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Enzymes. ENZYMES. An enzyme is a catalyst protein that changes the rate of a chemical reaction by lowering the amount of energy needed for reaction. Reaction involves: Enzyme - speed up reaction Active site – pockets specific to substrates

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Presentation Transcript
  • An enzyme is a catalyst protein that changes the rate of a chemical reaction by lowering the amount of energy needed for reaction.
  • Reaction involves:
    • Enzyme - speed up reaction
    • Active site– pockets specific to substrates
    • Substrate– substance which the enzymes acts upon
Catalyst- a chemical that changes the rate of a reaction without being used up in the reaction.

Energy needed without the enzyme.

Energy needed with the enzyme.

Enzyme speed reactions by lowering the activation energy.

It speeds reactions that would occur eventually anyway.

A substrate is a reactant that binds to an enzyme.

When a substrate binds to an enzyme, the enzyme catalyzes the conversion of the substrate to the product.


Enzymes Characteristics

Enzymes have an active site

2. Each enzyme works for a specific substrate

3. The enzyme is unaffected by the reaction;

it is recycled.

The active siteof an enzymes is typically a pocket or groove on the surface of the protein into which the substrate fits.

This is an example of how the substrate binds to the active site.

The specificity of an enzyme is due to the fit between the active site and that of the substrate.

Compare it to a “lock and key”

As the substrate binds, the enzyme changes shape leading to a tighter induced fit, bringing chemical groups in position to catalyze the reaction.

Enzyme Active Site



Enzyme – Substrate Complex

A single enzyme molecule can catalyze thousands or more reactions a second.

Enzymes are unaffected by the reaction and are recycled.

enzymes a fun introduction
Enzymes – A Fun Introduction
  • https://www.youtube.com/watch?v=XTUm-75-PL4 (5 MIN)
why are enzymes important
Why are enzymes important?

Help maintain homeostasis by speeding up metabolic chemical reactions.

Enzymes catalyze the thousands of reactions that need to take place in order to maintain life.


  • digestion
  • respiration
  • photosynthesis (plants and some bacteria)
enzymes names
Most enzymes are named for the reaction they help

sucrase breaks down sucrose

Pepsin breakdown proteins

lipasesbreakdown lipids

DNA polymerasebuilds DNA

Amylase breaks down starch

Catalase breaks down hydrogen peroxide

Enzymes Names

Oh, I get it!

They end in -ase

factors affecting enzymes
Factors affecting enzymes

The rate of enzyme–catalyzed reactions depends on several factors.

Factors that affect the rate of a reaction include:

  • temperature
  • substrate concentration
  • pH
  • surface area
  • enzyme concentration
  • pressure.

All enzymes work best at only one particular temperature and pH: this is called the optimum.

Different enzymes have different optimum temperatures and pH values.