digestion

• digestion system


  breaks down insoluble molecules into small, soluble molecules
• carbohydrates


  chemical elements of carbon, hydrogen and oxygen

  used for energy
• simple carbohydrates


  glucose
• complex carbohydrates 


  starch and cellulose
• lipids


  fats and oils

  is an energy store

  important in cell membranes as hormones

  soluble in water
• proteins


  made up of amino acids

  they are coiled up so other molecules can fit into proteins

  if temperature gets too hot - enzyme denature
• what do proteins act up as

  • structural components of tissues such as muscles and tendons
  • hormones such as insulin
  • antibodies
  • enzymes
• enzymes


  they control in body chemical reactions

  active site = 'dent'

  involved in:

  • building large molecules from lots of small molecules
  • changing one molecule into another
  • breaking down a large molecule into smaller one
• how do enzymes work

  the reactant (substrate) fits in the active site

  then enzyme and substate bind together

  reaction then happens rapidly
• factors of biological reactions

  • temperature
  • concentration
  • surface area
• temperature 


  reactions in cells happen at a low temp.

  the rate of enzyme controlled reactions increases as temperature increases

  but one temp is really high (around 40), enzymes start to denature (amnio acids start to unravel) and change the shape of the active site
• pH


  this changes the affects the forces holding the active site

  different enzymes work at different pH levels

  however a change in pH can mean that the enzyme will stop working
• digestive enzymes


  these are produced by specialised cells in glands and in lining of the gut (the gut is hollow and muscular)

  they are passed out into the gut and comes into contact with the food molecules and break them down
• digestive system


  starts with mouth - ends with anus

  made up of different organs and glands

  stomach and small intestine is mainly where food is digested
• digesting carbohydrates


  carbohydrases = enzymes that break down carbohydrates

  starch is broken down by amylase (type of enzyme)
• amylase


  it is produced in salivary gland (where the breaking down starts) + pancreas (digestion doesn't happen here) + small intestine
• digesting proteins


  breaking down catalysed by protease enzymes

  protease - produced by stomach, pancreas, small intestine

  amino acid break down - stomach + small intestine
• digesting fats


  broken down in small intestine - catalysed by lipase enzyme (made in pancreas (moved to small intestine) and small intestine)
• stomach


  stomach protease works best in acidic pH

  so it produces concentrated solution of hydrochloric acid from the same glands - kills the majority of bacteria

  has a thick layer of mucus which protects stomach walls from being digested by the acid and enzymes
• small intestine


  works best in an alkaline environment

  to change the acidic liquid from stomach into alkali - the liver produces and releases bile (stored in gallbladder) to neutralise the acid

  bile is squired from bile duct

  has both active transport and diffusion

  it absorbs food molecules into the blood, the muscular walls squeeze out the excess into large intestine (where water is absorbed into blood)
• diffusion in small intestine

  lined with villi - increasing surface area = more room for diffusion

  lining has good blood supply - so its straight away carried away which keeps the steep concentration gradient
• active transport in small intestine

  these digested food molecules move against the concentration gradient
• surface area


  bile - emulsifies fats in food = physically breaks ups large drops of fat into smaller drops

  which provides a larger surface area of fats for lipase enzymes to break down

  larger surface area = quicker the break down
• uses of enzymes (not inside body)

  detergents

  baby foods

  sugar syrup

  • it helps use less energy on making things - uses less money on energy
  • but you need to control temp. and pH - costs lots of money to control this