4th_lecture - MCB 102 Professor Fyodor Urnov 06/24/10...

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MCB 102 Professor Fyodor Urnov 06/24/10 Lecture 4 ASUC Lecture Notes Online is the only authorized note-taking service at UC Berkeley. Do not share, copy, or illegally distribute (electronically or otherwise) these notes. Our student-run program depends on your individual subscription for its continued existence. These notes are copyrighted by the University of California and are for your personal use only. D O N O T C O P Y Sharing or copying these notes is illegal and could end note taking for this course. ANNOUNCEMENTS Starting this class, we will have poll questions that will be answered through clickers. You will not need to buy your own clicker as we will just be using the ones from the MCB department. We don’t have enough for the class but no points will be involved. The whole point is just to get a general idea of how the class is doing. If you don’t receive one, just cooperate with a neighbor. We will be passing them out at the doors in subsequent classes so you’ll get them at the start of class. The way that I will run the poll is that as long as 50% know the correct answer, I will not explain the answer in class. For those who don’t understand, it is up to you to learn the reasons for the answer at home. LECTURE As we extensively talked about last time, humans don’t decompose into dust while we’re still alive because we are a localized exception to the Second Law of Thermodynamics. We only manage to do this because entropy is ultimately gained somewhere outside of the localized exception. However, the processes needed to maintain our complexity are non-spontaneous. This brings us to a major issue: how can we perform the necessary reactions if they are non-spontaneous? Mother Nature has solved this by coupling the non-spontaneous reactions with other highly spontaneous ones , often the hydrolysis of ATP. A mechanical example of this same idea is a block sliding down a ramp providing the energy to slide another block up a hill. A mechanical example of energy coupling This can also be seen genetically in the synthesis of DNA from nucleic acids. This is obviously entropically unfavorable since you’re creating a complex, highly ordered structure from chaotic nucleic acids. Polymerization occurs because the precursors to the nucleic acids used are nuclei triphosphates which store energy the same way that ATP does (ATP is actually one kind of nuclei triphosphate). Enzymes Let’s now look at forest fires. When a tree burns, the carbon structures are oxidized into carbon dioxide. As we have mentioned before, the formation of CO 2 from organic compounds is spontaneous. So why don’t forests spontaneously combust? It is thermodynamically spontaneous, but there will always need to be some spark to start the fire. Likewise, the breakdown of sugar and oxygen is hugely thermodynamically favorable, which is why we have evolved to love sugar. This means that at equilibrium, the amount of carbon dioxide and
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MCB 102 ASUC Lecture Notes Online: Approved by the UC Board of Regents
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4th_lecture - MCB 102 Professor Fyodor Urnov 06/24/10...

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