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33 Cards in this Set
- Front
- Back
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How do enzymes speed up the rates of reactions?
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Lowers the activation energy of a reaction, but does NOT change free energy (delta G) and does NOT change the Keq (ratio of products to reactants)
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What determines the rate of a reaction?
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activation energy
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List the 6 categories of enzymes.
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LILOTH! lysase, isomerase, ligase, oxidoreductase, transferase, hydrolase
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What is a cofactor?
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Small molecules that enzymes depend on for catalytic activities that perform reactions that the enzymes can't do themselves
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What is a coenzyme?
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They are cofactors that make up 2 groups: metal ions and small organic molecules which many are derived from vitamins.
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What is a prosthetic group?
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It is a coenzyme that is tightly bound to an enzyme (ex FAD)
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How can enzymes catalyze reactions?
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1. be in close proximity or as a complex
2.multiple catalytic sites 3. for multiple catalytic sites enzymes have tunnels to allow intermediates to pass safely and stably |
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What is an example of a enzyme with multiple catalytic sites?
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fatty acid synthase
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What are the basic properties of enzymes?
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1. all are proteins (except species of RNA)
2. have bind sites (active or catalytic sites) 3. regulatory enzymes have allosteric sites 4. lowers activation energy 5. narrow functioning pH range 6. can increase temp to speed up reaction but can't increase the temp too much! 7. some require cofactors for activity 8. have 2 models for substrate binding |
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What are the two models for substrate bonding?
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Lock and key: enzyme has a binding site that specifically fits the substrate.
Induce fit: protein changes conformation to fit substrate |
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What is an example of an induce fit enzyme?
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Glucokinase (hexokinase) changes shape when glucose binds
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What are oxidoreductases?
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enzymes involved in oxidation-reduction rxn. ex) lactate dehydrogenase
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What are ligases?
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enzymes involved in ligation of two substrates at the expense of ATP. ex) Aminocyl tRNA synthetase
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What are isomerase?
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enzymes involved in isomerization. ex) triose phophate isomerase
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What are lyases?
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Enzymes that add or remove groups to form double bonds ex)furmarase
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What are transferase?
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Enzymes that transfer groups. Ex) NMP kinase
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What are hydrolases?
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Enzymes that perform hydrolase rxn (transfer of functional groups to water)
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How do you determine the maximum velocity of a rxn?
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Measure the initial velocity of a rxn and add increasing amount of substrate and measure the amount of substrate converted per minute
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How do you determine the initial velocity of a rxn?
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It is the slope of the curve of formation of product at the beginning of a rxn
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What is the typical curve of a Michaelis-Menten plot of velocity vs substrate concentration?
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hyberbolic
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What is Km?
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The substrate concentration at half-maximal velocity of a rxn. It is a constant for any given enzyme. Units: umoles/L or uM
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What is the relationship between substrate concentration and rxn velocity?
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proportional
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What is specific activity?
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amount of product produced/time/amount of protein which is a way to measure the purity of enzyme
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What are types of enzyme inhibition?
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Competitive, non-competitive, uncompetitive, allosteric modulations
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Describe competitive inhibition.
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Inhibitors that often are structurally similar to the substrate that compete for the same binding site. It increase Km but has NO EFFECT on Vmax. Inhibition can be overcome by adding more substrate
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Describe noncompetitive inhibition.
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inhibitors that bind to both the enzyme and enzyme-substrate complex. The Vmax is decreased but Km remains the same. This cannot be overcome by adding more substrate
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What is the Lineweaver-Burk Plot?
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1/v vs 1/[S]. Take the recipricol of the M-M equation give you 1/v=1/vmax + (Km/Vmax)(1/[S]). Used to determine Km (x-intercept) and the vmax (y-intercept) except take the reciprocal.
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What is an example of competitive inhibition?
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1. Methotrexate inhibits dihydrofolate reductase and prevents formation of tetrahydrofolate which is a coenzyme required for purine and pyrimidine synthesis which is used in chemotherapy to inhibit cell division.
2. STATINs mimic HMG-CoA to inhibit cholesterol synthesis to treat for hypercholestremia ex)lipitor 3. Ethanol is used to treat methanol poisoning. Instead of methanol converted to formaldehyde(=death) from alcohol dehydroenase, the enzyme reacts with ethanol which produces acetaldehyde. |
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What is an example of noncompetitive inhibitors?
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Acetazolamide is an inhibitor of carbonic anhydrase and is used as a diuretic agent like for glycoma patients
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What are properties of regulatory enzymes?
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1.irreversible rxns
2. multimeric 3.sigmoidal V vs [S] curves 4. cooperativity 5.positive and negative allosteric modifiers |
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What is positive and negative cooperation?
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Positive cooperation is when substrate binding to one subunit changes the conformation in a way that other subunits have a higher affinity to binding substrates. Negative cooperation is when substrate binding decreases the binding of other substrates.
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What are allosteric modifiers?
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Compounds that bind to a site other than the active site and regulate activity. A positive modifier decreases Km but a negative modifier increase Km
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Describe Hb and the Bohr Effect.
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Hb has 4 subunits (2 alpha and 2 beta) and 4 hemes that bind oxygen. The oxygen binding curve is sigmoidal and shifts to the right at lower pH and shifts to the left at higher pH. CO2 binds to Hb which lowers the affinity for oxygen to stay binding (happens in cappilaries) so oxygen is released to the tissues. But CO2 and H+ are release when the Hb reaches the lungs
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