section 1

• Most carbohydrates, proteins and nucleic acids are polymers.
• Polymers - large, complex molecules composed of long chains of monomers joined together.
• Monomers - small basic molecular units that can form a polymer.
• Examples of monomers include monosaccharides, amino acids and nucleotides.
• Most biological polymers are formed from their monomers by condensation reactions.
• A condensation reaction forms a chemical bond between monomers, releasing a molecule of water.
• Biological polymers can be broken down into monomers by hydrolysis reactions.
• A hydrolysis reaction breaks the chemical bond between monomers using a water molecule.
• All carbohydrates contain the elements C, H and O.
• The monomers that carbohydrates are made from are monosaccharides.
• Examples of monosaccharides are glucose, fructose and galactose.
• Glucose is a hexose sugar - a monosaccharide with six carbon atoms in each molecule.
• Two types of glucose - alpha and beta glucose - they are isomers.
• Alpha glucose

  
• Beta glucose

  
• A disaccharide is formed when two monosaccharides join together.
• Monosaccharides are joined together by condensation reactions - a glycosidic bond forms between the two monosaccharides as a molecule of water is released.
• Sucrose is a disaccharide formed from a condensation reaction between a glucose molecule and a fructose molecule.
• Lactose is a disaccharide formed from a glucose molecule and a galactose molecule.
• To test for sugars you use the benedicts test. The test differs depending on whether you‘re testing for reducing or non-reducing sugars.
• Reducing sugars include all monosaccharides and some disaccharides.
• Test for reducing sugars - add benedicts reagent to a sample and heat in a water bath that has been brought to a boil. If the test is positive it will form a coloured precipitate. Turns from blue solution to brick red precipitate. The higher the concentration of reducing sugar, the further the colour change goes.
• Test for non-reducing sugars - first break them down into monosaccharides by getting a new sample of solution and adding dilute hydrochloric acid and carefully heat in a water bath that has been brought to the boil. Then neutralise it by adding sodium hydrogencarbonate. Finally just carry out the Benedict‘s test as you would for a reducing sugar.
• A polysaccharide is formed when more than two monosaccharides are joined together by condensation reactions.
• Polysaccharides can be broken down into monosaccharides by hydrolysis reactions.
• Starch:

  • cells get energy from glucose. Plants store excess glucose as starch. Starch is a mixture of two polysaccharides of alpha glucose.
• Two types of starch:

  • amylose
  • amylopectin
• Amylose - long, unbranched chain of alpha glucose. The angles of glycosidic bonds give it a coiled structure. This makes it compact so it’s good for storage because you can fit more in to a small space.
• Amylopectin - long, branched chain of alpha glucose. Its side branches allow the enzymes to break down the molecule to get at the glycosidic bonds easily. This means that the glucose can be released quickly.
• Starch is insoluble in water and doesn’t affect water potential so it doesn’t cause water to enter cells by osmosis, which would make them swell. This makes it good for storage.
• Glycogen - animal cells get energy from glucose too. But animals store excess glucose as glycogen. Its structure is similar to amylopectin, except it has loads more side branches coming off it. Loads of branches means that stored glucose can be released quickly, which is important for energy release in animals. It’s also a very good compact molecule, so it’s good for storage.
• Cellulose - made of long, unbranched chains of beta glucose. When beta glucose molecules bond, they form straigh cellulose chains. The cellulose chains are linked together by hydrogen bonds to form strong fibres called microfibrils. The strong fibres mean cellulose provides structural support for cells.
• Iodine test for starch - add iodine dissolved in potassium iodide solution to the test sample. If there is starch present, the sample changes from browny-orange to a dark, blue-black colour.
• Lipids - made from a variety of different components, but they all contain hydrocarbons. The components they’re made from relates to the lipid’s function.
• There are two types of lipid:

  • triglycerides
  • phospholipids
• Triglycerides - have one molecule of glycerol with three fatty acids attached to it. Fatty acid molecules have long tails made up of hydrocarbons. The tails are hydrophobic. These tails make lipids insoluble in water.
• Fatty acids - all fatty acids consist of the same basic structure, but the hydrocarbon tail varies.
• There are two types of fatty acids - saturated and unsaturated. The difference is their hydrocarbon tails.
• Saturated fatty acids - don’t have any double bonds between their carbon atoms. The fatty acid is saturated with hydrogen.
• Unsaturated fatty acids - do have double bonds between carbon atoms, which cause the chain to kink.