Carbohydrates

• Most carbohydrates are polymers
• Polymers are large, complex molecules that are composed of long chains of monomers joined together
• Monomers are small, basic molecular units
• Examples of monomers include monosaccharides, amino acids and nucleotides
• All carbohydrates contain the elements C, H and O
• The monomers carbohydrates are made from are monosaccharides
• Three examples of monosaccharides are glucose, fructose and galactose
• Glucose is a hexose sugar
• A hexose sugar is a monosaccharide with 6 carbon atoms in each molecules
• There are two types of glucose alpha and beta
• Both types of glucose are isomers
• A condensation reaction when 2 molecules join together with the formation of a new chemical bond and a water molecule is released when the bond is formed
• Monosaccharides are joined together by condensation reactions
• A glycosidic bond forms between 2 monosaccharides as a molecule of water is released.
• A disaccharide is formed when two monosaccharides join together
• An example of a disaccharide is when two alpha glucose molecules are join together by a glycosidic bond to form maltose
• 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
• Polysaccharides are made up of many monomers (monosaccharides) linked together by glycosidic bonds
• Starch, cellulose and glycogen are examples of polysaccharides
• Polymers can be broken down into monomers by hydrolysis
• A hydrolysis reaction breaks the chemical bond between monomers using a water molecule
• Carbohydrates can be broken down into their constituent monosaccharides by hydrolysis reactions
• Sugar is the general term for monosaccharides and disaccharides
• All sugars can be classified as reducing or non-reducing sugars
• The Benedict's test is for sugars however it differs depending on the type of sugar you are testing for
• Reducing sugars include all monosaccharides and some disaccharides
• some examples of disaccharides include maltose and lactose
• Testing for reducing sugars:

  1. You add benedict's reagent to a sample and heat it in a water bath that's been brought to the boil
  2. If the test is positive it will form a coloured precipitate

  Blue --> Green --> Yellow --> Orange --> Brick Red

  
  

  The higher the concentration of reducing sugar, the further the colour changes goes - you can use this to compare the amount of reducing sugar in different solutions. A more accurate way of doing this is to filter the solution and weigh the precipitate
• If your testing for reducing sugars and there is none the solution will remain blue
• If the result of the reducing sugars test is negative, there could still be a non-reducing sugar present.
• To test for non-reducing sugars, like sucrose, first you have to break them down into monosaccharides.
• You do this by getting a new sample of the test solution, adding dilute hydrochloric acid and carefully heating it in a water bath that's been brought to the boil.
• You then neutralise the solution with sodium hydrogencarbonate.
• Then just carry out the Benedicts test as you would for reducing sugar.
• If the test is positive, it will form a coloured precipitate.
• If the non-reducing sugar test is negative, the solution will stay blue, which means it doesn't contain any sugar.
• A polysaccharide is formed when more than two monosaccharides are joined together by condensation reactions
• An example of a polysaccharide is when lots of alpha-glucose molecules join together by glycosidic bonds to form amylose
• Cells get energy from glucose.