Lipids

• Predominantly carbon and hydrogen
• some oxygen
• insoluble in water
• soluble in organic solvents e.g. acetone



• comprise glycerol + fatty acids
• joined by condensation reaction between hydroxyl groups on glycerol and on fatty acid = anabolic or synthesis reaction
• results in ester bond
• and release of water
• parted by hydrolysis reaction with use of water = catabolic or degradation reaction



• hydrocarbon chains are non-polar
• carboxyl end group is polar
• chains can be saturated or unsaturated
• unsaturated fatty acids lower melting point so oils (liquid at room temp) have more unsaturated FA than fats (solid at room temp)

Roles of Lipids

• lipids are energy stores
• glycerol and fatty acids feed into the catabolic pathways releasing energy
• catabolism of fatty acids = -oxidation
• lipids are stored as triglyceride droplets suspended in cytoplasm
• release more energy per gram than carbohydrates (2x) but require oxygen
• (aerobic respiration of carbohydrate is more efficient than anaerobic respiration but anaerobic respiration can occur)
• oxidation of lipids releases metabolic water
• plant stores are oils - found in seeds
• animal stores are fats found as adipose tissue just below skin
• adipose tissue also functions to protect organs, provide insulation, give buoyancy in water

Waxes

• similar to lipids but not glycerol - longer chain alcohols instead
• found on external surfaces of plants and animals
• very water repellent so provide waterproofing

Phospholipids

• similar structure to lipids but
• only 2 FA
• third hydroxyl has a phosphate group attached
• phosphate group is polar
• so phospholipids orientate with hydrophilic phosphate head group towards water
• hydrophobic FA tails away from water
• results in micelle
• show abbreviated diagram of phospholipid
• function is as component of membranes

Questions on Lipids

• Lipids are formed from glycerol and what other group of biomolecules
• Draw the structure of glycerol
• What type of reaction is involved in the anabolism of lipids
• Is water used up or produced in this reaction
• What type of bond is produced
• Fatty acids comprise 2 main regions. What are these regions and are they polar or non-polar
• What feature of fatty acids determine whether the resulting lipid is an oil or a fat
• State 4 functions of lipids
• How does the structure of phospholipids differ from that of lipids
• With respect to water, what are the properties of lipids