chap 3 biological molecules

• carbohydrates are made up of carbon, hydrogen and oxygen
• the organic molecule with hydrogen and oxygen ratio 2:1

  carbohydrate
• double sugars

  maltose and sucrose
• how to test for reducing sugar?

  shake equal food sample with benedict's solution and place test- tube in a boiling water bath
• when there is no reducing sugar solution remains blue
• when there is traces of reducing sugar, benedict's solution forms a green precipitate
• when there is moderate amounts of reducing sugar, benedict's solution forms a orange or yellow precipitate
• when there is large amounts of reducing sugar, benedict's solution forms a brick-red precipitate
• carbohydrates are used as an immediate source of energy
• fats are used for insulation and long-term source of energy
• proteins are used for growth and repair of cells, synthesis of some hormones and enzymes, and formation of antibodies to combat diseases
• many glucose molecules can synthesise starch, cellulose and glycogen
• starch is a storage form of carbohydrates in plants, digesting into glucose to provide energy for cell activities
• cellulose protects plant cells from bursting or damage
• glycogen is a storage form of carbohydrates in mammals, digesting to glucose to provide energy for cell activities
• starch can be detected by adding few drops of iodine solution, which produces a blue- black colour if starch is present
• fats are made up of carbon, hydrogen and oxygen, but containing less oxygen in proportion to hydrogen
• fats can be broken down into simpler compounds such as fatty acids and glycerol
• how to test for fats?

  shake 2 cm3 of ethanol and drop of liquid sample, then shake 2 cm3 water with the mixture, where a white emulsion would form in the presence of fats
• how to test for fats if the food sample is solid

  • crush solid sample into small pieces
  • add the ethanol and shake
  • decant the mixture into another test tube containing water and shake
• proteins are made up of carbon, hydrogen, oxygen and nitrogen
• many amino acids molecules are joined in a linear manner to form a polypeptide, which when folded together into a more complex 3- dimensional shape, forms a protein
• how to test for protein

  shake equal amounts of food sample with biuret solution and let stand for 5 minutes. when it turns a violet colour, protein is present
• amylase

  starch -> maltose
• maltase

  maltose -> glucose
• protease

  protein -> polypeptides -> amino acids
• lipase

  fats -> fatty acids + glycerol
• enzymes can catalyse the process to build up complex substances or break down complex substance
• building up substances (anabolic reaction): amino acids -> protein
• breaking down substances (catabolic): glucose broken down to release energy
• explain mode of action of enzymes

  • substrate binds to the 3D shape complementarily shaped active site of the enzyme, an enzyme- substrate complex is formed
  • while the substrate is attached to the active site, a chemical reaction occurs
  • the substrate molecules is then converted into product molecules
  • the product molecules separate from the enzyme
  • the enzyme, molecule remains unchanged and is free to combine again with more substrate molecules
• explain mode of action of enzymes using lock and key

  • substrate binds to the 3D shape complementarily shaped active site of the enzyme, an enzyme- substrate complex is formed
  • the enzyme is like a lock and substrate is like the key
  • the substrate fits into the enzyme just like a key fits into a lock
• characteristics of enzymes

  • speed up chemical reactions
  • specific in action
  • required in small amounts and remain chemically unchanged
  • are affected by temperature
  • are affected by pH level
• they speed up chemical reactions by lowering the activation energy needed to start the reaction
• enzymes are specific in action as they have a active site that is complementary to a substrate
• enzymes are less active at lower temperatures as kinetic energy of molecules are low, causing movement of particles to be slower and hence, the rate of collision between substrate molecules and enzymes is very low
• optimum temperature of human enzymes is about 40 - 45 degrees
• at temperatures above optimum temperatures, active site of enzyme molecules begins to lose its original shape and is no longer complementary to the shape of substrate molecules, hence, denaturing
• enzyme activity against pH level graphs for enzymes are always symmetrical
• optimum pH of protease in stomach is 1