Lipids

Lipids  Lipids are fats (solid), oils (liquid), waxes and phospholipids  Lipids contain carbon (C), Oxygen (O), Hydrogen (H) and sometimes other atoms, e.g. phosphorus (P)  Lipids are insoluble in water  Triglyceride lipids are composed of two types of molecule: glycerol and fatty acids

HH HH HH H H C C C Lipid Formation - Triglycerides HOCO (CH 2 ) n CH 3 HOCO HOCO GlycerolFatty Acids Condensation Reactions O O O O O O

Lipids - Triglycerides + 3H 2 O H H H H H C C C CO CO CO (CH 2 ) n CH 3 O O O Now highlight the ester bond

Lipids - Triglycerides + 3H 2 O H H H H H C C C CO CO CO (CH 2 ) n CH 3 O O O O O O

Lipids - Triglycerides  Three fatty acids are joined to a glycerol molecule by ester bonds  The carboxyl ends of the fatty acids join to the hydroxyl ends of glycerol  This is a condensation reaction - for each fatty acid that joins to glycerol, a molecule of water is lost.

Lipids - Triglycerides Fatty Acid Fatty Acid Fatty Acid G l y c e r o l

 The Glycerol part of a triglyceride always has the same structure  The fatty acids are composed of hydrocarbon chains which can differ in length  It is the structure of the fatty acids that give different lipids their different properties

Saturated and Unsaturated Fats  Saturated fats have a full complement of single bonded Hydrogen atoms in their fatty acid hydrocarbon chains  Unsaturated fats contain double bonds, and therefore could accept more Hydrogen atoms

Saturated Fatty Acids Are solid at room temperature The hydrocarbon chain is fully saturated with hydrogen. Found in animal fats Examples: Stearic Acid, Butyric Acid

Unsaturated Fats  Have one or more double bonds.  Liquid at room temperature  Found in vegetable oils, fish oils

Functions of Fats & Oils  Energy & Energy Storage  Waterproofing  Plasma Membranes (Phospholipids)  Insulation (e.g.blubber)  Protection (e.g. of body organs)  Buoyancy (e.g seals), Water storage (eg desert animals)

Phospholipids Hydrophilic ‘head’ Hydrophobic ‘tails’

Phospholipids  A phospholipid molecule consists of a hydrophilic polar head group and a hydrophobic tail  They are the main constituents of cell membranes  The hydrophobic tail is made up of two fatty acid chains – water hating  The third chain is replaced by a phosphate group water-loving.  When phospholipid molecules are placed in water, their hydrophilic heads tend to face water and the hydrophobic tails are forced to stick together, forming a bilayer

Functions of Steroids & Waxes extra to syllabus  Steroids –Vitamin D –Cholesterol (bile acids & hormones) –Progesterone & Testosterone  Waxes –Leaf Surfaces (prevents water loss) –Bee nests (structure) –Bird Feathers and mammal fur (water loss & protection)

Relating Structure to Function –Fats are energy storage molecules. Their insolubility makes them ideal for storage as they do not diffuse out of cells –They are insoluble because a large part of the molecule is hydrophobic –Fats possess more energy per molecule than any other nutrient so they can store a lot of energy in a small space.

Relating Structure to Function  Fats conduct heat very slowly, so they are good insulators. They are usually stored under the skin so help to retain body heat  Fats help to maintain healthy hair and skin. They form a water- repellent layer over the surface.