lipids

• •Many alpha glucose molecules can join via glycosidic bonds to form the polysaccharide, starch. This is a chemical energy store. There are two forms of this polysaccharide, amylose and amylopectin.

  • cellulose is a straight chain polysaccharide, formed by the joining of many beta glucose molecules. The only way in which these molecules can join is if alternate molecules are turned upside down.

  •A very branched polysaccharide is glycogen. This is important in animals and fungi as an energy store.
• What molecules are lipids made up of?

  Glycerol and fatty acids
• What are lipids used for?

  Insulation and energy source
• What foods contain lipids?

  oils
• One lipid macromolecule is a triglyceride. A triglyceride is made up of one glycerol molecule and three fatty acids. Fatty acids are carboxylic acids- they contain a carboxyl group (-COOH) attached to a hydrocarbon chain.

  
• glycerol is an alcohol

  
• Fatty acids can be saturated or unsaturated.

  
• saturated - No double bonds between carbon atoms
• Mono unsaturated - One double bond between carbon atoms
• poly unsaturated - More than one double bond between carbon atoms
• saturated fats have straight molecules as there are only single bonds. these can pack together tightly. the closeness means they bond together tightly, and more energy is needed to separate them.

  saturated fats have higher melting points and tend to be solids

  
• unsaturated fats have less straight molecules as the double bond gives them a 'kink'. these pack together less tightly. less closeness means they don't bond together so tightly, and less energy is needed to separate them.

  unsaturated fats have lower melting points and are liquids.

  
• A triglyceride is made up of one glycerol molecule and three fatty acids. Triglycerides are formed by a condensation reaction called Esterification. Ester bonds are formed between glycerol and fatty acids and three molecules of water are produced.

  
• Triglycerides are broken down by hydrolysis reactions in which ester bonds are broken.
• Phospholipids are modified triglycerides. One of the fatty acid chains in the triglyceride molecules is replaced by a phosphate group.

  
• Phospholipids have:

  •A non-polar tail made up of the fatty acid chains

  •A polar head made up of the phosphate group