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Enzymes. The controller of all CHEMICAL reactions in your body. Chemical Control (Enzymes).

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The controller of all CHEMICAL reactions in your body

chemical control enzymes
Chemical Control (Enzymes)

-at all times there are billions of chemical reactions taking place in any organism-all organisms therefore need to control these chemical reactions that make up metabolism-enzymes are the principal regulators of most chemical activity in living systems

- Enzymes control chemical reactions and therefore control Metabolism

There are over 2000 known enzymes, each of which is involved with one specific chemical reaction

  • Enzymes- enzymes are proteins- enzymes are referred to as organic catalysts
  • catalysts - inorganic or organic substance which speeds up the rate of a chemical reaction
    • Chemical reaction = Dehydration Synthesis and Hydrolysis
  • activation energy - the energy that must be overcome in order for a chemical reaction to occur.
    • Activation energy may otherwise be denoted as the minimum energy necessary for a specific chemical reaction to occur.
  • -- enzymes lower the energy needed to start a chemical rxn. (lower activation energy)


Activation Energy

transition state

(or activated complex)

bonds breaking

activation energy, Ea

bonds forming



Course of reaction

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Reaction profiles: uncatalysed and enzyme-catalysed

Uncatalysed reaction

Enzyme-catalysed reaction

Intermediate – formed between enzyme and one or more reactant molecules



Course of reaction

Click to see how an enzyme is involved in an enzyme-catalysed reaction

  • Structures of Enzymes- enzymes are large, complex proteinsProtein - all enzymes are either all protein or are protein with non-protein parts called coenzymes- coenzymes are often vitamins

Composition of Enzymes

  • apoenzyme -- protein part
  • coenzyme -- non-protein part attached to the main enzyme (usually a vitamin or a mineral)
  • holoenzyme -- complete functional enzyme (apoenzyme + coenzyme)
  • Enzymes are named according to the substrate they are specific to - substrates are the chemicals that each enzyme acts upon

Example of Naming:

  • The enzyme maltase (enzyme) breaks down (acts upon) the dissaccharide maltose (substrate) into 2 monosacchardies
  • The enzyme peptidase breaks the peptide bonds in proteins
  • - Usually enzymes end in – ase
active site or binding site
Active Site or Binding Site
  • Active Site or Binding Site -enzymes are usually much bigger than their substrates-the protein chains fold to make a three dimensional shape that has a specific pocket or site where the substrate can fit and interact-the specificity of the enzyme is dependent upon its active site




lock and key theory
“Lock and Key Theory”
  • "Lock and Key Theory" -- each enzyme is specific for one and ONLY one substrate (one lock - one key)
  • It is thought that, in order for an enzyme to affect the rate of a reaction, the following events must take place.
Enzyme Substrate Complex1. Enzyme forms a temporary association with the substrate or substrates2. The Enzyme and Substrate form a close physical association between the molecules called an enzyme substrate complex3. While the enzyme substrate complex is formed, the enzyme action takes place and the substrate is broken down into its smaller, simpler parts (Example: a dissacharide becomes 2 monosaccharide or 2 monosacchardies become a disaccharde)

4. After completion, the enzyme and the products separate. The enzyme is then ready to react with another substrate.


Note: Enzymes do eventually wear out, so they have to be synthesized by the cells and replaced.

-enzymes are not changed during reactions and therefore can be reused



no enzyme present

enzyme present

Intermediate :

enzyme/reactant 1

+ reactant 2

reactant 1 + reactant 2

+ enzyme


+ enzyme

Course of reaction

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new enzymes
New Enzymes
  • ** Although enzymes may be reused in cells, they eventually are destroyed and new ones must be synthesized.
  • -- begin to be destroyed above 45 C. (above this temperature all proteins begin to be destroyed)
factors influencing rate of enzyme action
Factors Influencing Rate of Enzyme Action
  • 1. pH - the optimum (best) in most living things is close to 7 (neutral) -- high or low pH levels usually slow enzyme activity
  • A few enzymes (such as gastric peptidase) work best at a pH of about 2.0
  • 2. Temperature - strongly influences enzyme activity - optimum temperature for maximum enzyme function is usually about 35-40 C. -- reactions proceed slowly below optimal temperatures -- above 45 C. most enzymes are destroyed
  • 3. Concentrations of Enzyme and Substrate
  • ** When there is a fixed amount of enzyme and an excess of substrate molecules -- the rate of reaction will increase to a point and then level off.
  • ** This leveling off occurs because all of the enzyme is used up and the excess substrate has nothing to combine with.
  • -- If more enzyme is available than substrate, a similar rx. rate increase and leveling off will occur. (The excess enzyme will eventually run out of substrate molecules to react with.)