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    Enzymes and Reactions

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    techninja256

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    Enzymes and Reactions

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    techninja256
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    Original Title

    Enzymes and Reactions (3)

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    4 views5 pages

    Enzymes and Reactions

    Uploaded by

    techninja256

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    © All Rights Reserved
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    of 5

    Enzymes and reactions

     Many chemical reactions can be speeded up by substances called catalysts.


     Enzymes are proteins that act as biological catalysts.
     A catalyst is a substance which speeds up the rate of reaction in chemical reactions, without being
    used up.
     The enzyme is not changed by the reaction and so can be used repeatedly.
     Most enzyme names end in –ase, e.g. lipase, protease.
     Some enzymes help to build up molecules or synthesis them.
    Eg.

    Enzyme action: - 'Lock and key' Hypothesis

     Enzymes are very specific, each kind of enzyme catalyse one kind of reaction only.
     To catalyse a reaction, enzyme molecule and substrate molecule need to meet and joint together by a
    temporary bond.
     All enzymes contain an active site, which is a sequence of amino acids with a specific shape.
     This shape is complementary to the substrate.
     When the enzyme breaks the substrate down, the substrate enters the active site to form an
    enzyme-substrate complex.
     The substrate is broken down and the product is released.
     Each enzyme is complementary to only one type of substrate; hence it cannot break down other
    substrates.
     For example, proteases break down proteins so that amino acids can be absorbed into the blood.
     Proteases cannot, however, break down other molecules such as carbohydrates, which can only be
    broken down by carbohydrase enzymes.

    1
     The starch is split into maltose molecules.
     The enzyme is unaltered, and ready to accept another part of the starch molecule

    2
    Factors affecting the rate of enzymes

    1 Temperature
    2 pH
    The activity of enzymes is affected by temperature and pH

    1. Effect of temperature on enzymes


    o The optimum (best) temperature for enzyme-controlled reactions is 370C (body temperature).
    o As the temperature increases, the rate of reaction increases.
    o But at very high temperatures the enzymes denature.
    o The enzyme activity gradually increases with temperature up to around 37ºC, or body temperature.
    o Then, as the temperature continues to rise, the rate of reaction falls rapidly as heat energy denatures
    the enzyme.
    o Most enzymes are denatured above 400C.
     The graph shows the typical change in an enzyme's activity with increasing temperature.

    3
    2. Effect of pH on enzymes
    o The pH of a solution is how acidic or alkaline it is.
    o Different enzymes work best at different pH values.
    o The optimum pH for an enzyme depends on where it normally works.
    o It is around neutral (pH= 7) for most enzymes but there are some exceptions.

    o Changes in pH also alter an enzyme’s shape and slow down its activity, but this can usually be reversed
    if the optimum pH is restored.
    o An extreme pH can denature enzymes – the active site is deformed permanently.

    o Extremes of pH cause enzyme molecules to lose their shape, so they no longer bind with their
    substrate.

    4
    In seeds…
    o Amylase is found in seeds. When the seed begins to germinate, the amylase is activated and catalyses
    the breakdown of insoluble starch to soluble maltose in the seed. The maltose is used by the growing
    embryo as an energy source and to make cellulose for new cell walls.

    Uses of enzymes
    1 Biological washing powders contain enzymes, often obtained from microorganisms such as bacteria or
    fungi.
    o The enzymes break down proteins or fats on the fabric/cloths, forming water soluble substances that
    can be washed away.
    2 Pectinase is used to break down cell walls in fruits, making it easier to extract juice from them.
    2 The antibiotic penicillin is made by cultivating the fungus Penicillium in a fermenter. The fermenter is
    kept at the correct pH and temperature for the enzymes of the fungus to work well.

    Activity 1 pg 9
    Activity 2 pg 11

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