4. Energy and Enzymes
 Definitions
 Endergonic: +∆G due to adding free energy (anabolic – make bigger e.g. amino to protein)
o Products > Reactants
o Not spontaneous
 Exergonic: - ∆G due to release in free energy (catabolic – breakdown of complex to simple)
o Reactants > Products
o Spontaneous
 Activated carrier molecule:
 Activation energy (Eₔ): The required energy to start a reaction. Leads to transition state
(bonds are broken and ready to be broken) and products.
 Active site: The region of an enzyme that recognizes binds to the substrate
o Substrate: Molecule that enzyme catalyzes
o Catalysis: Introduction of a catalyst (e.g. enzyme) into a reaction
 Cofactors: atoms/molecules other than proteins. Some enzymes require this to function.
May be inorganic metal ions (e.g., iron, copper, zinc), or organic cofactors/coenzymes (e.g.,
NAD+, NADP+, vitamin C). e.g., catalase – enzyme that detoxifies free radicals; requires iron
cofactor.
 Inhibitors – prevent substrate from binding to enzyme
o Competitive: Inhibitor molecule closely resembling substrate, binds to active site to
prevent bonding of substrate
o Noncompetitive: Binds to enzyme to alter the shape, preventing bonding of
substrate. Enzyme becomes inactive (e.g. poisons)
 Allosteric inhibition – Molecule binds to allosteric site, leading to
stabilization of inactive enzyme
 Feedback inhibition – Product of a reaction acts as a regulator
 Metabolism
 The sum of the chemical reactions on the body
 Energy released by catabolic reactions is used to power anabolic reactions
o E.g. ATP => ADP + Pi (catabolic) => ATP (anabolic)
 ATP
 3 phosphate groups, 1 5-C sugar (ribose) molecule, nucleotide base (adenine)
 Hydrolysis
 Reactants: ATP and H2O
 Products: ADP and inorganic phosphate molecule (Pi)
 ∆G = -7.3 kcal/mol
 Enzymes
 Act as catalysts for biological reactions
 Decrease Activation Energy
 Bring substrates closer together
 Conformational changes and Act as ideal environment