Lipids

• High energy yield=important energy source, which can be respired
• Energy store: plants=lipid droplets, animals=adipose tissues
• Acts as an insulating layer: thermal insulation under the skin of mammals and eletrical insulator around nerve cells
• Biological membranes are made from lipids

• Includes fats and oils which are formed from a condensation reaction between 3 fatty acids and a glycerol molecule

• Saturated: None of the C atoms are linked with a double bond in the hydrocarbon chain
• Unsaturated: At least one doulbe bond between C atoms in the hydrocarbon chain

• 2 fatty acids chains bonded to the glycerol, instead of 3 in a triglyceride
• The third OH group is occupied by a phosphate group
• 2 fatty acids chains are hydrophobic, whereas the phosphate molecule is hydrophlic
• The two regions within the phospholipid give biological membranes their unique properties

                                Triglyceride                            Phospholipid

Structure                 G+3FA                                     G+2FA+P

Function                  Energy source                       Plama membrane:

                               and energy store                    only allows certain ions+molecules to pass                                                                                          through

• Similar molecule to a phospholipid:hydrophilic+hydrophobic regions
• Important part of plasma membranes in cells=maintains a suitable level of fluidity in the membrane
• Cholesterol can bind to phospholipids=prevents membrane becoming too fluid
• Cholesterol prevents fatty acids coming together and crystalising=keeps the membrane fluid