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Enzymes

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Enzymes Enzymes Presentation Transcript

  • Enzymes
    By: Chen Dewei (2P304)
  • Introduction of Enzymes
    Biological catalysts which speed up biological reactions by lowering the activation energy required for them to take place
    Mostly made up of proteins
    Not used up or chemically changed at the end of the biological reaction
  • Introduction of Enzymes (Cont.)
    Can be used again and again
    Produced only when needed
    Catalyse reversible reactions
    E + S ⇌ ES -> EP ⇌ E + P (E= Enzyme, S= Substrate, P=Product)
  • Enzyme-Catalysed Reactions
    Anabolic reactions
    Synthesis of simpler substances into complex ones
    Amino acids -> Polypeptides -> Proteins
    Catabolic reactions
    Breakdown of complex substances into simpler ones
    Hydrogen peroxide -> Oxygen + Water
    2H2O2-> O2 + 2H2O
    To prevent the poisonous effect of hydrogen peroxide
  • Classification of Enzymes
    Hydrolases (Hydrolysis)
    Catalyse hydrolytic reactions in the body (eg. Of digestion)
    Oxidoreductoases (Oxidation – Reduction)
    Transferases (Transfer groups of atoms)
    Lyases (Add/Remove atoms to/from a double bond)
    Isomerases (Rearrange atoms)
    Ligases (Combine molecules using ATP)
  • Types of Hydrolases
    Carbohydrases
    Digest carbohydrates
    Amylase (starch)
    Maltase (maltose)
    Sucrase (sucrose)
    Proteases
    Digest proteins
    Pepsin
    Erepsin
    Lipases
    Digest fats
    Lipase
  • Characteristics of Enzymes
    Speed up chemical reactions
    Small amount is needed to catalyse a reaction because enzymes can be used again and again
    The shapes of the active sites make enzymes highly specific, meaning they can only interact with 1 type of substrate to form an enzyme-substrate complex
    Presented using the ‘lock and key’ hypothesis
  • “Lock and Key” Hypothesis
    The active site of an enzyme molecule = lock; substrate molecule that the enzyme acts on = key
    When the enzyme and substrate molecules are bound together, they form an enzyme-substrate complex
    Substrate molecule is subsequently converted into products
    Product molecules leave the active site
    Enzyme molecule is free to bind with more substrate molecules
  • “Induced Fit” Model
    Enzyme molecule can undergo adjustments at its active site
    Binds more tightly with substrate molecule
    Facilitates binding at active site and speeds up rate of chemical reaction
  • Temperature
    pH
    Concentrations of substrates in enzymatic reactions
    Factors Which Affect Enzyme Activity
  • Temperature
    Optimum temperature – the temperature at which an enzyme is the most active (can catalyse the most number of reactions per second)
    Rise in temperature (till optimum) -> Increase in enzyme activity
    Kinetic energy of particles increases
    Increases the chance of substrate molecules fitting into the active sites of enzyme molecules
    More rapid formation of enzyme-substrate complexes
    Increase in formation of products
  • Temperature (Cont.)
    When temperature exceeds the optimum temperature of enzyme activity, it starts to fall rapidly
    H-H bonds in enzymes break, leading to the denaturation of enzymes
    Unique 3-dimensional structure lost
    Denaturation is irreversible
  • pH
    Optimum pH = maximum activity
    Most enzymes lose their abilities to catalyse reactions at pH 3 and 11
    Extreme changes in pH of a solution will denature the enzyme, just like temperature
  • pH (cont.)
    Slight changes in pH is enough to change the electrostatic charges of the active site of enzyme and substrate
    Electrostatic repulsion occurs
    Inhibits the formation of enzyme-substrate complex
  • Substrate and Enzyme Concentrations
    Substrate concentration increases -> rate of reaction increases
    Saturation of enzyme molecules (all being made use of)
    Reaction cannot take place
    Increase in enzyme concentration will increase the rate of reaction again
  • Coenzymes
    Not made up of protein (unlike enzymes)
    Organic compounds
    Bind with enzymes before the latter can catalyse reactions
  • References
    http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/Enzymes.html
    http://www.elmhurst.edu/~chm/vchembook/570enzymes.html
    http://www.mrothery.co.uk/studentswork/student%20presentations/Enzyme%20Activity.ppt
  • End of Presentation