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How Does Enzymes Work?

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Enzymes are highly specific, acting upon a single substrate or group of related substrates.  Enzymes have an active site - a small portion of the molecule which is complementary in shape to a portion  of the substrate. The substrate binds to the active site of the enzyme  forming the enzyme-substrate complex. Strain is induced in the bonds causes them to cleave and the the products leave the active site, leaving it available for further reactions. The reaction of enzymes are reversible.
How Enzymes Work Animation ( You Tube Video )

Enzyme Inhibitors & Co-Factors

Enzymes may be inhibited by inhibitors - molecules which reduce the rate of an enzyme-catalyzed reaction. Inhibitors may be other biological molecules, playing a role in regulation of cell activity.  Other inhibitors may be foreign -such as  drugs or poisons - and may have a therapeutic or deleterious effect. Inhibitors may be competitive or non-competitive, reversible or irreversible.
Some enzymes require co-factors - non-protein components which bind to the enzyme and modify its active site to its ideal configuration for formation of the enzyme-substrate complex.  Co-factors may simply increase the activity of the enzyme or may be necessary for its action.

There are 3 types of co-factors
  • inorganic ions e.g.  the presence chloride ion increases activity of salivary amylase
  • prosthetic groups (organic molecules which includes vitamins)  e.g.  Haem and Flavine Adenine Dinucleotide (FAD) containing riboflavin ( vitamine B2)
  • coenzymes  e.g.  Nicotinamide Adenine Dinucleotide (NAD), Nicotinamide Adenine Dinucleotide Phosphate (NADP), coenzyme A and Adenosine Tri-phosphate (ATP)


Learning Objectives

  • Explain the properties and functions  of enzymes
  • Explain how various factors  - pH, temperature, substrate concentration, enzyme concentration - can affect the rate of enzyme-catalyzed activity
  • Explain the action of inhibitors - competitive or non-competitive, reversible or irreversible.

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