (have hydrophilic and hydrophobic regions).

• Hydrophilic phosphate heads face outwards towards the water on both sides of the membrane.

• Hydrophobic fatty acid tails face inwards, away from water.

• This causes phospholipids to arrange themselves into a bilayer with a hydrophobic core.

Describe how you would test a liquid sample for the prescence of lipid & how you would recognise a positive result

• The emulsion test → Qualitative value

• Lipids will dissolve immediately in organic solvents e.g ethanol

• Add ethanol, shake to mix & then add mixture to a test tube of water

• If lipids are present, a milky emulsion will form

• If no lipid is present, solution remains colourless