Enzymes

• Enzymes


  Biological catalysts made up of protein that alter the rate of chemical reactions without themselves being chemically changed at the end of the reaction
• Metabolism


  The total chemical reactions occurring inside a cell
• Types of metabolism


  • Anabolism - Processes that build up simple molecules into complex compounds, requiring energy
  • Catabolism - Processes that break down complex compounds into simpler ones, releasing energy
• Hydrolases


  Enzymes that catalyze hydrolytic reactions
• Types of hydrolases


  • Carbohydrases - Digest carbohydrates (e.g. salivary amylase, pancreatic amylase)
  • Proteases - Digest proteins (e.g. pepsin)
  • Lipases - Digest fats (e.g. lipase in pancreatic juice)
• Substrate


  The substances on which enzymes act
• Enzyme specificity


  • Enzymes have a specific shape with an active site that can only bind to substrates with a complementary shape
  • Enzyme-substrate complex forms when substrate binds to active site
  • Substrate is converted to products, which then leave the enzyme unchanged
• Lock and key hypothesis

  The enzyme is the lock and the substrate is the key
• Induced-fit theory


  The active site of enzymes is flexible, and changes shape to fit the substrate exactly when it binds
• Characteristics of enzymes


  • Speed up chemical reactions by decreasing activation energy
  • Affected by pH - each has an optimum pH
  • Required in small amounts as they are not consumed
  • Highly specific in their action
  • Can catalyze reversible reactions
  • Affected by temperature - have an optimum temperature
• As temperature increases


  Enzyme activity increases due to increased molecular collisions and formation of enzyme-substrate complex
• At high temperatures


  Enzyme activity decreases due to denaturation of the enzyme protein
• Importance of enzymes


  • In biological washing powders (e.g. protease, lipase)
  • In food industry (e.g. pectinase, amylase)
  • In seed germination (digest stored food)
  • In biosensors (e.g. glucose biosensor)
• Enzymes


  Decrease the activation energy of the reaction and therefore speed up the rate of reaction
• Enzyme catalysis


  1. Activation energy without enzyme

  2. Activation energy with enzyme

  3. Substrate

  4. Product
• Enzymes


  • Needed in small amounts
  • Catalyse reversible reactions
  • Protein in nature
• Temperature above the optimum temperature


  Affects enzyme reactions, enzymes lose their shape and configuration and are said to be denatured
• Extreme pH


  Affects enzyme reactions, enzymes lose their shape and configuration and are said to be denatured
• Effect of temperature on the rate of enzyme reaction

  1. Increased enzyme activity

  2. Enzymes are inactive

  3. Enzymes are denatured
• Optimum temperature


  Temperature at which there is maximum rate of reaction
• Effect of pH on rate of enzyme reaction

  1. Enzymes work best at optimum pH

  2. Activity decreases when on either side of optimum pH

  3. Extreme pH denatures enzymes
• Increasing enzyme concentration


  Rate of reaction increases
• Increasing substrate concentration


  Rate of reaction increases until enzyme active sites are saturated, then remains constant
• A limiting factor is one which is present in the lowest concentration and directly affects the rate of reaction if its quantity is changed
• Enzyme catalysed reaction - Catalase

  1. Hydrogen peroxide placed in test tube

  2. Fresh liver added

  3. Boiled liver added as control

  4. Fresh liver releases oxygen, boiled liver does not
• Liver contains catalase which breaks down hydrogen peroxide to water and oxygen
• Boiling the liver has denatured the enzyme catalase, so no bubbles were formed