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Exam 2
| Question | Answer |
|---|---|
| Covalent Catalysis | Enzyme becomes temporarily covalently bound to the substrate to form a reactive intermediate |
| General acid-base catalysis | Involves catalytic transfer of a proton. |
| Metal Ion Catalysis | 1. Electrophilic to stabilize a (-) charge on a reaction intermediate. 2. Generate a nucleophile by increasing acidity of a nearby molecule. 3. Bind to the substrate to increase number of interactions with the enzyme and increase binding energy |
| Catalysis by approximation and orientation | Substrates are brought into proximity and oriented to facilitate the reaction |
| Competitive Inhibition | Prevents substrate from binding to the active site. Can overcome. Increases Km. |
| Uncompetitive Inhibition | Inhibitor combines only with the enzyme-substrate complex. Cannot be overcome. Decreases both Vmax and Km. |
| Noncompetitive Inhibition | Inhibitor decreases the turnover number. Cannot be overcome. Vmx is decreased and Km is unchanged. |
| Sequential reactions | Formation of a ternary complex consisting of the two substrates and the enzyme. |
| Double-displacement reactions (AKA Ping-pong reactions) | Formation of a substituted enzyme intermediate. |
| Allosteric enzymes | Regulate flux of biochemicals through metabolic pathways. Feedback inhibition. Catalyzes the committed step. |
| Feedback Inhibitors | DO NOT bind to active sites. They bind to a distinct regulatory site on the allosteric enzyme. |
| Positive Effector | Binds to the R form regulatory site, stabilizing and increasing R concentration back R and S interaction more likely. Shifts left. |
| Negative Effector | Binds to the T form, stabilizing and increasing the concentration of T, decreasing likelihood of R binding to an S. Shifts right. |
| Heterotropic Effects | Effects a substrate has on an allosteric enzyme. Shifts left or right. |
| 2 Properites of enzymes that make them useful catalysts | 1. Rate enhancement 2. Substrate specificity |
| Why are vitamins necessary for good health? | They are converted into coenzymes |
| Spontaneous Reaction | The reaction will release energy. This is exergonic. Delta G is negative. |
| Nonspontaneous Reaction | The reaction will use energy. This is endergonic. Delta G is positive. |
| 6 Major classes of enzymes | Oxidoreductase:transfer electrons Transferases:move functional groups Hydrolyases:Cleave bonds with H2O Lyases:Add atoms or functional groups to remove/form double bond Isomerases:Move functional groups WITHIN molecules Ligases:Join 2 molecules (ATP) |
| Cofactor | Coenzymes and Metals |
| Apoenzyme vs. Holoenzyme | Apoenzyme: Without a cofactor Holoenzyme: Complete catalytically active enzyme with cofactor. |
| What is Km and how is it related to E, S affinity? | Km is the substrate concentration at which an enzyme reaches half of its Vmax. The lower the Km, the higher the affinity of E and S. |
| What is the turnover number? | How many moles of a substrate are converted to a product per mole of enzyme in a defined time. K2=Kcat=Vmax/Etotal (s^-1) |
| Which of the following is true when comparing an uncatalyzed reaction to the same reaction with a catalyst? | The catalyzed reaction will have the same Delta G. |
| The lock and key analogy for enzymes applies to the specificity of enzymes | Binding to their substrate |
| Zinc, an essential trace element for most organisms, is present in the active site of the enzyme carboxypeptidase. The zinc most likely functions as ___ | A cofactor necessary for enzyme activity. |
| During a lab experiment, you discover that an enzyme-catalyzed reaction has a dental G of -20. If you double the amount of enzyme in the reaction, what will be the dental G for the new reaction? | Still -20 |
| Which of the following is a mechanism by which enzymes assist in formation of a transition state intermediate? | ALL OF THE ABOVE preventing interface by water. Positioning substrates in spatial relation with specific amino acid side changes. Binding substrate with high affinity and the product with low affinity. Playing a direct role in the reaction mechanism. |
| The amino acid shown below is histidine. The imadazole side chain of histidine can function in an enzyme active site as either a general acid catalyst or a general base. Which of the following is correct statement? | Within the range of physiological pH, the nitrogen in the ring can be easily protonated/deprotonated. |
| An enzyme will bind its substrate with high specificity due to: | A large number of weak interactions at the active site. |
| Classify phosphoenolpyruvate carboxykinase: | Lyase |
| Reaction-progress curves for two different reactions are shown below. Which of the following statements is true. | |
| Asparagine is required for cells to proliferate. It hydrolyzes asparagine to aspirate and ammonia. Treating patients with the enzyme asparaginase is sometimes used as a chemotherapy treatment. Shown below are Michaelis=Menten curves. Better one? | Asparaginase 2 (the lower one) |
| The x-intercept of a Lineweaver-Burk plot is: | -1/Km |
| The y-intercept of a Lineweaver-Burk plot is: | 1/Vmax |
| The x-axis of a Lineweaver-Burk plot is: | 1/[S] |
| The y-axis of a Lineweaver-Burk plot is: | 1/V |
| The turnover number for chymotrypsin is 100s-1, and for DNA polymerase it is 10s-1. Which of the following statement(s) is correct? | The velocities of the reactions catalyzed by both enzymes at saturating substrate levels could be made equal if 1- times more DNA polymerase was used as compared with chymotrypsin. |
| For a graph depicting Vo vs. substrate concentration for a Michaelis-Menten enzyme, Vmax is found: | At a substrate concentration that is much higher than the Km. |
| The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as: | Feedback Inhibition |
| A series of enzymes catalye the reaction X->Y->Z->A. A binds to the enzyme that converts X->Y at a position remote from its active site to decrease enzyme activity. Substance A functions as...? | An allosteric Inhibitor |
| An allosteric enzyme that follows the concerted mechanism has a T/R ratio of 100 in the absence of substrate. A mutation in the gene that encodes this enzyme results in an enzyme with a T/R ration of 0.01. How would this affect the substrate saturation? | BOTH A and B: Results in a hyperbolic curve and shows simple Michaelis-Menten kinetics |
| Parallel lines on a Lineweaver-Burk plot are diagnostic of a(n): | Uncompetitive inhibitor |
| The graph of kinetics on inhibitors is: | NONCOMPETITIVE INHIBITION |
| Some drugs used to treat HIV patients are competitive inhibitors of the HIV reverse transcriptase enzyme. Where in the reverse transcriptase enzyme would such amino acid a changes most likely occur in drug-resistant viruses. | In or near the active site |
| Penecillin is: | ALL OF THE ABOCE. irreversible enzyme inhibitor, inhibits an enzyme needed for cell wall synthesis ins gram negative bacteria. Binds covalently to its target and inactivates it. Acts as a suicide inhibitor. |
| Predict the effect of mutating the aspartic acid at the active site of chymotrypsin to asparagine | The mutant chymotrypsin will have VERY LOW ACTIVITY as compared to the normal chymotrypsin |
| Elastase, a protease that breaks down elastin, preferentially cleaves a peptide bond on the carboxyl site of lysine, alanine, and valine. This is because the specificity pock of elastase: | Has a small hydrophobic pocket, containing the amino acid residues valine and threonine. |
| In conducing an experiment with a new drug, you find that regardless of the concentration of substrate, the drug is able to inhibit the enzyme activity. From these data you know that the inhibitor is NOT: | Competitive |
| What factor(s) influence(s) the binding of oxygen to hemoglobin? | The partial pressure of oxygen, pO2 and the concentration of 2-3-BPG |
| Which of the following is correct concerning the differences between hemoglobin and myoglobin? | Hemoglobin exhibits cooperative binding of O2, while myoglobin does not. |
| When considering hemoglobin and oxygen transport, which of the following statements is correct? | The binding of each O2 molecules to hemoglobin increases its affinity for the next O2 molecules. |
| Myoglobin and hemoglobin are members of the same gene family. Which of the following descriptions of myoglobin is INCORRECT? | The diameter of the iron ion increases upon binding to oxygen. |
| An "internal reservoir" of oxygen in rested muscle is found in oxygen molecules bound to ___ | Myoglobin |
| In what way does hemoglobin act as a buffer against changes in blood pH? | Hemoglobin binds some of the excess protons released by carbonic acid |
| The structure of normal hemoglobin can be BEST described as: | A tetramer composed of two aB dimers |
| What accounts for the fact that fetal hemoglobin has a higher oxygen affinity than maternal hemoglobin? | It does not bind 2,3-BPG |
| The binding of 2,3-BPG to hemoglobin INCREASES its affinity for oxygen | FALSE |
| Who is(are) the author(s) of your textbook Biochemistry a short course? | Tymoczka, Berg, and Stryer |
| You have discovered an enzyme that can catalyze two different chemical reactions. Which of the following is most likely to be correct? | Either the enzyme has two distinct active sites or the reactants involved in the two reactions are ver similar in size and shape. |
| Succinylcholine is a fast acting, short duration muscle relaxant that is used when a tube is inserted into a patient's trachea and bronchi to look for signs of cancer. What will be the effect of this mutation on the patient? | The patient will clear the drug as at much slower rate, and paralysis time will be extended |
| Asparate transcarbamoylase is an allosteric enzyme and demonstrates a sigmoidal curve when Vp is plotted agains [S]. If CTP is a negative allosteric effector is added,... | The concentration of substrate necessary to reach on-half maximal velocity will increase. |
| The Bohr shift on the oxygen-hemoglobin dissociation curve is produced by changes in ___? | pH |
| Which of the following reactions prevails in red blood cells traveling through alveolar capillaries? (Hb=hemoglobin) | Hb+4O2 --> Hb(O2)4 |
| Hemoglobin | RBC protein that carries O2 from the lungs to the tissues. Cooperativity in O2 binding and release |
| Myoglobin | Binds oxygen in muscle cells. This is NOT cooperative. Single polypeptide chain. |
Created by:
jshaw14