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AP Biology Chapter 8: An Introduction to Metabolism (8.4: Enzymes speed up…
AP Biology Chapter 8: An Introduction to Metabolism
8.1:
An organism's metabolism transforms matter an energy, subject to the
Laws of Thermodynamics
;
8.2:
Free energy, stability, and equilibrium
Totality of an organism's
chemical reactions =
metabolism
metabolic pathway
= 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)
Potential energy
= energy of position (ex: diver up on dive board)
kinetic energy
= every of motion (ex: diver actually diving)
chemical energy
= energy within bonds of a chemical reaction (ex: starting up cars.)
Heat
= kinetic energy associated with random movements of atoms/molecules.
8.2
[(delta)G=(delta)H-T(delta)S]
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)
8.2
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.
8.3:
ATP powers cellular work by coupling exergonic reactions --> endergonic reactions
3 types of cell work:
chemical
(ex: synthesizing polypeptides from monomers,
transport
(ex: membrane diffusion),
mechanical
(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
8.4:
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
super
slow. Enzymes help speed up the reactions by lowering the time it takes reactions to reach the
transition state
, or the point of the chemical reaction in which the Ea is activated
Enzymes speed up reactions in 1/4 ways:
-
acting
as a template for substrate orientation
-
stressing
substrates and stabilizing transition state
-
providing
favorable environment
-
participating
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.
Non-competitive inhibitors
= binds to other place on enzyme to change its shape and not allow substrate to bind
Cofactors
= nonprotein enzyme helpers.
Coenzymes
= organic cofactors.
*8.5:
Regulation of enzyme activity helps control metabolism
Allosteric regulation
= 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
activators
bind to an active site of an enzyme to stabilize (or "lock") the enzyme in it's active form.
Inhibitors
do just the opposite: they bind to lock an enzyme in it's inactive form.
cooperativity
is another form of allosteric activation. Instead of an activator binding to an enzyme's active site though, it's a substrate
Note:
at low concentrations, inhibitors and activators dissociate from enzyme, allowing it to again bind to its substrate.
Note:
Inactive form in cooperativity oscillates with active form when the active form is not stabilized by a substrate.
Feedback inhibition
= when the product of a metabolic pathway allosterically binds to an enzyme and inhibits it.