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bich test 3

QuestionAnswer
oxidoreductase catalyze oxidation/reduction reactions NAD/NADH
transferase catalyze group transfer
hydrolase catalize hydrolysis reactions look for water!
lyase catalize lysis of substrate generate a double bond often called "synthases"
isomerase structural change within a SINGLE monecule
ligase catalize a joining of two molectules (ligation) require energy input often called "synthETases"
cofactor a small metal ion that is associated with an enzyme that facilitates the reaction
coenzyme a small organic molecule that is associated with an enzyme that facilitates the reaction
cosubstrate a coenzyme or cofactor that only has transient/loose association with the enzyme another enzyme regenerates the coenzyme/cofactor
Prosthetic group coenzyme that has Permanent association with the enzyme a separate phase of the same enzymatic reaction sequence allows for the coenzyme/cofactor to regenerate
Arrhenius equation e^(-dG**/RT)
rate enhancement equation e^(ddG**/RT) Kcatalyzed/Kuncatalyzed
three assumptions for MM equation 1. don't have a high [] of enzyme in bio. systems, so [S]t=[S]free 2. ignore the backwards-catalyzed rxn 3. upon mixing E+S, [ES] reaches a STEADY STATE EQ. Vmax=K2[ES]
MM equation Vo=(Vmax[S]t)/(Km+[S]t)
catalytic constant (turnover number) Kcat=Vmax/[E]t
catalytic efficiency =-Kcat/Km
reversible inhibitor a substance that binds to an enzyme to inhibit it, but can be released non-covalent bonds Dead End or Product
Dead End reversible inhibitor a compound that is NOT part of the rxn, but looks like either a substrate or a product
Product reversible inhibitor the product of a reaction inhibits the enzyme that catalyzes the enzyme is part of a normal reaction
irreversible inhibitor a substance the causes inhibition that cannot be reversed covalent bonds preferred in drugs over reversible inhibitor
competitive inhobitor competes with the substrate for the enzyme-substrate binding site double reciprocal plot: lines cross on y-axis R=Km(I)/Km(noI)=slope(I)/slope(noI)
uncompetitive inhibitor binds to enzyme substrate complex parallel lines on double reciprocal plot R=yint(I)/yint(noI)=xint(I)/xint(noI)
mixed inhibitor bind to E and ES in unequal amounts if KiKi' lines cross in 3rd R=yint(I)/yint(noI)=slope(I)/slope(noI)
pure non-competitive binds to E and ES in equal amounts (Ki=Ki') lines cross on x axis on double reciprocal plot R=yint(I)/yint(noI)=slope(I)/slope(noI)
Equilibrium constant of inhibitor (Ki) Ki=[I]/(R-1)
sequential raction all substrates must bind to the enzyme before the reaction occurs and products are released will have intersecting lines on Vo double reciprocal plot
ordered sequantial rxn substrates bind in a specific order and products come off in a specific order (A on, B on, rxn, P off, Q off)
random sequantial rxn all products come on before rxn occurs, but in any order (A or B on, A or B on, rxn, P or Q off, P or Q off)
ping-pong rxn one or more products are released before all substrates have been added; alternate stable enzyme form (F) is produced in the half reaction will have parallel lines on Vo double reciprocal plot
proximity and orientation effect substrates are oriented in the optimum way for chemistry to occur reduces entropy
transition state optimization complimentarity to substrate less helpful than complimentarity to transition state; need a space for rxn. to occur
three basic types of enzyme mechanisms acid-base catalysis covalent catalysis metal ion catalysis
types of acid-base catalysis general acid catalysis general base catalysis concerted acid-base catalysis
general acid catalysis general acid DONATES a PROTON to substrate enzyme active site must be protonated
general base catalysis general base ACCEPTS a PROTON from the substrate enzyme active site must be deprotonated
concerted acid-base catalysis a general acid and a general base (on enzyme) both participate in the reaction with the substrate
covalent catalysis covalent bond is transiently formed between the substrate and the enzyme (or coenzyme) usually a NUCLEOPHILIC group on ENZYME and [electrophilic] group on [substrate]
metalloenzymes enzymes that contain tightly bound metal cofactors
metal activated enzymes enzymes that are only loosely bound to metal ions
Serine protease examples -thrombin (blood clotting) -(chymo)trypsin, elastase (digestive enzyme) -subtilisin (bacterial protease) -plasmin (anti-clot) -tissue plasminogen activator (TPA, makes plasmin, stroke indicator)
the catalytic triad the active sites of trypsin, chymotrypsin, and elastase are all composed of His, Asp, and Ser
zymogens (proenzymes) inactive precursors that are irreversibly activated by specific proteolytic cleavage
isozymes enzymes with similar but not identical aa sequence and catalyze the SAME rxn different Km and Vmax values use different effectors/forms of enzyme e.g. lactate dehydrogenase (A4 is glucokinase, liver; is hexokinase in muscles)
allosteric regulation used for multi-subunit proteins, do NOT obey M-M kinetics (sigmoidal instead of hyperbolic)
covalent modification enzymes are used to convert the regulatory enzyme to an active A form or inactive B form; reversible, covalent changes are made to specific aa side chains
Created by: Jessica S Jessica S on 2012-11-16



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