AP Biology Chapter 8: An Introduction to Metabolism (8.4: Enzymes speed…
AP Biology Chapter 8: An Introduction to Metabolism
An organism's metabolism transforms matter an energy, subject to the
Laws of Thermodynamics
Free energy, stability, and equilibrium
Totality of an organism's
chemical reactions =
= a sequence of chemical reactions undergone by a compound in a living organism, start with substrate end with product
Anabolic pathway = simple to complex (build up); catabolic pathway = complex to simple (break down)
= energy of position (ex: diver up on dive board)
= every of motion (ex: diver actually diving)
= energy within bonds of a chemical reaction (ex: starting up cars.)
= kinetic energy associated with random movements of atoms/molecules.
is the free energy equation.
Delta G = free energy; delta H = change in enthalpy (total energy); T= temperature (in K); (delta)S=change in entropy (randomness of assortment)
Exergonic = energy not needed in reactants; spontaneous; products have less free energy than reactants; negative G
Endergonic= energy is needed in reactants; non spontaneous; positive G
1st Law of Thermodynamics
= energy is transferrable & transformable, but NOT created or destroyed.
2nd Law of Thermodynamics
= Every energy transfer/transformation increases the entropy of the universe.
ATP powers cellular work by coupling exergonic reactions --> endergonic reactions
3 types of cell work:
(ex: synthesizing polypeptides from monomers,
(ex: membrane diffusion),
(ex: contraction of muscle cells.)
ATP is used in coupled reactions as an immediate energy source to push endergonic reaction
Hydrolysis of ATP yields ADP + P1 which releases free energy
Enzymes speed up metabolic reactions by lowering energy barriers
Activation energy barrier
=energy needed to speed up a chemical reaction;
activation energy (Ea)
= energy needed to start a chemical reaction.
Key concept: although exergonic reactions require no energy to begin, they're
slow. Enzymes help speed up the reactions by lowering the time it takes reactions to reach the
, or the point of the chemical reaction in which the Ea is activated
Enzymes speed up reactions in 1/4 ways:
as a template for substrate orientation
substrates and stabilizing transition state
directly in catalytic reaction.
Temperature and PH are usually the factors that determine enzyme activity, as well as:
Competitive enzyme inhibitors
= binds directly to active site, blocking substrates from binding.
= binds to other place on enzyme to change its shape and not allow substrate to bind
= nonprotein enzyme helpers.
= organic cofactors.
Regulation of enzyme activity helps control metabolism
= term used when a protein's function at one site is affected by the binding of a regulatory molecule to another site.
3 types of allosteric regulation:
activators, inhibitors, and cooperativity
bind to an active site of an enzyme to stabilize (or "lock") the enzyme in it's active form.
do just the opposite: they bind to lock an enzyme in it's inactive form.
is another form of allosteric activation. Instead of an activator binding to an enzyme's active site though, it's a substrate
at low concentrations, inhibitors and activators dissociate from enzyme, allowing it to again bind to its substrate.
Inactive form in cooperativity oscillates with active form when the active form is not stabilized by a substrate.
= when the product of a metabolic pathway allosterically binds to an enzyme and inhibits it.