the human digestive system

• Enzymes


  Biological catalysts
• Catalyst


  A substance which increases the rate of reaction without being used up itself
• Lock and key model of enzymes

  The enzyme and the substrate fit together like a lock that fits a key. this would lower the energy of activation so that the product can form more easily.

  The active site is complementary and specific to the substracte

  
• Induced fit


  The change in shape of the active site of an enzyme so that it binds more tightly to the substrate, induced by entry of the substrate. (More realistic)
• Enzyme activity/RoR as temp increases

  Low: Less active

  Increasing to optimum: rate of reaction increases

  Too hot: Enzymes denature and RoR falls

  
• Enzymes denaturing


  first tip remember they are a protein

  -kinetic energy reference

  -breaking the H bonds between the amino acids

  -changing the shape of the active site

  - so fewer enzyme substrate complexes form
• Enzyme activity as pH increases

  Too high or low, pH interferes with bonds holding enzymes together (active site changes shape)

  
• Investigating effect of pH on Enzyme activity


  1) Put a drop of iodine solution into every well of the spotting tile.

  2) Place a Bunsen burner on a heat-proof mat and a tripod and gauze over until it is 35C

  3) Use a syringe to the 1cm3 of amylase solution and 1cm3 of a buffer solution with a pH of 5 to a boiling tube.

  4) Next, use a different syringe to add 5cm3 of a starch solution to the boiling tube

  5) Immediately mix the contents of the boiling tube and start a stop clock

  6) Use continuous sampling to record how long it takes for the amylase

  7) When the iodine solution goes brown/orange, starch is no longer present.
• Calculating rate of reaction

  Rate=1000/time
• Digestive enzymes


  - Amylase

  - Protease

  - Lipases
• Amylase


  Break down carbohydrates/starch into maltose and other simplesugars

  Made in:

  - Salivary glands

  - Pancreas

  - Small intestine
• Proteases


  Breaks down proteins into amino acids

  Made in:

  - Stomach (its called pepsin there)

  - Pancreas

  - Small intestine
• Lipases


  Break down lipids into glycerol and fatty acids

  Made in:

  - Pancreas

  - Small intetsine
• Bile


  A substance produced by the liver and stored in the gallbladder that breaks up fat particles.

  Smaller particles means there is a bigger surface area for lipase to work on, so, digestion is faster

  It also neutralises stomach acid ion the small intestine
• Salivary glands


  Produce amylase enzyme
• Liver


  Where bile is produced
• Stomach


  - Pummels food with its muscular walls

  - Produces protease enzyme, pepsin

  - Produces hydrochloride acid to kill bacteria and give the right pH for protease enzyme
• Gallbladder


  Where bile is stored before being released into the small intestine
• Pancreas


  Produces protease, amylase and lipase which are released into small intestine
• Small intestine


  Where digested food/nutrients is absorbed into the blood
• Large intestine


  Where excess water is absorbed from food
• Rectum


  Where faeces (made up of mostly indigestible food) is stored before being excreted through the anus
• Preparing a food sample

  1. Break up a piece of food using a pestle and mortar

  2. Transfer the ground up food to a beaker

  3. Add distilled water and stir with a glass rod

  4. When some of the food is dissolved filter the solution using a funnel lined with filter paper in order to get rid of solid bits of food
• Testing for sugars


  Benedict's test

  1. Prepares a food sample and transfer 5cm3 to a test tube

  2. Prepare a water bath and set to 75 degrees C

  3. Add about 10 drops of Benedict's solution to the test tube using a pipette

  4. Place test tube in water bath for 5 mind

  5. If sugars are present, colour will change from blue, green, yellow and brick-red.
• Testing for starch


  Iodine solution changes from orange to blue-black in the presence of starch
• Testing for proteins


  Biuret test

  1. Prepare a food sample and transfer 2cm3 top a test tube

  2. Add 2cm3 of Beuret solution and mix content gently by shaking it

  3. If protein is present, colour will go from blue to purple/violet
• Sudan III test for lipids

  1. Prepare food sample (no need to filter) and transfer 5 cm3 into test tube

  2. add 3 drops of sudan III stain solution to test tube and gently shake

  3. Solution stains lipids

  4. If lipids are present mixture will separate into 2 layers and the top layer will be bright red
• Test for sugars

  Benedict's test

  positive result: blue to green, to yellow, to brick-red
• Test for starch

  Iodine solution

  orange to blue-black
• Test for proteins

  Biuret test

  blue to purple/violet
• Test for lipids

  Sudan (III)

  Mixture seperates into 2 layers and top layer will be bright red