digestive system

• what are the roles of the organs in the digestive system?


  liver = produces bile, stores glycogen, removes toxins, stores vitamins and iron, breaks down excess proteins

  stomach = protein digestion using protease. has hydrochloric acid which kills bacteria. provides optimum pH for protease to work

  small intestine = breaking down large insoluble molecules into smaller soluble molecules and absorption. makes lipases, carbohydrases and proteases

  large intestine = water is absorbed from undigested food
• what are carbohydrate molecules made up of?


  1. simple sugars are carbohydrates that contain only one or two sugar units - glucose
  2. complex carbohydrates such as starch are made up of long chains of simple sugars bonded together.
• what are lipids made up of?


  lipids are made upon of three fatty acids and glycerol.
• what are proteins made up of?


  long chains of small units called amino acids.
• what is a catalyst and what are enzymes?

  1. catalysts increase the rate of a chemical reaction without changing chemically themselves.
  2. enzymes are biological catalysts (proteins) and catalyse specific reactions due to the shape of their active site - lock and key theory.
• enzymes, substrates and products


  1. lipase is the enzyme that breaks down lipids (substrate) into three fatty acids and glycerol
  2. amylase is the enzyme that breaks down starch (substrate) into the product of glucose
  3. protease is the enzyme that breaks down proteins (substrate) into amino acids
  4. pepsin is an enzyme that breaks down proteins into amino acids
• what happens when enzymes denature?


  1. enzymes are denatured at high temperatures
  2. the active site changes shape and the substrate no longer fits in
  3. no reaction occurs and products are not made
• what is the function of the mouth in the digestive system?


  1. teeth break up food to increase SA.
  2. saliva contains amylase to begin carbohydrate digestion
• what is the function of the gall bladder indigestion?


  stores bile from liver which enters the small intestine via the bile duct where it neutralises stomach acid and emulsifies fats.
• what is metabolism?


  the sum of all the chemical reactions in the body
• examples of metabolic reactions


  1. building large molecules from lots of smaller ones - glycogen from glucose
  2. changing one molecule into another - glucose to fructose
  3. breaking down larger molecules into smaller ones - proteins into amino acids
• what are factors affecting enzyme action?


  Temperature

  pH

  substrate concentration

  enzyme concentration
• how does temperature affect enzyme action?


  1. as temperature increases, so does the rate of enzyme activity.
  2. an optimum activity is reached at the optimum temperature.
  3. however, a continued increase in temperature will result in a sharp decrease in enzyme activity as the active site changes shape - denatures.
• how does pH affect enzyme action?


  1. as temperature increases, so does the rate of enzyme activity.
  2. an optimum activity is reached at the optimum temperature.
  3. however, a continued increase in temperature will result in a sharp decrease in enzyme activity as the active site changes shape - denatures.
• what is the lock and key theory ?

  • every enzyme has an active site with a unique shape that fits onto the substrate involved in a reaction
  • enzymes will catalyse the breakdown of the substrate
  • products are released from the active site
  • the enzyme molecule is unchanged and can be reused