Enzymes Flashcards
Enzyme
A macromolecule that acts as a catalyst: A chemical agent that speeds up a reaction without being consumed by the reaction
–> Organic biological catalyst
–> Ends in -ase
Substrate
The molecule (reactant) on which the enzyme acts upon
Bond Breaking vs Forming
Bond Breaking = Input Energy
Bond Forming = Release Energy
Endergonic
Absorbs more energy than is released
Exergonic
Releases more energy than is absorbed
Activation Energy
(Ea) Energy required to initially break bonds (start the reaction) –> Get over the hump
Delta G
Net free energy released
Energy of Products - Energy of Reactants
Enzymes and Activation Energy
Enzymes lower activation energy for reactions, they DO NOT lower Delta G
Catalytic Cycle of an Enzyme
1) Enzyme and substrate are available
2) Substrate binds to enzyme –> (Forms “enzyme-substrate” complex)
3) Substrate is converted to products and products are released
Active Site
The specific region of an enzyme that binds the substrate and that forms the pocket in which catalysis takes place
Properties of Enzymes (4)
1) Enzymes lower activation energy
2) Enzymes are usually proteins
3) Enzymes are usually named by adding (-ase) to the end of substrate name
4) Enzymes are substrate specific
–> However, not lock and key model, follows induced fit model
How Enzymes Work: 3 possibilities
1) In reactions with 2 or more reactants: Active site provides template on which substrates can come together with proper orientation to react
2) Stretch and Strain Bonds: Active site clutches bound substrate and stretches them towards their transition state form (Lowers Ea)
3) Create Favorable Microenvironment (Ex: providing more acidic environment)
Vmax
Maximum reaction rate –> All enzymes “full and working”
Enzyme Saturation
All enzymes at full capacity:
Only way to increase reaction rate in this case is to increase number of enzymes
Km
Concentration of substrate at which enzyme works at 1/2 the max rate
–> Indicates how tightly the substrate is bound to the enzyme
1) Greater Km = Lower Binding Affinity
2) Lower Km = Higher Binding Affinity
Effects of Environmental Conditions
Changes to temp, pH, or salinity can alter enzymatic function
Cofactors
INORGANIC –> Usually divalent cations (minerals—EX: Mg2+, Ca2+, Mn2+)
Any non-protein molecule or ion that is required for the proper functioning of an enzyme
Coenzymes
ORGANIC –> Mostly vitamins
Supply reactive atoms that are necessary for the reaction but are not available at the active site
Competitive Inhibitor
A molecule that directly competes with the substrate for the active site
BINDS TO THE CATALYTIC SITE
–> A physical block: Can be removed by adding more SUBSTRATE
Non-Competitive Inhibitor
A molecule that binds outside the active site (NO PHYSICAL competition)
–> Inhibits by causing changes to the conformation of the active site (so that the substrate can’t bind)
Allosteric Regulation
A reversible, non-competitive inhibitor (like a light switch)
–>Must have 2 sites: Active and allosteric
Allosteric Regulators
Regulators bind to the allosteric site to change activity of enzyme
1) Activator = Stabilizes the active conformation of the active site
2) Inhibitor = Stabilizes the INactive conformation of the active site
Cooperativity
A form of allosteric activation
–> The binding of one substrate molecule facilitates the binding of other substrate molecules
(Has multiple active sites)
Feedback Regulation
The final product of a chain of enzymatic reactions allosterically inhibits the first enzyme of the chain
–> Essentially turns itself (the chain reaction) off
–> Prevents the uncontrollable accumulation of products
