BIOCHEMISTRY
PRELIMINARY SY. 2023-2024
Lecture/First Semester/Week 4
ENZYMES
What are enzymes?
- Catalysts
- substances that speed up chemical reactions
- enzymes are specific for one particular reaction or
group of related reactions
- many reactions cannot occur without the correct
enzyme present
General Characteristics of Enzymes
Enzymes are well-suited to their roles in three major ways:
- they have enormous catalytic power
- they are highly specific
- their activity can be regulated
Enzymes Parts
- Apoenzyme
- enzymatically inactive protein part of an
enzyme, which requires a cofactor for its
activity
- Cofactor
- a non-protein chemical compound or metallic
ion that is required for an enzyme's role as a
catalyst
- Proenzyme or zymogen
- a biologically inactive substance which is
metabolized into an enzyme.
- Coenzyme
- organic compounds required by many
enzymes for catalytic activity
Enzymes Nomenclature
- Trivial System
- based on the substrate of the enzyme and the
type of reaction catalyzed
- use of -ase ending
- International Enzyme Commission
- groups enzymes into six classes
Main Classes of Enzymes
Properties of Enzymes
- enzymes are proteins
- enzymes are catalysts
- enzymes are highly specific
Chemical Reactions
- All chemical reactions require an initial input of energy
called activation energy
- reactions become more likely to happen if their
activation energy is lowered
- this process is called catalysis
- catalyzed reactions proceed must faster than
non-catalyzed reactions
Main Classes of Enzymes
How Enzymes Work
- enzymes bind specifically to a molecule and stress the
bonds to make the reaction more likely to proceed
- active site is the site on the enzyme that binds to a
reactant
- binding site is the site on the reactant where the
enzyme binds
- the binding of the reactant to an enzyme causes the
enzyme's shape to change slightly - leading to an
"induced fit"
- the enzyme lowers the activation energy for the
reaction
- the enzyme is unaffected by the chemical reaction and
can be reused
Mechanism of Enzyme Action
- Lock and Key Theory
- enzymes have a specific shape that directly
correlates to the shape of the substrate.
- Induced Fit Theory
- an enzyme's shape and conformation
changing over time in response to substrate
binding.
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