S

1.3 lipids

Name the two groups of lipids

  • triglycerides

  • Phospholipids

Describe the structure of a fatty acid (RCOOH)

  • variable R-group - hydrocarbon chain (this may be saturated or unsaturated

  • -COOH = carb oxygen group

Difference between a saturated and unsaturated fatty acid

Saturated — no C=C (double carbon bonds) in hydrocarbon chain so all carbons are fully saturated with hydrogen

Unsaturated — one or more C=C (double carbon bonds) in hydrocarbon chain, causing a bend/ kink

Describe how triglycerides form

  • 1 glycerol molecule and 3 fatty acids

  • 3 condensation reactions

  • Removing 3 water molecules

  • Forming 3 ester bonds

Function of triglycerides

  • energy storage

How their properties relate to their structure

  • high ratio of C-H bonds to carbon atoms in hydrocarbon chain. So they are used in respiration to release more energy than same mass carbohydrates

  • Hydrophobic/ non polar fatty acids, so insoluble in water (clump together as droplets). So there’s no effect on water potential of cell, or can be used for waterproofing

Describe how phospholipids form

  • 1 glycerol molecules, 2 fatty acids and a phosphate containing group

  • 3 condensation reactions

  • Removing 3 water molecules

  • Forming 3 ester bonds

Function of phospholipids

  • form a bilayer in cell membrane, allowing diffusion of lipid soluble (non polar) or very small substances and restricting the movement of water soluble (polar) or larger substances

How their properties relate to their structure

  • phosphate heads are hydrophillic. Attracted to water so point towards aqueous environment either side of the membrane

  • Fatty acid tails are hydrophobic. Repelled by water so point away from water to the interior of the membrane

What is the test for lipids

  1. Add ethanol

  2. Shake to dissolve lipids

  3. Add water

  4. Positive result = milky white emulsion