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49 Cards in this Set
- Front
- Back
What is an enzyme?
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A protein catalyst that increases the rate of reactions w/o being changed in the overall process
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What is a synthetase?
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Requires ATP to function
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What is a synthase?
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no ATP required to function
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What is a phosphatase?
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Uses water to remove a phosphoryl group
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What is a phosphorylase?
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Uses Pi to break a bond and generate a phosphorylated product
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What is a dehydrogenase?
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NAD/FAD is electron acceptor in redox reactions
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What is a oxidase?
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O2 acceptor but oxygen atoms are not incorporated into substrate
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What is a oxygenase?
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One or both oxygen atoms are incorporated
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What are RNAs w/ catalytic activity?
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Ribozymes
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What does the active site contain?
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Amino acid side chains that participate in substrate binding and catalysis
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What is the induced fit model?
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The enzyme undergoes a conformational change that allows catalysis of the enzyme
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What is the holoenzyme?
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The active enzyme w/ its nonprotein component
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What is a apoenzyme?
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The enzyme w/o its nonprotein moiety, the inactive form
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What is a cofactor?
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If the nonprotein moiety of an enzyme is a metal ion such as Fe3+ or Zn2+
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What is a coenzyme?
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IF the nonprotein moiety of an enzyme is small organic molecule
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What are cosubstrates?
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Coenzymes that only transiently associate w/ the enzyme
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What are coenzymes frequently derived from?
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Vitamins
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What is the purpose of enzyme compartmentalization?
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Serves to isolate the reaction substrate or product from other competing reactions
Also provides a favorable environment for the reaction, and organizes the thousands of enzymes present in the cell into purposeful pathways |
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What is the free energy of activation?
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The energy difference b/e that of the reactants and a high-energy intermediate that occurs during the formation of product
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What do molecules need in order to react?
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Enough energy to overcome the energy barrier of the transition state
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What is accomplished by the enzyme stabilizing the transition state?
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Greatly increases the concentration of the reactive intermediate that can be converted to product and accelerates the reaction
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What is the enzymes maximal velocity?
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The rate of a reaction is the number of substrate molecules converted to product per unit time
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What enzymes do not follow michaelis-menten kinetics?
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Allosteric enzymes
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What effect on reaction velocity does temperature have?
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Increased temperature increases the rate of the reaction by adding more energy
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What happens to reaction velocity if you heat it too hot?
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The enzymes denature and reaction velocity decreases
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What is the michaelis-menton equation?
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v0 = (Vmax[S])/(Km + [S])
v0 = initial reaction velocity vmax = maximum reaction velocity [S] = substrate concentration Km = constant |
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What assumptions are made by the michaelis-menton equation?
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1. [S] >>> [E]
2. [ES] does not change w/ time 3. The rate of the reaction is measured as soon as enzyme and substrate are mixed |
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What is Km equal to?
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Numerically equal to the substrate concentration at which the reaction velocity is equal to 1/2Vmax
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What does Km reflect about the enzyme? what does a low Km mean? high Km?
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The affinity of the enzyme for that substrate
low Km = high affinity of enzyme for substrate high Km = a low affinity of enzyme for substrate |
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What is the relationship of velocity to enzyme concentration?
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The rate of the reaction is directly proportional to the enzyme concentration at all substrate concentrations
*i.e. when [E] is halved, v0 is halved too |
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What is the order of a reaction?
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first order: When [S] is much less than Km, the velocity of the reaction is approximately proportional to the substrate concentration
zero order: When [S] is much greater than Km, the velocity is constant and equal to Vmax, and rate is independent of [S] |
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What is competitive inhibition?
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When the inhibitor binds reversibly to the same site that the substrate would normally occupy
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What is competitive inhibition's effect on Vmax? Km? lineweaver-burk plot?
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Vmax = effect of competitive inhibitor is reversed by increasing [S], so reactions eventually reach the Vmax
Km = increases the apparent Km, so more substrate is required to reach 1/2Km L-B = shows a characteristic plot where the inhibited and uninhibited plots intersect on the y-axis at 1/Vmax |
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What is noncompetitive inhibition? what is its effect on Vmax? Km? L-B?
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When inhibition occurs at a site other than the active site
Vmax = decrease the apparent Vmax of a reaction Km = does not interfere w/ binding, so same Km L-B = Apparent Vmax decreases |
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What is the function of allosteric enzymes?
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Alter the affinity of the enzyme for its substrate, or modify the maximal catalytic activity of the enzyme or both
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What role does alanine play in the liver?
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Transfers ammonia equivalents to the liver for processing into urea
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What is the function of the ALT enzyme? What does it require to function?
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Plays a critical role in amino acid catabolism
The vitamin B6 derivative PLP ("pyridoxal-5'-phosphate") |
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What cofactor do many neurotransmitters require for their synthesis?
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PLP
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Which Michaelis-Menten kinetic parameters correlate with enzyme concentration?
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v0
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Which Michaelis-Menten parameter depends on substrate concentration? why?
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Vmax;
b/c the Vmax is determined by how much substrate you can add before you reach maximum reaction speed |
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Which Michaelis-Menten kinetic parameter indicates relative substrate preferences? why?
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Kcat/Km
b/c Kcat/Km is the specificity constant and represents the enzymes ability to catalyze a particular substrate, so the lower Km and the higher Kcat the better the substrate binds to the enzyme |
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What are the kinetics of indicator reactions characterized by?
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low Km values and high activity
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What is the effect of pH on enzymes?
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There is a very narrow pH range where enzymes function w/o denaturing, so the pH must be strongly buffered
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What would you consider a compound that binds to an enzyme w/o being modified?
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A potential inhibitor
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Where do Competitive, noncompetitive and mixed inhibitors intersect on a lineweaver-burk plot?
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Competitive inhibitors intersect on the y-axis
noncompetitive inhibitors intersect on the x-axis mixed inhibitors intersect somewhere in outerspace and not on a axis |
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What effect do mixed inhibitors have on binding to the enzyme-substrate complex?
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Mixed inhibitors change the conformation of the active site and prevent substrate binding. SO it has the characteristics of competitive inhibition, but does not bind to the active site
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What effect will binding of a substrate to part of an allosteric effector have?
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Will change the conformation of all sites
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What is the most common enzyme that is inhibited by uncompetitive inhibition?
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bisubstrate enzymes
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What effect on apparent Km do competitive inhibitors have?
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Make the apparent Km larger
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