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Sample/practice exam 2016, questions and answers
General, Organic & Biological Chemistry (CHEM1221)
University of Queensland
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Deep Thought Questions for Mini Test 1 1st Sem 2016 1. Cellulose and starch are both polymers of glucose but fulfil very different functions in cells. Explain the roles and properties of the two polymers and speculate which of their properties may have aided the evolution of their current function. Use the following terms in your explanation: Glycosidic Cell Energy storage. the glucose units in starch are connected alpha linkages, and that the glucose units in cellulose are connected beta linkages. Your body contains enzymes that will break starch down into glucose to fuel your body. But we humans have enzymes that can break down cellulose. Cellulose is a lot stronger than starch. Starch is practically useless as a material, but celluose is strong enough to make fibers from, and hence rope, clothing, etc. Cellulose dissolve in water the way starch will, and break down as easily. Breaking down or dissolving in water just would be a little too inconvenient for something we use to make clothes. Not to mention, a good soaking rain would wash away all the wooden houses, park benches, and playground equipment if cellulose were soluble in water. 2. Why do all cells need membranes, and why is it important that membranes are made out of phospholipids? Incorporate the following terms into your answer: semipermeable. Cell membranes protect and organize cells and regulates not only what enters the cell, but how much. cellular membranes are made of phospholipids, molecules composed of glycerol, a phosphate group, and two fatty acid chains. Glycerol is a molecule that functions as the backbone of these membrane lipids. Within an individual phospholipid, fatty acids are attached to the first and second carbons, and the phosphate group is attached to the third carbon of the glycerol backbone. Variable head groups are attached to the phosphate. models of these molecules reveal their cylindrical shape, a geometry that allows phospholipids to align to form broad sheets. their unique geometry causes them to aggregate into bilayers because they are molecules, with hydrophilic phosphate heads and hydrophobic hydrocarbon tails of fatty acids. In water, these molecules spontaneously align with their heads facing outward and their tails lining up in the interior. Thus, the hydrophilic heads of the phospholipids in a plasma membrane face both the cytoplasm and the exterior of the cell. Cell membranes serve as barriers and gatekeepers. They are Small hydrophobic molecules and gases like oxygen and carbon dioxide cross membranes rapidly. Small polar molecules, such as water and ethanol, can also pass through membranes, but they do so more slowly. On the other hand, cell membranes restrict diffusion of highly charged molecules, such as ions, and large molecules, such as sugars and amino acids. The passage of these molecules relies on specific transport proteins embedded in the membrane. 3. Protein structures are complex and described four different levels of complexity, primary, secondary, tertiary and quaternary structure. Describe each of these levels, and then speculate what would happen if ionic interactions and disulphide bonds were no longer available to stabilize the tertiary structure of a protein. Primary a single polypeptide chain. Secondary alpha helix structure or sheets. Tertiary R groups interact based on areas, polarity, bonding, etc. to form subunits. Quaternary the combination of multiple tertiary subunits. These shapes determine the function of the protein. The absence of ionic interactions would significantly change the gross conformation of the protein, meaning it would not function as intended as the proteins structure determines its use therefore without the structure from the ionic interactions and the disulphide bonds proteins lose their functionality. Compare it to the way proteins denature when the temperature pH are too extreme for the hydrogen bonds to work. All the bonding forces are important to making the structures exact and repeatable, even the relatively weak van der Waals forces. If any of them stopped working the proteins would unravel. 4. Could amino acids be used to form cell membranes if there were no phospholipids? Discuss. Although there are polar and amino acids which form the same idea as a phospholipid. While some amino acids are polar and some are they are just side chains. To have a hydrophilic external section you would need a backbone supported peptide bonding that faces inwards and allows the polar side chains to orient themselves outwards. Then for the hydrophobic internal section you need a backbone of peptide bonds to link amino acids together and orient inwards for a internal. It would therefore lack the selective permeability of the membrane and it maintain sufficient function to match a double membrane of phospholipids. 5. During his voyage to the Galapagos Islands, Darwin noticed that several closely related species of finches had slightly different beak structures, which favoured the use of different food sources. Based on this one observation, could you prove or disprove or theory of evolution? Would Lamarck have been able to use this observation to support his own theory of evolution use and disuse? What evidence would need to be observed in order to decide which theory was more accurate? 6. Mitochondria and chloroplasts contain small DNA molecules that encode some of the proteins needed in these organelles. Explain why this is the case and why other organelles (Golgi apparatus, endoplasmic reticulum) do not contain their own DNA. What other common feature of mitochondria and chloroplasts can be explained in the same way? Use terms such as: endosymbiont, bacteria, uptake, remaining DNA. This theory states that eukaryotic cells were formed prokaryotic cells going into a larger prokaryotic cell and then forming a mutualistic relationship (i. the smaller cell produced food for the larger cell, and the larger cell provided protection for the smaller cell, this created the chloroplast. 10. Why do endergonic reactions need to have an activation energy barrier? Why is the activation barrier beneficial when the products of the endergonic reactions are cellular components? The activation energy barrier is useful because all reactions are reversible. identical (but mirrored) in either direction, that includes the energy change and the activation energy barrier. Those graphs showing the energy change between the reactants and the products, and the activation energy barrier can read backwards if a reaction is run in reverse. The only thing stopping exergonic reactions from being completely spontaneous is the activation energy barrier. The activation energy barrier means that there needs to be a minimum level of energy associated with the molecule first before the reaction proceeds. Therefore, if you have an endergonic reaction that has no activation energy barrier, the products will spontaneously undergo an exergonic reaction thus always. The activation barrier exists so that the products of the endergonic reaction do not spontaneously undergo an exergonic reaction.
Sample/practice exam 2016, questions and answers
Course: General, Organic & Biological Chemistry (CHEM1221)
University: University of Queensland
