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Ch 8 Part

Terms in this set (28)

enzyme
macromolecule that acts as a catalyst

without regulation of enzymes, chemical traffic through pathways of metabolism would be congested with chemical reactions
catalyst
chemical agent that speeds up a reaction without being consumed by the reaction
hydrolysis of sucrose
involves breaking bond between glucose and fructose

one of the bonds of a water molecule and then forming two new bonds
activation energy
free energy of activation

initial investment of energy for starting a reaction, the energy required to contort the reactant molecules so the bonds can break
law of thermodynamics favors breakdown
proteins, DNA, and other complex molecules of cell are rich in free energy-->potential to decompose spontaneously

molecules only persist because at temperatures typical for cells, few molecules can make it over the hump of activation energy
High temp is not good in biological system
high temperature denatures proteins and kills cells

heat would speed up all reactions, not just those that are needed
enzyme cataclysm
catalyzes reaction by lowering Energy activation barrier-->allows reactant molecules to absorb enough energy to reach transition state even at moderate temperatures

enzyme cannot change amount of free energy for a reaction

cannot make an endergonic reaction exergonic

can only hasten reactions that are inevitable
substrate
the reactant an enzyme acts on

enxyme binds to substrate-->forming enzyme substrate complex
enzyme substrate complex
while enzyme and substrate are joined, catalytic action of enzyme converts substrate to product of the reaction
active site
restricted region of enzyme molecule that actually binds to substrate

typically a pocket or groove on surface of enzyme where catalysis occurs

usually formed by only a few of the enzymes amino acids, rest of protein molecules providing framework for configuration of active site
induced fit
shape change makes active site fit more snuggly around substrate

like a clasping handshake

brings chemical groups of active site into positions to enhance ability to catalyze chemical reaction
enzyme shape change
due to interactions between subtrate;s chemical groups and chemical groups on the side chains of the amino acids from the active sight
most metabolic reactions are reversible
enzyme can catalyze either forward or reverse reaction

whichever has a negative change in free energy

depends on relative concentrations of reactants and products

net effect is always direction of equilibrium
substrate is held in active site by weak interactions
held by hydrogen bonds and ionic bonds
enzymes use mechanisms to lower EA and speed up reaction
active site provides template for substrates to come together in proper orientation for reaction

active site of enzyme clutches bound subtrates, enzyme may stretch from substrate molecules toward transition-state form, stressing and bending critical bonds
EA is proportional to difficulty of breaking bonds
distorting subtrate helps it approach transition state-->reduce amount of free energy that must be absorbed to achieve that state
active site and catalytic cycle of an enzyme
substrates enter active site: enzyme changes shape so active site enfolds substrated (induced fit)

substrates help by weak interations

active side can lower EA and speed up reaction by
-acting as template for substrate orientation
-stressing substrates/stabilizing transition state
-providing favorable microenvironment
-participating directly in catalytic reactions

substrates converted to products

products released

active site is available for two new substrate molecules
above certain temperature, speed pf enzymatic reaction drops sharply
thermal agitation of enzyme molecule disrupts hydrogen bonds, ionic bonds, and other weak interactions that stabilize active shape of enzyme-->protein molecule denatures
each enzyme has optimal temperature
without denaturing enzyme, temperature should allow greatest number of molecular collisions and fastest conversion of reactions to product molecules

normally about 35-50 degrees C
optimal pH
generally betweeen 6-8

most active

exceptions: pepsin, digestive enzyme in stomach, works best at ph 2
cofactors
nonprotein helpers for catalytic activity

adjuncts

may be bound tightly to enzyme as permanent residents

or may bind loosely and reversibly along with substrate

sometimes inorganic (such as zinc, iron, and copper)
coenzyme
cofactor that is organic molecule

vitamins
normal binding
substrate can bind normally to active site of enzyme
competitive inhibition
competitive inhibitor mimcis substrate, competing for active site
noncompetitive inhibition
noncompetitive inhibitor binds to enzyme away from active site, altering shape of enzyme so that even if substrate can bind, active site functions less effectively
allosteric regulation
term used to describe any case in which a protein's function at one site is affected by binding of a regulatory molecule to a separate site

may result in either inhibition of stimulation of enzyme's activity
cooperativity
substrate molecule binding to one active site in a multisubunit enzyme triggers shape change in all subunits, increasing catalytic activity of other sites

amplifies response of enzymes to substrates

one substrate molecule primes an enzyme to act on additional substrate molecules more readily

allosteric regulation because binding of the substrate to one active site affects catalysis in another active site
feedbac inhibition
metabolic pathway is switched off by the inhibitory binding of its end product to an enzyme that acts early in the pathway
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