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6. Lecture Six - September 27.docx

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Jessica Hawthorn

EVOLUTION II A week from Wednesday is your first exam. Bring a pencil and an eraser. It is a scantron exam. You will be given a test booklet. Fill in the correct bubble on the scantron sheet. There‟s a lot of material in the book that is not covered in the class. I will not be emphasizing that material. So, where we left off, I had been talking about changes in O16 and O18 ratios in sedimentary rocks over time, and how we can use that to determine, amongst other things whether or not there are polar ice caps. Oxygen is so good at measuring temperatures that we can actually get exact numbers. We can get the average temperature of the oceans at a given point in time. What we know by looking at sedimentary rock records is that there have been multiple episodes where there has been no ice, as well long periods where there has been ice. Ice caps come and go. When we have polar ice, we call it an icehouse climate. When there is no polar ice, it is a greenhouse climate. Sea levels rise and fall as we go to and from icehouse and greenhouse environments. The Earth is warming up right now. So, is warming normal? Yeah, warming is normal, but you just don‟t lose as much polar ice as we have naturally within a few decades. The rate at which we‟re losing polar ice is hundreds of times faster than the fastest natural process. At this point, you have a general framework for the planet. There are some things to remember. It‟s a dynamic, recycling planet. Plate tectonics is driving continental motion, destroying continents and oceans, and also forming them. Organisms live on the surface of the planet, and respond to these tectonic changes over time. Essentially, as environments change, organisms adapt. Organisms can go extinct if they do not adapt. We have the geologic framework. What about the biologic framework. What is the evidence for evolution and the origin of life? Today, we‟re going to talk about the origin of life, and give an introduction to evolution. The best evidence for the origin of life is through one of the best scientific experiments ever conducted. Remember, science is all about experimentation. In 1953, Miller and Urey conducted a simple experiment to see what was required to form organic molecules through purely natural processes. Here‟s the thing: we all know that we‟re composed of amino acids. DNA is the backbone of the construction of our cells. Where do we get these amino acids? How do we form them? Miller and Urey took a big jar and they filled it full of the gasses that would have been present at the early stages of Earth‟s formation, prior to atmospheric oxygen. In one chamber, they created an atmosphere of hydrogen, methane, and ammonia. Below it was another chamber which collected any precipitates which formed. The scientists ran electricity through the atmosphere. They simulated lightning in an artificial environment. So, they zapped the atmospheric gasses with lightning. After one week of this experiment, four organic amino acids were spontaneously formed. In one week, Miller and Urey were able to spontaneously generate four amino acids. The earth is about 4.8 billion years old. In one week, four necessary amino acids for the origin of complex life were created. So, we learn that simple natural processes can create organic molecules from inorganic substance. That in itself is suggesting that natural processes can simply explain the origin of organic life. In one week, they started to build amino acids. The earth is the one place in the universe where we find organic molecules. However, it is not the only place. We also find them on meteorites. We also find them on Mars. These building blocks that are necessary for life are not restricted to Earth. They are simple formations. However, we (humans) are not just little bits floating around. We have complicated replicated structures. We need to have those amino acids turned into long repeated chains of amino acids. The amino acids need to become polymers. These include fats, sugars, proteins, enzymes, and everything else that your body is made up of. Your entire physical structure is made up polymers, organic polymers. Sydney Fox, another famous scientist, took a bunch of amino acids, and placed them under warm, dry conditions. They polymerized (formed complex chains of amino acids) spontaneously. So, for the two fundamental steps in creating organic material, it took three smart people with two experiments to generate the necessary amino acids and polymers for the origin of life. Now, we have nucleic acids that are polymerized, composed of amino acids that can form spontaneously. What about something as complex as a cell? Cells in living organisms are basically membranes surrounding an internal environment within which genetic material (either RNA or DNA) is replicated. Cells need a barrier between the internal and external environment. Water will dissolve a lot of nucleic acids. You need some form of membrane. This is done by polymerizing fats into fatty acids. Fatty acids have two different ends. They have a hydrophobic („water-fear‟) end and a hydrophilic („water-like‟) end. These fatty acids align themselves so that the two hydrophobic ends face each other, and the two hydrophilic ends face outwards. Hence, the barrier (the cell membrane) is two fatty acids thick. The hydrophilic ends face outward (one being exposed to the cell internal environment, and the other being exposed to the environment outside the cell). The hydrophobic ends face each other. Now, okay, we can spontaneously form amino acids. We can spontaneously polymerize amino acids into nuclear acids, and we can form fatty acids which go on to form membranes. What about something complicated like proteins? Here comes Sydney fox again. He generated proteinoids in his experiments. They‟re not alive. However, they do behave like certain living bacteria. They grow, spontaneously bud, and selectively absorb and emit certain chemicals. So, talk about life. When you go out in the world, you can see living things around you. There is a vast diversity of life. Fundamentally, there are three primary divisions. There is Eubacteria, Archaebacteria, and Eukaryotes. Eukaryotes are us, plants, and slime moulds. We all share a unique feature: a nuclear membrane, which protects the discrete nucleus in the cell. The genetic material is locked up in a separate environment in the nucleus. You will notice in this chart (in the professor’s notes) that there is an arrow linking Eubacteria with Eukaryotes. It connects mitochondria. We are not truly singular organisms. We‟re actually a composite organism. You do not have one DNA code for you. You have two. You have regular DNA and your mitochondrial DNA. In every cell, there are mitochondria. Basically, in the early evolution of eukaryotes, a symbiotic relationship develops where mitochondria provide energy to power the cells, coming from photosynthesis or respiration. So, every cell in your body has a eubacter
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