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BIOCHEM Lecture 03
exam 1
Question | Answer |
---|---|
thermodynamics | determines if a reaction will happen |
kinetics | determines how fast a reaction will happen |
free energy change | energy available to do work, G products - G reactants |
if delta G is positive | endergonic, nonspontaneous, products have more free energy |
if delta G is negative | exergonic, spontaneous, reactants have more free energy |
if delta G equals 0 | equilibrium, same free energy in products and reactants |
standard free energy change | temperature, pressure, concentration, pH, useful for comparisons |
delta G equation | standard delta G + RT ln [C][D]/[A][B] |
how do cells allow positve delta standard delta G to occur | alters concentrations of reactants and products |
enzymes | catalysts that speed chemical reactions, made up of proteins |
enzyme specificity | not permanently altered and highly specific for substrates |
how do enzymes affect activation energy? | enzymes lower the activation energy to speed up the reaction |
active site | portion of enzyme that the substrate binds |
apoenzyme | inactive enzyme that requires cofactor for activation |
cofactor | non protein molecule necessary to activate apoenzyme |
what can be cofactors? | metals or coenzymes |
holoenzyme | active enzyme made up of apoenzyme and cofactor |
energy substrate interactions must be ___________ | sterically possible and energetically favorable |
acid base catalysis | enzyme active sites donate or accept hydrogen ions from substrate |
covalent catalysis | enzyme active site creates a temporary covalent bond with the substrate |
metal ion catalysis | metal can stabilize ionic intermediates (transition state) |
orientation catalysis | enzymes hold multiple substrates in the optimal position |
oxidoreductase | transfer of electrons |
transferase | transfer of functional groups |
hydrolase | hydrolysis, cutting with water |
lyase | removal of groups without hydrolysis |
isomerase | rearrangement to make isomers |
ligase | joining of two molecules |
general kinetics | d[product]/dt |
collision theory | more concentrated reactions have a faster reaction |
zero order | rate is not affected by concentration of reactant |
first order | only one reactant, doubling the concentration will double the rate |
pseudo first order | two reactants present but only one affects the rate |
second order reaction | two molecules of reactant |
Michaleis-Menten model | [S] is similar to [E] |
M-M enzymes | catalyst but not regulatory |
michaelis constant Km | [S] at one half of V max |
Vmax | max turnover of substrate when enzyme is saturated |
lower Km | higher binding affinity |
Kcat | number of substrate molecules converted to product per unit time |
high Kcat | more efficient enzyme |
Lineweaver-Burk Plot | y intercept = 1/Vmax |
x intercept = -1/Km | |
allosteric enzymes | catalysts and regulator of metabolic pathways |
allosteric enzyme: allosteric site | effector binding (inhibitor and activation) |
allosteric enzyme: active site | substrate binding |
allosteric cooperativity | substrate binding changes affinity of other subunits |
single headed arrow | irreversible, committed step |
double headed arrow | reversible, not committed |
allosteric enzyme catalysis | catalyze first committed step |
negative feedback | accumulation of end product inhibits enzyme that catalyzes first committed step |
positive feedback | accumulation of end product catalyzes enzyme for first committed step |
allosteric enzyme repression | repressor binds to enzyme, changes active site conformation so that substrate cannot bind |
allosteric enzyme activation | activator binds to enzyme and corrects active site conformation so that the substrate can bind |
activators stabilize the ___ form | active |
inhibitors stabilize ___ form | inactive |
competitive inhibitors | compete with substrate for active site, can be overcome with high substrate |
noncompetitive inhibitors | bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective, cannot be overcome with high substrate |
uncompetitive inhibitors | bind to ES complexes and prevent product release, cannot be overcome with high substrate |
Same Vmax, different Km | competitive inhibitor |
Different Vmax, same Km | noncompetitive inhibitor |
different Vmax, different Km | uncompetitive inhibitor |
How do temperature and pH affect enzymes? | each enzyme has an optimum temperature and pH that allow it to be most active |