sugars

• Most carbohydrates, proteins and nucleic acids are polymers. Polymers are large, complex molecules composed of long chains of monomers joined. 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. Breaking down polymers

  Biological polymers can be broken down into monomers by hydrolysis reactions. A hydrolysis reaction breaks the chemical bond between monomers using a water molecule. It’s basically the opposite of a condensation reaction.

  
  

  
  

  
  

  
  
• All carbohydrates contain the elements C, H and O. The monomers that carbohydrates are made from are monosaccharides, e.g. glucose, fructose and galactose.

  Glucose is a hexose sugar — a monosaccharide with six carbon atoms in each molecule. There are two types of glucose, alpha (a) and beta (b) glucose — they’re isomers (molecules with the same molecular formula as each other, but with the atoms connected in a different way).

  
• A disaccharide is formed when two monosaccharides join together. Monosaccharides are joined together by condensation reactions (see page 21) — 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 another disaccharide, formed from a glucose molecule and a galactose molecule.
• The higher the concentration of reducing sugar, the further the colour change 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, or to remove the precipitate and use a colorimeter
• What is a non-reducing sugar example mentioned in the study material?

  Sucrose
• What does a negative result in the reducing sugars test indicate?


  There could still be a non-reducing sugar present
• What is the first step to test for non-reducing sugars?


  Get a new sample of the test solution
• What should be added to the new sample to break down non-reducing sugars?

  Dilute hydrochloric acid
• How should the sample be heated to break down non-reducing sugars?


  In a water bath that’s been brought to the boil
• What is the purpose of adding sodium hydrogencarbonate after heating?


  To neutralise the solution
• What test is performed after neutralising the solution?

  The Benedict’s test
• What are the steps to test for non-reducing sugars?


  1. Get a new sample of the test solution.
  2. Add dilute hydrochloric acid.
  3. Heat in a boiling water bath.
  4. Neutralise with sodium hydrogencarbonate.
  5. Perform the Benedict’s test.
• Reducing sugars include all monosaccharides and some disaccharides, e.g. maltose and lactose.
• you add Benedict’s reagent (which is blue) to a sample and heat it in a water bath that’s been brought to the boil. If the test’s positive it will form a coloured precipitate — solid particles suspended in the solution. The colour of the precipitate changes as shown in Figure 2.

  
• The higher the concentration of reducing sugar, the further the colour change 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, or to remove the precipitate and use a colorimeter to measure the absorbance of the remaining Benedict’s reagent.
• Hexose


  A type of sugar that contains six carbon atoms
• Monosaccharides


  Monomers that carbohydrates are made from
• Isomers


  Molecules with the same molecular formula but atoms connected in a different way
• Glucose


  A monosaccharide with six carbon atoms, two types: alpha (a) and beta (b)
• Condensation reaction


  A reaction where a molecule of water is released, often accompanied by the formation of a new bond (in this case, a glycosidic bond).
• Glycosidic bond


  A type of bond that forms between two sugar molecules (monosaccharides) through a condensation reaction, releasing water.
• Glycosidic


  Referring to the type of bond that forms between sugar molecules (monosaccharides) through a condensation reaction.
• Monosaccharide


  A single sugar molecule that cannot be broken down further into simpler compounds.
• Disaccharide


  A molecule formed when two monosaccharides (single sugar molecules) bond together through a condensation reaction.