enzymes

• Role and function of enzymes:

  • Enzymes are BIOLOGICAL CATALYSTS—they speed up reactions without being consumed or altered.
  • ENZYMES are produced by living organisms to regulate chemical reactions.
• Structure of enzymes:

  • Enzymes are large PROTEINS composed of amino acid chains.
  • These proteins fold into UNIQUE SHAPES that are crucial for their function.
• LOCK AND KEY THEORY:

  • Each enzyme has an ACTIVE SITE (LOCK) with a shape that fits substances known as SUBSTRATES (KEY)
  • Enzymes are SPECIFIC which means one type of enzyme will only fit one type of substrate, (just like a lock and key).
  • When the substrate binds to the active site, it BREAKS UP to form the products
  • products released and enzyme is not changed
• Factors affecting enzyme activity:

  TEMPERATURE:

  • As you increase the temperature, the enzymes rate of reaction increases.
  • This is because the enzyme and substrates move around faster meaning increases kinetic enegry and MORE COLLISIONS per second.
  • The rate is the fastest at the OPTIMUM TEMPERATURE.
  • As the temperature increases past the optimum, the rate DECREASES. This is because the enzymes DENATURE causing the active site to change shape.
• pH affecting enzyme activity:

  • All enzymes have an OPTIMUM pH that they work the best in
  • As the pH increases or decreases from the optimum, the rate of reaction DECREASES. This is because enzymes DENATURE causing the active site to change shape.
  • Most enzymes in the human body have an optimum pH of 7, but there are some which have different ones.
• Breaking down nutrients:

  • DIGESTIVE ENZYMES are crucial in breaking down large molecules like STARCH, PROTEINS, and FATS into smaller, soluble molecules as they are too big to pass through the walls of the small intestine and be absorbed into the blood.
  • Digested molecules can be used to construct new carbohydrates, proteins and lipids in the body.
  • Some glucose produced by digestion is used for aerobic respiration.
• THREE types of digestive enzymes:

  • CARBOHYDRASES break down carbohydrates into simple sugars.
  • PROTEASES convert proteins into amino acids.
  • LIPASES break down lipids into glycerol and fatty acids.
• CARBOHYDRASES:

  • Break down carbohydrates into simple sugars.
  • Starch is a common carbohydrate in the human diet. It is made up of glucose molecules joined together.
  • Amylase is a carbohydrase that breaks down starch into maltose. 
  • Amylase digests starch in the mouth and small intestine. It is produced in the salivary glands, pancreas and small intestine.
• PROTEASES:

  • break down proteins into amino acids. 

  Proteins are digested in the stomach by pepsin and in the small intestine by other proteases.

  Proteases are produced in the stomach, pancreas and small intestine.
• Bile, produced by liver, stored in gall bladder and then released into the small intestine. Has 2 uses:

  • It is an alkaline substance so neutralises hydrochloric acid from the stomach, creates good conditions in small intestine so they can digest food quicker.
  • It emulsifies fats, breaks them into small droplets to create larger surface area for lipases to making digestion faster.
• Lipases


  • Digestive enzymes that break down lipids into glycerol and fatty acids, in the small intestine
  • Made in the pancreas and small intestine
• Required Practical

  1. Add iodine solution to each well of a spotting tile

  2. Set up a water bath at 35°C using a beaker of water and a thermometer for consistent temperature control during the experiment

  3. Combine 1 cm³ of amylase solution with 1 cm³ of a buffer solution with a pH of 5 in a test tube

  4. Place the tube in the water bath for five minutes using test tube holders

  5. Add 5 cm³ of starch solution to the amylase and buffer mixture and start timing the reaction using a stopwatch

  6. Every 30 seconds, use a dropping pipette to add a drop of the mixture to the iodine on the spotting tile

  7. Note the colour of the iodine

  8. Record when the iodine no longer turns blue-black, indicating starch breakdown

  9. Repeat with buffers of different pH values to see the effect of pH on amylase activity
• Understanding the results:

  • QUICKER the colour of the iodine solution stops turning BLUE-BLACK, the FASTER the rate of reaction, and the better the enzyme works.
  • The pH at which the iodine stops turning blue-black the FASTEST, OPTIMUM pH
  • If iodine remains BLUE-BLACK at a particular pH for the full amount of time, the amylase is assumed to have DENATURED, meaning the starch has NOT been broken down
  • Comparing rates across different pH levels will highlight the pH sensitivity of amylase.
  • CONTROLLED VARIABLES: fair test keep variables constant, such as amylase concentration and temperature.