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    Chapter 5 Enzymes

    Uploaded by

    Meiying Lee

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    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd

    Chapter 5 Enzymes

    Uploaded by

    Meiying Lee
    6 views26 pages

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    Chapter 5 enzymes

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    6 views26 pages

    Chapter 5 Enzymes

    Uploaded by

    Meiying Lee

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 26

    CHAPTER 5

    What are enzymes?

    • Enzymes are catalysts that speed up the rate of chemical reaction


    without itself being changed.
    • They are proteins and are biological catalysts
    • Enzymes are necessary to all of the living organisms as they help in
    maintaining the speed of all metabolic reactions
    • For example, without the presence of enzyme, the digestion process
    could take up to 2-3 weeks to digest a meal. But, with the help of an
    enzyme, it only takes around 3-4 hours to digest the food
    How do enzymes work?

    • Enzymes are specific to a particular substrate as each enzyme has a


    complementary shape to the substrate.
    Enzyme Specificity
    • Enzymes are specific to one particular substrate as the active site of
    the enzyme is complementary to the substrate.
    • This is because enzyme is a protein and has a specific 3D shape
    • This is known as the lock and key hypothesis.
    Lock and Key Hypothesis
    Enzyme Specificity

    • Enzymes and substrates randomly move about in a solution


    • When an enzyme and its complementary substrate randomly collide-
    with the substrate fitting into the active site of the enzyme, an
    enzyme-substrate complex forms.
    • The products formed are then released from the active site. The
    enzyme is unchanged and will go on to catalyse further reactions.
    Effect of Temperature on Enzyme Function

    • Enzymes are proteins and have a specific shape, held by bonds


    • Enzymes work fastest at their optimum temperature which is 37
    degree.
    • Heating to high temperatures will break the bonds that hold the
    enzyme together and it will lose its shape – denaturation.
    • Substrates cannot fit into denatured enzymes as the shape of their
    active site has been lost
    • Denaturation is irreversible
    • Increasing the temperature from 0ºC to the optimum temp increases the activity
    of enzymes as the more energy the molecules have, the faster they move, hence,
    number of collisions with the substrate molecules increases, leading to a faster
    rate of reaction.
    Effect of pH on Enzyme Function
    • The optimum pH for most enzymes is 7 but some have lower
    optimum pH (pH 2),pepsin and some have a higher optimum pH ( 8 or
    9), amylase.
    • If the pH is not optimum, the bonds that hold the amino acid chain
    together to make up the protein can be destroyed.
    • This will change the shape of the active site, and substrate can no
    longer fit into it.
    • Moving too far away from the optimum pH will cause enzyme to
    denature.
    Activators and inhibitors
    • Activators make this binding more likely – for example, chloride ions are
    essential for the activity of salivary amylase.
    • Inhibitors make it more difficult for the enzyme to bind to the substrate – for
    example, cyanide ions block the active sites of enzymes involved in respiration.
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