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10 Cards in this Set
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What are enzymes? • Biological catalysts that speed up reactions without being consumes •Lowers activation energy for reactions • DO NOT shift equilibrium, just reach it faster! • Very specific (tertiary/quaternary levels) • most are proteins Why does the body need enzymes? • Nearly all reactions require enzymes • Digestion & metabolism of carbs, fats & proteins |
What is the structure of an enzyme?
•globular •active site- where substrate fits •only one substrate will fit 1. How do enzymes work? 1. Enzymes contain an active site that reacts with a specific substrate E + S <-> ES <-> EP <-> E + P where: E = enzyme S = substrate E-S = enzyme-substrate complex E-P = enzyme-product complex P = product |
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What factors affect enzyme activity? |
1. How does temperature affect enzyme activity? 1. As the temperature increases so does the rate of enzyme catalyzed reaction • rate doubles every 10 C increase • denatures enzyme 2. Where is the peak activity? 2. Peak activity at the optimal temperature What does protein denaturation cause? Loss of structure and funcion |
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How does pH affect enzyme activity? Each enzyme has an optimum pH. This is where it will reach its peak activity. How do enzyme and substrate concentrations affect enzyme activity? If there is excess substrate the velocity of the reaction depends on [E]. What is an inhibitor? Anything that decreases enzyme activity! |
How do Cofactors and Coenzymes affect enzyme activity? Vitamin or mineral deficiencies will decrease enzyme activity. What affect do effectors have on enzyme activity? • Activators increase activity • Inhibitors decrease activity |
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Reversible inhibition: the stoppage of enzyme activity is temporary •most metabolic pathways are regulated: the cells control their out put & activity •Ex. hormones- usually only needed for a short time or in small amounts •the enzymes responsible for these pathways must be controlled •most metabolic pathways are regulated by some type of reversible reaction types of reversible inhibitors? • competitive inhibitor • non-competitive inhibitor |
Competitive inhibitor: A competitive inhibitor competes with the substrate for the active site of the enzyme
• energy conservation is important for cells, so in most pathways there is one enzyme that tends to be inhibited- usually on enzyme early in the pathway • often the final product is the inhibitor • it feeds & blocks the active site of the enzyme pathway • once the product is required again, the inhibitor releases from the active site & allows the pathway to start up again |
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Non-competitive inhibitor: A non-competitive inhibitor reacts with the enzyme-substrate complex, and slows the rate of reaction to form the enzyme-product complex. •the inhibitor (usually a product of the pathway) binds to the allosteric site of the enzyme •this binding changes the shape of the active site so the substance does not fit What is an allosteric site? The site other than the active site |
An irreversible inhibitor: permanent blockage of the enzymes activity •many toxins & poisons act in this manneri.e cytochrome cyanide |
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Compare and contrast how Competitive and Noncompetitive inhibitors affect enzymes. 1. Competitive: • If the enzyme binds to the inhibitor no product is formed • Vmax - no change • Km - larger (less affinity for binding) |
2. Noncompetitive Inhibitor: • The enzyme can bind to the substrate and then the inhibitor, or to the inhibitor and then to the substrate • Substrate binds to active site • Inhibitor binds to allosteric site • Vmax decreases (reducing the potential for product to be made) • Km - doesn't change |
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Activators: molecules or ions that promote enzyme activity •can bond to active site or allosteric site •they cause the substrate to fight tightly into the active site & increase enzyme activity |
What is the difference betweenCofactors and Coenzymes? Cofactors: • inorganic component needed to work •Minerals (Cu, Fe, Mg, Zn, Se) • usually metals ions or iron-sulfur clusters Coenzyme: • organic component needed to work (larger) • some bond permanently to enzymes: "prosthetic group" •other bind loosely & are not permanent: they leave the enzyme after the reaction is catalyzed |
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Enzyme Kinetics Models predict: • how the enzymes work • the role of enzymes in cellular activity • control/regulation (how) • how a drug might work on an enzyme • can also show: substrate affinity: how strongly or weakly the substrate binds to the enzyme * sequence of a substrate binding & product release (for multi0substrate binding enzyme)- Michaelis- Menten Plot |
1. Reaction velocity (Vo) 2. Maximum Velocity (Vmax) • the larger the better 3. Michaelis constant (Km) Affinity for binding (least amount needed for the reaction to happen) • amount of substrate required for 50% of enzyme to be bound • 1/2Vmax or 1/2 saturation • the smaller the better• 50% bound to substrate, 50% not = 1/2 efficient |
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What is the reactionvelocity dependent on: 1. [S] >> Km (leveling off near the Vmax) * inefficient enzyme: substrate does not bind tightly, enzyme catalyzes slowly 2. [S] > Km (between Vmax and 1/2 Vmax) * enzyme catalyze very fast |
1. Vo is dependent on [E] •enzyme is saturated with S • as [E] increases the amount of product increases 2. Vo is dependent on [E] and [S] • not completely saturated • as [E] & [S] increase so does the amount of product 3. Vo is dependent on [S] • as [S] increases so does the product |
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1. Smaller Km = high affinity tobind S (less [S] needed to reach 1/2 saturation 2. Larger Km = low affinity to bind S(more [S] needed to reach 1/2 saturation 3. Which is better? Smaller Km b/c lesssubstrate is needed to reach 1/2 saturation |
• as a substrate concentration increases, the velocity increases up to a certain concentration • the speed drops off until it reaches v.max (the fastest that an enzyme can work) • increasing substrate concentration does not affect the velocity |
