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EB 2240 Exam I
| Question | Answer |
|---|---|
| Which statement about enzymes is NOT true? a) ES complexes b) lower Ea c) enzymes change Keq d) many enzymes change shape in ES complex e)rxn occur at "active site" in a precise 3D orientation of aa | c. enzymes DO NOT change the Keq for chemical rxns |
| To overcome an energy barrier between reactants and products, energy must be provided to get the rxn started. This energy, which is recovered as the rxn proceeds, is called what? | Activation Energy |
| As increased the concentration of the substrate, the rate of the rxn reaches a maximum, where further increases of substrate have little to no effect. Why? | Reaches saturation point--- all of the enzymes are bound to substrate |
| What are some characteristics about enzymes? | -can bind prosthetic groups such as metal ions that participate in enzyme -have defined buy static structures -bind their substrates at active sites -are compose primarily of polypeptides, which are polymers of amino acids |
| What happens to Km in non-competitive inhibition? | It stays constant. This is because Km represents the affinity of the enzyme and the substrate. This is not affected, however the efficiency of forming product is low. Inhibitor forms: E+I+S --> EIS --> no rxn instead of: E+S<-> ES -> E+P |
| What happens to the Vmax in non-competitive inhibition? | Vmax is decreased |
| What happens to Km in competitive inhibition? | It increases This is because it requires much more substrate [] to reach 1/2 the Vmax |
| What happens to the Vmax in competitive inhibition? | Vmax is unchanged |
| What is meant by saturation of the enzyme? | All enzymes are bound the substrate- it has reached maximum efficiency |
| How does the formation of an ES complex explain the reaching of a maximal velocity in the Vo and So graph? | The rate, Vmax, corresponds to the rate of formation of the product. And the ES complex is what the enzyme stabilizes (the transition state) |
| Explain mathematically how a value of Km can be obtained from the Vo vs S graph when Vo = 1/2 Vmax | Rearrange the Michaelis Menten Equation to solve for Km {Vo = (Vmax[S]/Km+[S])} |
| How does the M-M equation explain why the rate of an enzyme-catalyzed reaction reaches a Maximum value at a high substrate? | Because as the substrate increases, it will approach a large number divided by a the concentration +a small number; and will approach the same number |
| What is the chemical basis of enzyme specificity? | The active site is specific to certain chemical reactions/bonds |
| Describe generally what an enzyme-substrate complex "looks" like | Transition state |
| What is the chemical basis of enzyme catalysis? | Stabilize the transition state!/lowers the activation energy |
| Enzyme production is according to the body needs and is regulated through genes. In human body 2 types of enzymes are formed. What are they? What is their function? | Digestive and metabolic enzymes -Digestive: break down food into usable parts -Metabolic: catalyze biochemical rxns |
| Which of the following terms are used to describe the tendency of a rxn to occur when the substrates and products of the rxn are at any []? why? (a) delta G (b) delta G0 (c) -TdeltaS (d) delta H | delta G because delta G determines if the rxn is spontaneous or not |
| The cleavage of the high-energy bond of ATP into ADP and Pi is an example of what type of reaction? | Hydrolisis |
| Delta-G is negative, deltaG0 is positive. Will the reaction occur spontaneously? Why? | Yes, because DeltaG0 is at standard values only |
| Delta G is the... | Free energy of the products minus the free energy of the reactants |
| T or F: Delta G0 for a specific rxn can have many values | False |
| T or F: delta G refers to a specific rxn with fixed [] of substrate and products | True |
| T or F: delta G0 refers to a rxn at pH=7 and 25degrees Centigrade | True |
| T or F: Delta G and delta G0 can both have positive or negative values | True |
| What is an oversized lab notebook better? | It enables to paste in a standard size sheet of paper without concealing page & book numbers or signature blocks. |
| Why is a paginated lab notebook written in ink suggested? | Records are not washed away by an accident//proving in court such facts, as the idea of conception, model tests, and the test results//under U.S. patent law |
| What is an automatic pipette used for? | Conveniently and accurately drawing and delivering liquids in quantities ranging from about one micro liter to several milliliters. The pipette enables the operator to draw and deliver small quantities of liquids w/o exercising judgment or dexterity |
| A 20% glycerol solution can be made how? | 20 mL of absolute glycerol diluted to 100mL with water |
| Why does Km stay constant in non-competitive inhibition? | The inhibitor does not bind to the enzyme on the active site so does not effect the way the substrate interacts with it. Even though the shape of the active site has changed, and Vmax has decreased, the Km is still based on 1/2 the Vmax |
| When [S] = Km the velocity of an enzyme-catalyzed rxn is about | 1/2 Vmax |
| T or F: Living Organisms have the luxury of being able to increase and decrease temperature in order to affect the rate of biological rxns | True |
| If Km is unaffected an Vmax decreases it is ______ inhibition | Noncompetitive |
| T or F: kcat/KM - this ratio is often thought of as a measure of enzyme efficiency | False -- specificity |
| In class notes begin here- Define Enzyme | Biological Catalyst |
| T or F: Enzymes are faster than Catalysts | True |
| T or F: Enzymes are much larger than Catalysts | True |
| How many amino acid residues make up an active site? | 2-3 (out of the 1000s) |
| T or F: Enzymes work at extreme temperature, pressure, and pH compared to Catalysts | FALSE! |
| Describe specificity on enzymes | -Highly Specific -will not work w/o substrate -serteoisomers: chirality/achirality very important -very difficult to crystallize in the proper form |
| Where do Enzymes come from? | -Biological samples -genes cloned from other |
| Industry: Describe how Catalysts and Enzymes are used | Catalysts: Energy Processing Enzymes: Food Processing |
| Is the reversibility of a rxn absolute or arbitrary? | arbitrary-- immediately used for another rxn |
| what is Gibbs Free Energy? | deltaG0 = -RTln(Keq) deltaG0 = -RTln(products/reactants) e^(-deltaG0/RT) = Keq |
| Using the Gibbs Free energy equation... what does a (+) exponent tell you about a rxn? | That the deltaG0 value is negative and therefore the PRODUCTS will be favored |
| Using the Gibbs Free energy equation... what does a (-) exponent tell you about a rxn? | The deltaG0 value is positive and therefore the REACTANTS will be favored |
| Is deltaG0 a state or path function? | STATE FUNCTION!!! It is path independent, only initial and final location matter |
| What information can be inferred about the rate of a rxn from the deltaG0 value? | Nothing! The rates of rxns can be determined by the Ea (need to understand the transition state) THERMODYNAMICS TELLS US NOTHING ABOUT KINETICS |
| What information is needed to get information about the rate of a reaction? | The transition state! |
| How do catalysts work? | (1)Transition state needs to be attained - Ea to get there (2) Stabilize the TS |
| What is the deltaG of formation? | the deltaG of the reactants-->TS |
| What is the deltaG of Dissociation? | the deltaG of the TS-->Products |
| What is the total energy of a reaction (DeltaG) | deltaG = deltaGf + deltaGd |
| Can the number of T.S. be determined if the DeltaG of a rxn is given? | Nope :) |
| What is a branch of biochemistry that is a quantitative study of rxns catalyzed by enzymes | Enzyme Kinetics |
| What are the few ways Enzymes work? | (1)tweak the TS to lower its energy -stabilize it (2)destabalize the reactants (3)temporary formation of ES complex and providing an alternate pathway (4)reducing reaction entropy (5)increasing temperature |
| what is deltaH? | internal energy//determines endothermic or exothermic//state function |
| what is deltaS? | entropy//state function |
| what are some examples of roles on enzymes? | transporting O2 down bloodstream; digestion; production of hormones |
| what are the enzymes that are made of RNA called? | ribozymes (catalyze various rxns in organisms,mainly hydrolysis) |
| Applications of Enzymes | (a)Enzymes defects can cause disease (b)Genetic mutations and Viral/Bacterial infections can cause enzyme defects (c)Deficiency of Enzymes Quantity or defective or no Catalytic activity are two causes of defective enzymes |
| Is it possible for an enzyme to decrease a reaction rate? | Yes. This can occur sometimes in nature. |
| What happens to a catalyst at the end of a reaction? | It is regenerated in the last step even though in intermediate steps it had integrated with reactants |
| What are the 6 classifications of enzymes? | (1)oxioreductases (2)transferases (3)hydrolases (4)lyases (5)isomerases (6)ligases |
| what does biocatalysis have applications in? | food, feed, textile, leather, biofuel, cleaning detergents, paper, and the pharmaceutical industry |
| how do enzymes have application in diagnostics? | in medicine-- i.e. biomarkers |
| what are the two two proposed models of how enzymes work: | (1)the lock and key model (2)induced fit model |
| What are the Multiple Mechanisms to facilitate Catalysis? | 1. By proximity and orientation 2.By Acid Base Catalysis 3.By Strain Catalysis 4.By Covalent Catlysis |
| Why are enzymes so big? | (1)large shape helps the active site to be exact (2)regulation-inhibition and modification (3)targeting- where in the cell the enzyme is active (4)Conservation-evolution of enzymes;forming new enzymes from older proteins |
Created by:
savelae
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