Name___________________________ Section__________________ 7.014 Problem Set 1 Please print out this problem set and record your answers on the printed copy. Answers to this problem set are to be turned in to the box outside 68-120 by 5:00pm on Friday February 16, 2007. Problem sets will not be accepted late. Solutions will be posted online. 1. You are spending the summer working at the Venter Institute analyzing some of the new species collected during the voyage of the Sorcerer II. You are working on three single-celled organisms, currently identified as Species M, Species I and Species T. To begin characterizing these organisms, you want to determine how they obtain energy. (a) You first test for whether the organisms are heterotrophic or autotrophic. To do this, you grow all three species under different conditions. You first grow them in liquid media with light in a closed system that contains oxygen, nitrogen, phosphorous, all the salts in seawater, glucose and trace minerals. You also grow the three species in liquid media with light in a closed system that contains the same mixture described above, but this one has no glucose and is bubbled with CO2. You measure the growth of the three species over time by counting the number of cells at specific time points: With Glucose00.20.40.60.811.21.402468TimeConcentration of CellsMIT With CO200.20.40.60.811.202468TimeConcentration of CellsMIT Which of the species are heterotrophs and which are autotrophs? Explain how the data above helped you reach your conclusion. .Question 1 continued (b) You want to determine if the autotrophs are photoautotrophs or chemoautotrophs. To do this, you grow all species in liquid media, in a closed system, containing oxygen, nitrogen, carbon dioxide, phosphorous, all the salts in seawater, glucose and trace minerals. You perform the experiment twice, once with light and once without light. Light00.20.40.60.811.21.402468TimeConcentration of CellsMIT Dark00.20.40.60.811.21.402468TimeConcentration of CellsMIT Are any of the species photoautotrophs or chemotrophs? If so, explain how the data above helped you reach your conclusion. (c) Assume that you have identified a photoautotroph. You want to know if it is oxygenic or anoxygenic. Propose an experiment that would allow you to differentiate between these two possibilities.2. Energy metabolism and redox reactions. A partial list of the Standard E◦ values list from the Redox handout is reproduced at the end of the problem set. (a) “The decay food chain does not always function efficiently. Under certain circumstances it exhausts all the available oxygen. Decay is then incomplete; its products include methane, alcohols, amines, hydrogen sulfide and partially decomposed organic matter.” (i) What are the two predominant products of decomposition when oxygen is available? (ii) Does the above situation (decay in the absence of oxygen) describe decomposition in a reducing environment or an oxidizing environment? Why? (b) Over most of the last three billion years, photosynthesis has outpaced respiration on a global scale, as evidenced in part by the presence of forests fossil fuels and oxygen in our atmosphere. (i) Name the two chemical products of photosynthesis, and specify which one is a reducing agent and which one is an oxidizing agent. (ii) Predict the long term effect on 1) plant life and 2) other organisms on earth if respiration consistently outpaced photosynthesis on a global scale. (c) A schematic of the chemical, electron and energy flows in aerobic respiration is shown below. Note that this diagram does not reflect the exact stoichiometry of the reactions, just the flow of reactants, products and electrons (sold lines). Energy flows are shown as dotted lines. CO2glucose e-NAD+NADH+H+e-O2H2O ADP + PiH+ gradientATPQuestion 2 continuedraw a similar diagram for the metabolism of glucose by fermentation such that the products are ethanol and A schematic of the chemical, electron, and energy flows for one of many possible chemosynthesis ) Does the reaction in the dashed box create energy or use energy? Explain. i) Does the reaction in the solid box create energy or use energy? Explain. CO2glucose DCO2. (d)reactions is shown below: NO3- NO2- e-O2H2O (i (i NADPNADP+H+H+ADP + PiATPH gradient +e-NO3- NO2- e-3. Each of the macromolecules that we have discussed in class is made up of a type of building block and various types of bonds. (a) Fill in the chart below describing these properties for each of the macromolecules: Building Block Bond(s) Involved Carbohydrates DNA RNA Protein (b) When these building blocks are put together, a specific reaction occurs. What is the general name for this type of reaction? What product(s) are produced in each reaction in addition to the macromolecule? (c) DNA and RNA are both synthesized directionally, 5’ → 3’. To what do 5’ and 3’ refer? (d) Proteins are synthesized directionality: from the N-terminus to the C-terminus. To what do N-terminus and C-terminus refer? (e) The building blocks of carbohydrates can be referred to as α or as β. To what do α and β refer? 4. For each of the descriptions below, list what type of bond is being described, where you might expect to find that type of bond (in a biologically relevant molecule) and rank the strength of that bond in relation to the other types of bonds using 1, 2, 3 or 4 with 1 being the strongest bond. (a) This type of bond is the result of two particles of opposite charges being attracted to one another. (b) This type of bond is the result of the random fluctuations of charge within a molecule. These random fluctuations are a result of the movement of electrons and cause some regions of the molecule to be slightly negative and some regions to be slightly positive. This distribution of charge is known as a dipole. Two molecules can be attracted to each other due to opposing dipoles.Question 4 continued (c) This type of bond is the result of two atoms equally sharing electrons between them. (d) This type of bond is the result of unequal sharing of electrons within a molecule such that one region of the molecule is more electronegative than the other. The more electronegative region can then interact with the less electronegative region of another molecule. 5. To answer the question below, you
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