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56 Cards in this Set
- Front
- Back
RNA molecules that act like enzymes are called
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ribozymes
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# of substrate molecules converted to product per enzyme molecule per second =
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turnover number
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Define holoenzyme
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The "whole" enzyme, including cofactors
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Define apoenzyme
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the PROTEIN COMPONENT of a holoenzyme
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A loosely bound cofactor to an enzyme is called a
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coenzyme
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A tightly bound cofactor to an enzyme is called a
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prosthetic group
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Many coenzymes are derivatives of
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vitamins
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Proenzymes are
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inactive precursors of enzymes...are activated by cleaving off extra sequences
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Remember, enzymes ______ energy of activation but do not change ____
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-lower
-free energy difference between reactants and products |
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Enzymes can speed up a reaction by doing what actions to the enzyme substrate complex?
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-stabilize transition state complex
-form covalent intermediate -destabilize leaving groups |
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Why is substrate denatured?
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protein substrates are bulky and cannot fit into the active site. chymotrypsin must hydrolyze peptide bond on the carbon side of Phe, Tyr, or Trp so that the substrate can fit.
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Chymotrypsin hydrolyzes Phe, Tyr, or Trp. What do these enzymes have in common?
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They are all aromatic
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What amino acids make the catalytic triad?
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Aspartate-Histidine-Serine (D-Y-S)
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What amino acid is in the active site of gastric protease pepsin?
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aspartate
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Functional vitamin deficiency
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failure in transport system, inhibition of coenzyme synthesis
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which class of coenzymes forms a covalent bond with the substrate?
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activation-transfer coenzymes
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Thiamine pyrophosphate is a activation-transfer coenzyme that is used to cause _____________ reactions. thiamine deficiency is known as ___
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decarboxylation (breaking C-C bonds)
beriberi |
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PLP forms covalent interactions with ____________.
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amino acids
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Sulfhydryl group of CoA forms
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thioesters
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Biotin activates and transfers ___________ in __________ reactions
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CO2, carboxylation
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Oxidation-reduction coenzymes work with oxidoreductase enzymes. Examples include
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NAD+, FAD
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Do oxidation-reduction coenzymes form covalent bonds with substrates?
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NO
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Alcohol dehydrogenase oxidizes ethanol while its coenzyme, NAD+, gets reduced. ______________ is a product of ethanol oxidation and is responsible for alcoholic hepatitis.
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acetaldehyde
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Metal ions help bind coenzymes to the enzyme by binding their _________. ________ is usually bound to the enzyme through metal ions. They also bind anions.
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-phosphate groups
-ATP |
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Sarin gas is a ___________________ of acetylcholine esterase.
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covalent inhibitor
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Aspirin is a __________ of cyclooxygenase (COX), an enzyme involved in prostaglandin synthesis
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covalent inhibitor
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Penicillin is a ______________ that binds tightly to the enzyme necessary to form cell walls in bacteria, more tightly than any substrate or product can.
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transition state analog
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Allopurinol is a ______________ that binds tightly to xanthine oxidase to decrease urate production and thus treat gout
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transition state analog
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Heavy metals are toxic because they bind to the __________ or _______of many enzymes.
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SH groups
or functional metal ions |
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Michaelis-Menten equation:
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Vi: Vmax [S] / (Km + [S])
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Km is the....
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substrate concentration at half of the max velocity
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An enzyme with a small Km has a ______________ for that substrate
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high affinity
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An enzyme with a large Km has a ___________ for that substrate
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low affinity
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In the Lineweaver and Burk plot, the x intercept can be used to find Km. How?
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x intercept = -1/Km
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In the Lineweaver and Burk plot, the y intercept can be used to find Vmax. How?
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y intercept = 1/Vmax
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Why does hepatic glucokinase have a high Km?
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high Km = low affinity of glucokinase for glucose. That means you need large amounts of glucose for glucokinase to be effective. This is good in the liver because when you have high glucose, glucose gets phosphorylated into G6P and used by cells. When you have low amounts of glucose, you don't want cells to use up the remaining glucose. You want to increase blood sugar levels (glucose levels), not G6P levels. So hepatic glucokinase won't have a high affinity for glucose at low glucose concentrations (high Km).
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Why does hexokinase have a low Km?
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RBC has a high affinity (low Km) for hexokinase w/glucose because you need glucose to be metabolized to G6P right away for use, even with low amounts.
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Reversible enzyme inhibitors form what kind of bonds?
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noncovalent
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Competitive inhibition can be counteracted by
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high substrate concentration
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competitive inhibitors of cholesterol synthesis are
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statin drugs
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With competitive inhibition, what happens to Km and Vmax?
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velocity max does not change. However, now that you need more substrate to reach Vmax, Km (half Vmax) is increased.
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If you add an inhibitor to an enzymatic process that causes Vmax to increase, what kind of inhibitor did you add?
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a competitive inhibitor
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Noncompetitive inhibitors bind to ___________ sites on the enzyme
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different
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With noncompetitive inhibition, whathappens to Km and Vmax?
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Vmax decreases significantly. Km is unchanged (adding substrate has no effect)
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Allosteric enzymes have sites where allosteric inhibitors or activators cause
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conformational changes to enzyme
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Allosteric enzymes usually consist of multiple subunits and exhibit ___________ binding.
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cooperative
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In cooperative binding, the _____________ model is based on high cooperativity with all-or-none global states...the ___________ model shows one-by-one binding causing conformational changes in each subunit
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-concerted
-sequential |
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Allosteric regulators have some benefits over competitive/noncompetitive regulators:
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1. stronger effect
2. may act as activators because they don't occupy the active site 3. don't have to resemble substrate or product 4. fast acting |
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When you phosphorylate an enzyme, the target amino acids for phosphorylation are
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Ser
Thr Tyr |
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Protein Kinase A (PKA) is activated by
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cAMP
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Gproteins and PKA are regulated by
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protein protein interactions
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Precursors of proteases are called
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zymogens
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Trypsinogen is a zymogen that is cleaved by enteropeptidase to form ___________, the active enzyme
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trypsin
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What is the blood clotting zymogen cascade?
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prothrombin > thrombin digests fibrinogen > fibrin > clot formation
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phospholipase Cβ
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G protein activation
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the phospholipase Cγ
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fat/glycogen storage, activated by insulin in addition to MAP pathway and GLUT-4 going to membrane (to allow more glucose to enter cell)
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