6 2 enzymes and chemical reactions pages 156 160
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6.2 Enzymes and Chemical Reactions pages 156-160. Chemical reactions take place all the time. Chemical reactions change substances into different ones by breaking and forming chemical bonds . Reactants are the starting materials.

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Chemical reactions take place all the time.

  • Chemical reactions change substances into different ones by breaking and forming chemical bonds.

Reactants are the starting materials.

  • The newly formed substances are called products, which are different from the reactants.
  • Reactants on the left, Products on right.

For example:

6CO2 +6H2O+light energyC6H12O6 + 6O2




The key to starting a chemical reaction is energy.

  • Activation energy is the minimum amount of energy needed for reactants to form products in a chemical reaction.
enzymes in chemical reactions
Enzymes in Chemical Reactions
  • Sometimes, the energy required for a reaction to take place is too high.
  • The reaction can’t take place unless additional substances are present to reduce the activation energy.
  • These additional substances are known as catalysts.
  • Enzymes are catalysts.

A catalyst lowers activation energy

  • Catalysts are substances that speed up chemical reactions
    • by decreasingactivation energy.

Enzymes are catalysts in


Most reactions would occur too slowly without the help of enzymes, which speed up chemical reactions.


Characteristics of Enzymes

  • Enzymes are proteins
  • 2. Enzymes are reusable!
  • 3. Enzymes denature in high temperatures
    • * denature = destroyed, broken apart, digested
    • * denaturation is not reversible
  • All enzymes end with ‘ase’.
  • Ex) Lactase breaks down Lactose (milk sugar)

Substrates bind to anenzyme at certain places called active sites.

The enzyme bringssubstrates together and weakens their bonds.

The catalyzed reaction formsa product that is releasedfrom the enzyme.

The lock-and-key model helps illustrate how enzymes function.

  • Enzymes are SPECIFIC (they only break down/put together one specific substance.)
    • *They will only FIT with certain substrates*
  • Substrates are brought together.
  • They attach to the active site of enzymes.
  • - Bonds are then made or broken.
  • - Product is released.
induced fit model
Induced Fit Model
  • Builds on the “Lock and Key” Model.
  • It adds that the enzyme active site physically changes to mold around and encompass the substrate(s).

An Enzyme at Work






Active site



how do enzymes speed up reactions
How do enzymes speed up reactions?
  • Enzymes lower the activation energy of a reaction:
factors that affect enzyme activity
Factors that Affect Enzyme Activity
      • Too warm, enzyme will denature.
      • Too cold, enzymatic activity will slow down.

2. pH

- a change in pH can change the shape of the enzyme so that substrates can’t fit into active site.


1. What is this graph showing?

temperature and enzyme activity

2. What is the independent variable?


3. What is the optimum temperature for the enzyme?


4. At what temperature is the enzyme completely denatured?


  • Enzymes – biological catalysts or special proteins that speed up chemical reactions
  • Catalysts – substances that speed up chemical reactions)
  • Substrates – materials that bind to the enzyme
  • Active Site - Location on the enzyme where the substrate binds

If you did not complete lab. Do that FIRST!

  • Enzyme worksheet
  • Pg 160 1 and 4
  • Pg 175-176: 1,2,4,7,14-23