Page 38 - Clinical biochemistry

• All chemical reaction in living cell have an energy barrier separating reactants

(substrates) from products (Free energy of reaction).

• Substrates must be energized (absorb energy) to reach activated form (transition

state).

• Amount of energy required to raise all molecules in one mole of substrate to

transition state is called activation energy.

• Enzymes decrease activation energy thus accelerate reaction rate
• Enzymes prevent uncontrolled or spontaneous reactions and allow reactions to

occur at a rate appropriate to the cell needs

• What is the difference between an enzyme reaction and its mechanism?
• An enzyme reaction is the chemical transformation from reactants to products,

which is catalysed by an enzyme. The E.C. classification describes the overall
transformation performed by the enzyme.

• The enzyme mechanism, however, can consist of several steps, and sometimes

the same enzyme (as defined by its E.C. number) can have different
mechanisms to achieve the same overall transformation.

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