Introduction to Enzyme

Enzymes

Lecture outlines
•Catalysis
profile

•Activation energy & its
•Enzyme & substrate

substrates

•How enzymes bind to
•Lock & Key model
•Induced-fit model
•Enzyme assay

Lecture outcomes
• At the end of this lecture, students are able to:
• Define the catalyst
• Understand how enzymes work as catalysts, the concept of activation energy and enzymes-substrate binding
• Explain different theories of the relation between enzymes and substrates

Catalysis
• It is probably the most important function of all proteins • Most reactions in biological systems would take place far too slowly in the absence of catalyst
• The catalysts that serve this organisms are called enzymes

function

in

• All other enzymes are globular proteins (with the exception of some RNAs (ribozymes) that have catalytic activity)

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• Enzymes can increase the rate of a reaction by factor of up to 1020 over uncatalyzed reactions
• Non-enzymatic catalysts typically enhance the rate of the reaction by factors of 102 to 104
• Catalysts are substances that speed up the rate of a chemical reaction
• Biocatalysts or enzymes are biological catalysts that speed up the metabolic reactions that occur in the body

Catalase

2 H2O2 ⇄ H2 O + O2

3% of hydrogen peroxide in water at 37ºC
a = no catalyst added
b = with Fe3+ salt
c = with enzyme (catalase)

Hydrogen peroxide
• Hydrogen peroxide is a waste product of metabolism, and if it left in the cell, it would initiate the formation of free radical

Activation energy
• The amount of energy that must be acquired by reactant molecules before they can be converted to a product
• It shows the intermediate stages of a reaction, those between the initial and final states.
• It directly affects the rate of reactions.
• It speeds up a reaction by changing the mechanism and thus lowering the activation energy Continue

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Plots

the

energies