Chapter 8: Enzymes Flashcards
Enzymes speed up metabolic
reactions by
lowering energy barriers
catalyst
is a chemical agent that speeds up a reaction without being consumed by the reaction
enzyme
is a catalytic protein
Hydrolysis of sucrose by the enzyme sucrase is an example of an
enzyme-catalyzed reaction (it’s also catabolic)
Chemical reactions involve
bond breaking & bond forming
Activation Energy (EA)
Initial energy needed to start a chemical reaction
Activation Energy (EA) is often supplied as thermal energy
that the reactant molecules absorb from their surroundings
Enzymes catalyze reactions by
lowering EA barrier
Enzymes do not affect the change in free energy (∆G); instead,
they hasten reactions that would occur eventually
∆G =
measure of capacity of a system to do work; when it’s negative, it means the reaction is spontaneous
Substrate
The reactant that an enzyme binds & acts on is called the enzyme’s
Active Site
is the region on an enzyme where the substrate binds, forming an Enzyme-Substrate Complex
Each enzyme has an optimal temperature & optimal pH in which it can function as
optimal conditions favor the most active shape for the enzyme molecule
Substrate binds to
active site of enzyme
Active site can lower an EA barrier by:
- Covalently bonding to the substrate
- Thus orienting the substrates correctly
- This strains the substrate bonds & provides a favorable microenvironment
Competitive inhibitors
bind to active site of an enzyme, competing with the substrate
Noncompetitive inhibitors
bind to another part of an enzyme, causing enzyme to change shape & making active site less effective
Enzymes are proteins encoded by genes
– Changes (mutations) in genes lead to changes in
amino acid composition of an enzyme
– Alteredaminoacidsinenzymesmayaltertheir substrate specificity
