04- enzymes

• enzymes

  • enzymes: proteins that function as biological catalysts. they catalyse or speed up chemical reactions and remain chemically unchanged at the end of the reaction
  • biological catalysts
  • catalyst: substance that can speed up a chemical reaction, without itself being chemically changes at the end of the reaction
  • enzymes lower activation energy required and speed up chemical reactions
  • activation energy: energy needed to start a chemical reaction
• enzymes are:

  • soluble in water
  • small enough to diffuse through cell membrane
  • involved in biological reactions
  • anabolic: reactions that build up/ synthesise complex molecules (e.g synthesis of proteins from amino acids)
  • catabolic: reactions that break down complex substances (e.g catalase breaks down hydrogen peroxide into oxygen and water)
• digestive enzymes:

  • amylase digests starch to maltose
  • maltase digests maltose to glucose
  • protease digests proteins to polypeptides to amino acids
  • lipase digests fats to fatty acids and glycerol
• classification of enzymes

  • carbohydrases are enzymes that digest carbohydrates
  • proteases are enzymes that digest proteins
  • Iipases are enzymes that digest fats (lipids)
• • enzyme specificity: each chemical reaction is catalysed by a unique enzyme
  • lock-and-key hypothesis
  • substrate: substance on which enzymes act (reactant)
  • active sites: grooves or pockets on the surface of an enzyme molecule in which the substrate molecule with the matching/ complementary shape can fit
  • 'lock' is enzyme, 'key' is substrate
  • when the substrate binds to the active site of an enzyme, and enzyme-substrate complex is formed
  • temporary molecule, reactions take place at the active site to convert substrate to product
• characteristics of enzymes

  • enzymes speed up chemical reactions
  • enzyme lower the activation energy
  • specific in action
  • only substrates with a complementary shape to the active site can fit into enzyme
  • required in minute amounts and remain unchanged at the end of reactions
  • same enzyme molecule can be used again
• Denaturation is the change in the three-dimensional structure of an enzyme or any other soluble protein, caused by heat or chemicals such as acids or alkalis
• characteristics of enzymes

  • enzymes are affected by pH
  • optimum pH
  • the pH condition vary from the optimum pH, the enzymes will start to denature

  
• characteristics of enzymes

  • enzymes are affected by temperature
  • An enzyme is less active at low temperatures : kinetic energy is low, rate of collision is very low
  • As the temperature increases, the rate of enzyme reaction increases : increasing kinetic energy of molecules, rate of effective collision is increased
  • optimum temperature, enzyme is most active
  • increasing the temperature above the optimum causes a rapid decrease in the rate of enzyme reaction : active site begins to lose its original shape, no longer complementary to substrate
  • All the enzyme molecules have been denatured

  
• characteristics of enzymes

  • enzymes are affected by substrate concentration
  • at low concentrations, enzyme occurs in excess
  • as substrate concentration increases, frequency of enzyme reaction increases, more enzyme-substrate complexes are formed, more products per unit time
  • limiting factor: substrate concentration
  • at high concentrations rate of reaction plateaus, all active sites of enzyme molecules are occupied (saturated)
  • limiting factor: enzyme concentration

  
• limiting factor: factor that affects the rate of reaction
• characteristics of enzymes

  • enzymes are affected by enzyme concentration
  • at low enzyme concentrations, rate of reaction increase as enzyme concentration increases : more active sites are available to bind with substrate molecules, frequency of effective collisions increases
  • limiting factor: enzyme concentration
  • as enzyme concentrations increase to higher concentrations, rate to reaction plateaus (maximum), there is an excess of enzyme molecules present and all substrate molecules are bound to an enzyme's active site and are engaged in reaction
  • limiting factor: substrate concentration

  
• enzymes:

  • speed up chemical reactions
  • specific in action
  • required in minute amounts and remains unchanged at the end pf the reaction
  • affected by temperature
  • affected by pH
  • affected by substrate concentration
  • affected by enzyme concentration