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ENZYMES
LEARNING GOALS

 Describe the role of enzymes and why they are
  essential to living organisms
 List the factors that may affect the rate of an
  enzyme catalysed reaction
 Describe the importance of the structure of an
  enzyme to its functioning
ENZYMES
Enzymes are molecules that act as catalysts
to speed up biological reactions.

The compound on which an enzyme acts is
the substrate.

Enzymes can break a single structure into
smaller components or join two or more
substrate molecules together.

Most enzymes are proteins.


       Many fruits contain enzymes that are used in commercial
       processes. Pineapple (Ananas comosus, right) contains the
       enzyme papain which is used in meat tenderization processes and
       also medically as an anti-inflammatory agent.
ENZYMES
ENZYME EXAMPLES
                                  Enzyme                  Role

                                                Stomach enzyme used to
                                                 break protein down into
                                   Pepsin
                                              peptides. Works at very acidic
                                                        pH (1.5).

                                              Digestive enzymes which act
                                  Proteases    on proteins in the digestive
                                                         system


                                               A family of enzymes which
                                  Amylases     assist in the breakdown of
                                                      carbohydrates


                                               A family of enzymes which
3D molecular structures for the    Lipases
  enzymes pepsin (top) and                          breakdown lipids
   hyaluronidase (bottom).
ENZYME EXAMPLES
   One of the fastest enzymes in the body is
    catalase. Catalase breaks down hydrogen
    peroxide, a waste product of cell metabolism, into
    water and oxygen. Accumulation of hydrogen
    peroxide is toxic so this enzyme performs an
    important job in the body.
ENZYME POWER!
   All reactants need to have a certain energy before
    they will react. This is like an energy barrier that
    it has to overcome before a reaction will occur. It
    is called the activation energy.

   Enzymes are organic catalysts.

   All catalysts lower the energy barrier, allowing
    the reactants (substrates) to react faster forming
    the products.

   Enzymes do not participate in the reaction.
Finish
ENZYMES




                   Without enzyme: The activation
                   energy required is high.




                                   Direction of reaction
      Reactant     With enzyme: The activation
                   energy required is lower.
     High energy


                        Product


                       Low energy




                          Start
ENZYMES
 Enzymes have a specific region
 where the substrate binds and
 where catalysis occurs. This is
 called the active site.

 Enzymes are substrate-specific,
 although specificity varies from
 enzyme to enzyme.

 When a substrate binds to an
 enzyme’s active site, an enzyme-   Space filling model of the yeast
                                    enzyme hexokinase. Its active
 substrate complex is formed.       site lies in the groove (arrowed)
molecules. It has three active sites (arrowed).
              Ribonuclease S, that breaks up RNA
             This model (above) is an enzyme called
                                                       Enzyme molecule:
                                                       The complexity of the
                                                       active site is what makes
                                                       each enzyme so specific
                                                       (i.e. precise in terms of the
Active site:                                           substrate it acts on).
The active site contains both binding
and catalytic regions. The substrate
is drawn to the enzyme’s surface and
the substrate molecule(s) are
positioned in a way to promote a
reaction: either joining two molecules                 the cleft of the enzyme.
together or splitting up a larger one.                 acts on. They are drawn into
                                                       chemicals that an enzyme
                                                       Substrate molecules are the
                                                       Substrate molecule:
                        ENZYME ACTIVE SITES
LOCK AND KEY MODEL
          The lock and key model of enzyme action, proposed earlier
          this century, proposed that the substrate was simply drawn into
          a closely matching cleft on the enzyme molecule.

                                                                       Products
              Substrate




            Symbolic representation of the lock and key model of enzyme action.
          1. A substrate is drawn into the active sites of the enzyme.
 Enzyme
          2. The substrate shape must be compatible with the enzymes active site in
             order to fit and be reacted upon.
          3. The enzyme modifies the substrate. In this instance the substrate is
             broken down, releasing two products.
INDUCED FIT MODEL
 More recent studies have             Two substrate
                                      molecules are
 revealed that the process is         drawn into the
 much more likely to involve          cleft of the
                                      enzyme.
 an induced fit.
                                      The enzyme
     The enzyme or the reactants      changes shape,
     (substrate) change their shape   forcing the substrate
     slightly.                        molecules to
                                      combine.

     The reactants become bound to
     enzymes by weak chemical
     bonds.

     This binding can weaken bonds    The resulting end
     within the reactants             product is released
                                      by the enzyme
     themselves, allowing the
                                      which returns to its
     reaction to proceed more         normal shape, ready
     readily.                         to undergo more
                                      reactions.
CHANGING THE ACTIVE SITE
   Changes to the shape of the active site will result in a
    loss of function. Enzymes are sensitive to various
    factors such as temperature & pH.




   When an enzyme has lost its characteristic 3D shape, it
    is said to be denatured. Some enzymes can regain
    their shape while in others, the changes are
    irreversible.
THE EFFECT OF TEMPERATURE ON
ENZYME ACTION                      Speeds up all reactions,
                                    but the rate of
      Optimum                       denaturation of enzymes
    Temperature                     also increases at higher
     for enzyme   Too hot for       temperatures.
                  Enzyme to
                     work
                                   High temperatures break
                                    the disulphide bonds
                                    holding the tertiary
  Too cold                          structure of the enzyme
for Enzyme                          together thus changing the
   to work                          shape of the enzyme.

                                   This destroys the active
                                    sites & therefore makes
                                    the enzyme non –
                                    functional.
THE EFFECT OF TEMPERATURE ON
    ENZYME ACTION




   The curve in the blue represents an enzyme isolated from an
    organism living in the artic. These cold dwelling organisms are called
    psychrophiles.

   The curve in red represents an enzyme isolated from the digestive
    tract of humans.

   The curve in green represents an enzyme isolated from a thermophile
    bacteria found growing in geothermal sea beds.
THE EFFECT OF PH ON ENZYME
ACTION
                  Like all proteins, enzymes are
                   denatured by extremes of pH
                   (acidity/alkalinity).

                  The green curve is for pepsin
                   that digests proteins in the
                   stomach.

                  The red curve represents the
                   activity of arginase that breaks
                   down arginine to ornithine &
                   urea in the liver.
THE EFFECT OF ENZYME
CONCENTRATION ON ENZYME
ACTION
             Assuming   that the
             amount of substrate
             is not limiting, an
             increase in enzyme
             concentration causes
             an increase in the
             reaction rate.
THE EFFECT OF SUBSTRATE
CONCENTRATION ON ENZYME
ACTION
              Assuming that the amount of
               enzyme is constant, an increase in
               substrate concentration causes a
               diminishing increase in the
               reaction rate.

              A maximum rate is obtained at a
               certain concentration of substrate
               when all enzymes are occupied
               substrate (the rate cannot
               increase any further).
THE EFFECT OF COFACTORS ON
ENZYME ACTION
              Cofactors are substances that
               are essential to the catalytic
               activity of some enzymes.
              Cofactors may alter the shape
               of enzymes slightly to make
               the active sites functional or
               to complete the reactive site.
              Enzyme cofactors include
               coenzymes (organic
               molecules) or activating ions
               (eg. Na+, K+..)
              Vitamins are often coenzymes
               (eg. Vit B1, Vit B6…)
THE NATURE OF ENZYME
 INHIBITORS
 Enzyme   inhibitors may or may not act reversibly:

 Reversible: the inhibitor is temporarily bound to
 the enzyme, thereby preventing its function (used
 as a mechanism to control enzyme activity).

 Irreversible:the inhibitor may bind permanently
 to the enzyme causing it to be permanently
 deactivated.
THE NATURE OF ENZYME
INHIBITORS
 Reversible   Enzymes work in one of two ways:

 Competitive   inhibitors: the inhibitor competes
 with the substrate for the active site, thereby
 blocking it and preventing attachment of the
 substrate.

 Non-competitive:     the inhibitor binds to the
 enzyme (but not at the active site) and alters its
 shape. It markedly slows down the reaction rate
 by making the enzyme less able to perform its
 function (allosteric inhibition).
SUMMARY: ENZYMES
1.   Enzymes work very rapidly and help to speed
     up biological reactions.
2.   Enzymes can be used multiple times (however
     they do degrade eventually).
3.   Enzymes can work in both directions of a
     chemical reaction.
4.   Enzymes have optimal temperatures and pH
     that they will operate. Beyond these optimum
     ranges they will either not work or become
     denatured (unfolded/breakdown).
5.   Enzymes are usually specific to one particular
     substrate.

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Enzymes

  • 2. LEARNING GOALS  Describe the role of enzymes and why they are essential to living organisms  List the factors that may affect the rate of an enzyme catalysed reaction  Describe the importance of the structure of an enzyme to its functioning
  • 3. ENZYMES Enzymes are molecules that act as catalysts to speed up biological reactions. The compound on which an enzyme acts is the substrate. Enzymes can break a single structure into smaller components or join two or more substrate molecules together. Most enzymes are proteins. Many fruits contain enzymes that are used in commercial processes. Pineapple (Ananas comosus, right) contains the enzyme papain which is used in meat tenderization processes and also medically as an anti-inflammatory agent.
  • 5. ENZYME EXAMPLES Enzyme Role Stomach enzyme used to break protein down into Pepsin peptides. Works at very acidic pH (1.5). Digestive enzymes which act Proteases on proteins in the digestive system A family of enzymes which Amylases assist in the breakdown of carbohydrates A family of enzymes which 3D molecular structures for the Lipases enzymes pepsin (top) and breakdown lipids hyaluronidase (bottom).
  • 6. ENZYME EXAMPLES  One of the fastest enzymes in the body is catalase. Catalase breaks down hydrogen peroxide, a waste product of cell metabolism, into water and oxygen. Accumulation of hydrogen peroxide is toxic so this enzyme performs an important job in the body.
  • 7. ENZYME POWER!  All reactants need to have a certain energy before they will react. This is like an energy barrier that it has to overcome before a reaction will occur. It is called the activation energy.  Enzymes are organic catalysts.  All catalysts lower the energy barrier, allowing the reactants (substrates) to react faster forming the products.  Enzymes do not participate in the reaction.
  • 8. Finish ENZYMES Without enzyme: The activation energy required is high. Direction of reaction Reactant With enzyme: The activation energy required is lower. High energy Product Low energy Start
  • 9. ENZYMES Enzymes have a specific region where the substrate binds and where catalysis occurs. This is called the active site. Enzymes are substrate-specific, although specificity varies from enzyme to enzyme. When a substrate binds to an enzyme’s active site, an enzyme- Space filling model of the yeast enzyme hexokinase. Its active substrate complex is formed. site lies in the groove (arrowed)
  • 10. molecules. It has three active sites (arrowed). Ribonuclease S, that breaks up RNA This model (above) is an enzyme called Enzyme molecule: The complexity of the active site is what makes each enzyme so specific (i.e. precise in terms of the Active site: substrate it acts on). The active site contains both binding and catalytic regions. The substrate is drawn to the enzyme’s surface and the substrate molecule(s) are positioned in a way to promote a reaction: either joining two molecules the cleft of the enzyme. together or splitting up a larger one. acts on. They are drawn into chemicals that an enzyme Substrate molecules are the Substrate molecule: ENZYME ACTIVE SITES
  • 11. LOCK AND KEY MODEL The lock and key model of enzyme action, proposed earlier this century, proposed that the substrate was simply drawn into a closely matching cleft on the enzyme molecule. Products Substrate Symbolic representation of the lock and key model of enzyme action. 1. A substrate is drawn into the active sites of the enzyme. Enzyme 2. The substrate shape must be compatible with the enzymes active site in order to fit and be reacted upon. 3. The enzyme modifies the substrate. In this instance the substrate is broken down, releasing two products.
  • 12. INDUCED FIT MODEL More recent studies have Two substrate molecules are revealed that the process is drawn into the much more likely to involve cleft of the enzyme. an induced fit. The enzyme The enzyme or the reactants changes shape, (substrate) change their shape forcing the substrate slightly. molecules to combine. The reactants become bound to enzymes by weak chemical bonds. This binding can weaken bonds The resulting end within the reactants product is released by the enzyme themselves, allowing the which returns to its reaction to proceed more normal shape, ready readily. to undergo more reactions.
  • 13. CHANGING THE ACTIVE SITE  Changes to the shape of the active site will result in a loss of function. Enzymes are sensitive to various factors such as temperature & pH.  When an enzyme has lost its characteristic 3D shape, it is said to be denatured. Some enzymes can regain their shape while in others, the changes are irreversible.
  • 14. THE EFFECT OF TEMPERATURE ON ENZYME ACTION  Speeds up all reactions, but the rate of Optimum denaturation of enzymes Temperature also increases at higher for enzyme Too hot for temperatures. Enzyme to work  High temperatures break the disulphide bonds holding the tertiary Too cold structure of the enzyme for Enzyme together thus changing the to work shape of the enzyme.  This destroys the active sites & therefore makes the enzyme non – functional.
  • 15. THE EFFECT OF TEMPERATURE ON ENZYME ACTION  The curve in the blue represents an enzyme isolated from an organism living in the artic. These cold dwelling organisms are called psychrophiles.  The curve in red represents an enzyme isolated from the digestive tract of humans.  The curve in green represents an enzyme isolated from a thermophile bacteria found growing in geothermal sea beds.
  • 16. THE EFFECT OF PH ON ENZYME ACTION  Like all proteins, enzymes are denatured by extremes of pH (acidity/alkalinity).  The green curve is for pepsin that digests proteins in the stomach.  The red curve represents the activity of arginase that breaks down arginine to ornithine & urea in the liver.
  • 17. THE EFFECT OF ENZYME CONCENTRATION ON ENZYME ACTION  Assuming that the amount of substrate is not limiting, an increase in enzyme concentration causes an increase in the reaction rate.
  • 18. THE EFFECT OF SUBSTRATE CONCENTRATION ON ENZYME ACTION  Assuming that the amount of enzyme is constant, an increase in substrate concentration causes a diminishing increase in the reaction rate.  A maximum rate is obtained at a certain concentration of substrate when all enzymes are occupied substrate (the rate cannot increase any further).
  • 19. THE EFFECT OF COFACTORS ON ENZYME ACTION  Cofactors are substances that are essential to the catalytic activity of some enzymes.  Cofactors may alter the shape of enzymes slightly to make the active sites functional or to complete the reactive site.  Enzyme cofactors include coenzymes (organic molecules) or activating ions (eg. Na+, K+..)  Vitamins are often coenzymes (eg. Vit B1, Vit B6…)
  • 20. THE NATURE OF ENZYME INHIBITORS  Enzyme inhibitors may or may not act reversibly:  Reversible: the inhibitor is temporarily bound to the enzyme, thereby preventing its function (used as a mechanism to control enzyme activity).  Irreversible:the inhibitor may bind permanently to the enzyme causing it to be permanently deactivated.
  • 21. THE NATURE OF ENZYME INHIBITORS  Reversible Enzymes work in one of two ways:  Competitive inhibitors: the inhibitor competes with the substrate for the active site, thereby blocking it and preventing attachment of the substrate.  Non-competitive: the inhibitor binds to the enzyme (but not at the active site) and alters its shape. It markedly slows down the reaction rate by making the enzyme less able to perform its function (allosteric inhibition).
  • 22. SUMMARY: ENZYMES 1. Enzymes work very rapidly and help to speed up biological reactions. 2. Enzymes can be used multiple times (however they do degrade eventually). 3. Enzymes can work in both directions of a chemical reaction. 4. Enzymes have optimal temperatures and pH that they will operate. Beyond these optimum ranges they will either not work or become denatured (unfolded/breakdown). 5. Enzymes are usually specific to one particular substrate.