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67 Cards in this Set
- Front
- Back
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What two parameters does every reaction have?
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direction and speed
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What affects direction?
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Not catalyst.
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What affects Rate?
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Presence of a catalyst.
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What is the Gibbs-Helmholtz equation
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(delta)G=(delta)H-T(delta)S
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What is enthalpy?
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The heat content of the molectule and total chemical potential energy of the molecules (incl.bond energies)
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What does it mean if delta H is positive?
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Energy is gained by the system -> product contains more bond energy than reactants.
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What is S?
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Entropy, degree of randomness/chaos of the system; energy unavailable for work.
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What does it mean if delta S is positive?
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The products are more disordered than the reactants.
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What three forms can S take in molecules?
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1) degree of rigidity of the molecules 2) Degree of orderly arrangement of the molecules [e.g. gas vs. liquid] 3) Number of molecules/ions [more molecules = greater entropy]
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How does S relate to the energy level of the system?
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Increasing S lowers the energy level of the system and vise versa.
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What is G?
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The free energy available to do work.
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What units are delta G expressed in?
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calories or joules per mole.
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What kind of reaction is energetically favorable?
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negative delta G
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What does it mean if delta g is zero?
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The reaction is at equilibrium -> no change in concentrations of products and reactant.
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Are negative delta G reactions reversible?
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Functionally, no.
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How is the equilibrium temperature determined?
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Set delta G to 0, plug in delta H and S, solve for T.
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What is the first law of thermodynamics
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All systems tend toward lower (more stable) energy states
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What is the second law of thermodynamics?
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Systems tend toward higher entropy
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Is delta G a fixed constant for a reaction?
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No, it varies with the reactant and product concentrations
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What is the chemical equilibrium point?
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A rxn will proceed until it has concentrations such that a <-> b, and delta G is zero in both directions; At that point no further net rxn occurs
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How do you know if a rxn is reversible?
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If the delta-G is small -> changing the reactant concentrations may reverse the sign of delta-G
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How do you know if a rxn is irreversible?
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If the delta-g is large. These reactions go almost to completion.
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Are hydrolytic rxns reversible?
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No.
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How are delta-G and Keq related?
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For a given reaction in given physical conditions, they are the same.
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What does delta-G0' mean?
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0 means all reactants are at 1M, except protons. ' means pH of 7
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What is the law of mass action?
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The rate of a chemical rxn is protiontal to the concentration of the reacting substances. As the reaction progresses forward, the concentration of products increases, and the reaction begins to move backward, and progresses to equilibrium.
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What does Keq reflect?
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The extent of a chemical reaction
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What does Kd reflect?
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The stability of noncovalent/weak binding of the interacting molecules -> a quantitative measure of binding affinity.
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What is the formulation for Keq?
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If aA+bB=xX+yY, then Keq=[A]^a*[B]^b/{[X]^x*[Y]^y}
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Is Keq dependent on the rate of the reaction?
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No, it is a fixed constant.
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How can delta-G0' be calculated from Keq and T?
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delta-G0'=-RT ln Leq, where R is the gas constant
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How does Keq relate to delta-G?
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The lower the equilibrium constant, the higher delta-G (if Keq=1 then ln Keq=0, and delta-G=0 -> equilibrium; Keq<1 -> ln Keq=-, so delta-G is +)
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How can the actual delta-G be calculated?
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delta-G=delta-G0'+RT ln Keq
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What 3 variables does the speed of a rxn depend upon?
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1) concentration of reactants 2) temp 3) presence/absence of catalyst
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What is Le Chatelier's Principle?
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If stress is applied to a rxn at equilibrium, the equalibrium is displaced in the direction that relieves the stress (e.g. pressure -> decreased ice formation)
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Describe the H2O/CO2/Bicarb buffer system in terms of Le Chatelier's principle
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In systemic capelaries, CO2 is high, leading to increased formation of H2CO3. In pulmonary capilaries, CO2 concentration is low, leading to the formation of CO2.
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Do catalysts speed up rxns only in one direction?
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No
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What do catalysts do?
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They lower the activation energy Ea
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Why do life forms need enzymes?
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Because the reactions to maintain life would not occur quickly enough w/out them (i.e. adaptation time)
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Why can't the temperature of rxns simply be increased to speed them up?
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Proteins/macromolecules would break down/denature; Also increases the speed of all reactions - no specificity
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Describe the properties of catalysts
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1) increase speed of rxns. 2) selective. 3) Don't change direction [delta-G] of rxn
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Do catalysts distinguish b/t stereoisomers?
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Yes
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What is good about Ea?
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If there was none, all reactions would have already taken place. No control would be possible.
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How does lowering Ea affect the rate of the reaction?
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It increases the number of molecules having sufficent energy to participate in the rxn, and thus [reactants] - this assumes normal distribution of kinetic energy in reactants
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What is a ligand?
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A small or large molecule or ion that the protein binds
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What is a substrate
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The particular ligand of an enzyme.
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What are the important functional regions of an active site?
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1) binding site 2) catalytic site [these may overlap]
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What stabalizes the bond b/t the active site and ligand?
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weak bonds (require close proximity)
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What 2 properties does the binding site have?
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1) specificity 2) affinity [Kd]
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What is an epitope?
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The particular region of an antigen to which an antibody binds
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What are CDRs?
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Complementarity determing regions - loops on the antibodies which determine epitope-binding.
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What is induced-fit theory?
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The substate interacts with reactive groups w/in the active site to change the conformation (tertiarty structure) of the enzyme which allows contact w/ the enzyme.
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How is metabolic regulation achieved w/ enzymes?
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By regulating the amount and/or activity of the enzymes
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What is allosterism?
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"another shape" of the enzyme d/t ligand binding. (thus ligands can be used to regulate the activity of enzymes)
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What are the three steps of enzyme-catalyzed reactions?
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1) binding of enzyme and its substrates 2) catalytic step 3) regeneration of the enzyme
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What is the turnover number of an enzyme?
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The number of substrae molecules converted to product per unit time.
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What is normally regulated in enzyme-catalyzed rxns?
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The first step (substrate binding)
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List the six major groups of enzymes
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1) oxio-reductases 2) transferases 3) hydrolases 4) lyases [add to =] 5) Isomerases 6) Ligases [formation of new bonds w/ ATP cleavage]
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What are cofactors?
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non-protein structures required for enzyme function
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What is a holoenzyme?
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The intact enzyme-cofactor complex [active]
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What is an apoenzyme?
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The remaining protein after cofactor removed [inactive]
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What is a prosthetic group?
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A coenzyme covalently bound to the holoenzyme [cannot dissociate]
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List two functions of metal ion cofactors
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1) bridging group to bring substrate/enzyme together 2) catalytic agent
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What do coenzymes do?
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Carriers of electrons, atoms + functional groups [e.g. Fe in Heme]
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Why are metabolic reactions often irreversible?
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They consist of long chains of reactions [pathways] with one irreversible [large delta-G] step, which acts as a "one way valve." These reactions may be reversed, but require different pathways.
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Why must there be irreversible pathways?
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1) otherwise amounts of reactants/products would always be at equilibrium 2) Allows control of metabolism (needed for homeostasis) [e.g. lactic acid formation/metabolism]. If pathways are controlled by different enzymes, we can simply control the enzymes.
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Why are chemical rxns in cells not at equilibrium?
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All products are reactants in another pathway. This leads to a steady state. Products are "pulled to the right", and intermediate concentrations do not rise, because they are being used for something else. This leads to greater efficiency [intermediates are used, as opposed to sitting around in equlibrium, and prevents high levels of toxic intermediates]
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