is a variable group contains C, H ,O atoms high ratio of H:O than carbohydrates insoluble in water eg triglycerides, phospholipids, cholesterol etc Triglycerides they are insoluble in water, but soluble in ethanol they are less dense than water (they float) act as good insulators – both electrical and thermal. contains the molecule glycerol and three fatty acids. Three fatty acids and one glycerol molecule join together in a condensation reaction forming ester linkage Three molecules of water are released The reaction can be reversed using hydrolysis to turn the triglyceride back into its individual molecules Fatty acids Have long chains of C and H atoms. Saturated fatty acids has only single C-O bonds. An unsaturated fatty acid will have carbon-to-carbon (C=C) double bonds It makes the molecules in the lipid push apart and so makes them more fluid Unsaturated lipids tend to have lower melting points than saturated lipids. Explain how the molecular structure of triglycerides is related to their functions. possess hydrophobic tails of fatty acids; which cause the molecule to be insoluble in water; they are not so easily dissolved out of the cell; this functions to provide the properties of the phospholipid bilayer in cell membranes; acts as energy store for the cell; due to their higher proportion of hydrogen compared to carbohydrates; as a result the breakdown of triglycerides yields ore energy; due to the lower proportion of oxygen to carbon that requires more oxygen for complete oxidation to occur. triglycerides also float in water due to their lighter density; this enables them to aid in the buoyancy of aquatic animals; Phospholipids one glycerol molecule and two fatty acid molecules bonded to it from condensation reactions, producing these ester bonds. a phosphate group is bonded covalently to the third hydroxyl group on the glycerol A phospholipid therefore consists of two parts: the phosphate head and the fatty acid tails. The head is very hydrophilic (i.e. water-loving) and the tails are hydrophobic (i.e. water-hating) In H2O, phospholipid molecules arrange into a bilayer: hydrophilic heads facing outwards into the water and hydrophobic tails facing inwards, avoiding water. This is the basic structure of a cell membrane. Lipids functions energy storage making biological membranes insulation protection eg protecting plants from drying up boyancy acting as hormones