Cooperative Enzymes - This assignment was given by Susan Erster and this was a discussion board question and a sample question on test review exams PDF

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This assignment was given by Susan Erster and this was a discussion board question and a sample question on test review exams...

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A certain cooperative enzyme has four subunits, two of which are bound to substrate. Which of the following statements can be made? A. The affinity of the enzyme for the substrate has just increased. B. The affinity of the enzyme for the substrate has just decreased. C. The affinity of the enzyme for the substrate is at the average for this enzyme class. D. The affinity of the enzyme for the substrate is greater than with one substrate bound. Biological catalysts called enzymes aid in speeding up the rate of a chemical reaction without being consumed by the reaction itself. Without enzymes, the cell’s metabolic pathways would not be regulated at a proper rate. The way an enzyme functions is a substrate will enter the the active site on an enzyme held together by weak interactions. The complex formed through this process is called the enzyme-substrate complex (Erster Lect. 8). Cooperative enzymes fall under the category of allosteric regulation. Allosteric regulation is a term that describes a situation when a protein’s ability to function is compromised because another molecule has binded to another site on the same protein (Erster Lect. 8). Allosteric regulation can either cause an inhibit or activate an enzyme. Cooperative enzymes help to increase enzymatic activity by amplifying the response. As one binding site of a cooperative molecule gets filled, the affinity of the enzyme as a whole increases. (Campbell, pg.158). Choice A: It is unclear and inaccurate to claim the affinity of the enzyme has increased because we do not know what happened in the most recent reaction. The only information we know about the molecule is that there are two substrates bound to the enzyme. It is possible a substrate had disassociated previously causing the affinity of the enzyme to decrease thus making this answer choice incorrect. It is possible for the affinity to increase, but there is no way to claim it for sure. Choice B: This choice is also incorrect due to the same reasoning in Choice A. There is no way to determine if there had been another substrate bonded to the cooperative enzyme and whether it had disassociated or not. Since it is not clear if a substrate had disassociated, it is not true that the affinity of the enzyme decreased. Choice C: As more substrates bind to the enzyme, the affinity of the enzyme increases. However, the increase is not linear, thus the statement in this answer choice is not relatively true (Erster Lect. 8). It is known that when only one substrate is bound to the cooperative enzyme, the affinity is at its lowest. When all the active sites on the cooperative enzyme is bonded, the enzyme affinity is at its highest. But it is not true that affinity for this substrate is at average just because there are two substrates bonded to it. Choice D: This answer choice is correct because as mentioned before in the introducing paragraph, as the binding site of a cooperative enzyme is bonded to a substrate, the enzyme affinity increases. Thus, if the enzyme has two substrates bonded to the binding site, than the enzyme must be greater than the affinity of an enzyme with only one substrate bonded to the binding site (Erster Lect. 8).

A real life application of cooperative enzymes and allosteric regulation are in cytochromes P450 which have an important role in interactions such as drug to drug interactions. The experiment focused on functional cooperativity in the cytochrome P450 and its effect on enzymatic affinity in the protein. The cooperativity of the enzymes were tested using processes such as the stoichiometric ratio between a substrate and its effector. The results of the experiment showed the P450 enzymes do not rely on cooperative binding. Instead it proved the existence of a single binding site that has a greater affinity than a lone catalytic site. In essence the experiment highlighted the fact that functional cooperativity in the monomeric protein is not strongly needed (Denisov, pg 1). I agree with Alexander’s answer choice. I like his real life application that illustrated the use of cooperativity in HIV. I found it really interesting to see the fact that cooperativity helps to amplify response to enzymes can actually be a bad thing when it is mutated in HIV-1 protease because it becomes unlikely for the enzyme to be inhibited. Moreover, his reasoning for the answer choices were clear and direct as well. Works Cited: 1. Professor Erster’s Lecture 8 Notes 2. Reece, Jane B., Lisa A. Urry, Michael L. Cain, Steven Alexander. Wasserman, Peter V. Minorsky, Robert B. Jackson, and Neil A. Campbell. Campbell Biology. 10th ed. Glenview, IL: Pearson, 2014. Print. 3. Denisov, I. G., & Sligar, S. G. (2012, March 15). Review: A novel type of allosteric regulation: Functional cooperativity in monomeric proteins. Retrieved February 24, 2017, from ScienceDirect (10.1016/j.abb.2011.12.017)....