QuestionsSampleExam1_1

QuestionsSampleExam1_1 - Sample Questions For Exam 1 ...

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Unformatted text preview: Sample Questions For Exam 1 1. You have isolated a archeal species that lives in a hydrothermal vent at 90°C. You have determined that this archea has an S ­layer. You find that you can remove the S ­layer by treating the cells with a protease. To your surprise, you find that the S ­layer is not required for survival in low osmolarity (i.e. low solute concentration) environments. You hypothesize that the S ­layer is critical for these archeal cells to survive at the temperatures at which it grows, 90°C. Outline an experiment to test this hypothesis. Be sure to include a control in your experiment, and list the results you would expect if your hypothesis is correct. 2. You notice that there is a rod ­shaped bacterium present in the blood of the 10 sheep with a debilitating motor disease. This bacterium is not found in the blood of 10 sheep that do not have the motor disease. You name this bacterium S. motorus, and you suspect that it is responsible for causing the motor disease. You streak purify S. motorus, and inject a pure culture of this organism into 10 sheep that appear healthy. All 10 of the injected sheep develop the disease and you are able to re ­isolate S. motorus from 9 of the injected sheep. You conclude that S. motorus is the causative agent of the motor disease. You then find that another laboratory has data to support the motor disease being caused by a virus, not S. motorus. Indicate what is a possible flaw in your experimental technique that led you to incorrectly conclude that S. motorus is the causative agent of the motor disease. 3. You want to isolate a bacterium that uses cellulose as a carbon and energy source. You have a soil sample taken from a field with decaying plants. You hypothesize that your desired bacterium will be relatively rare in this sample. You design a defined growth medium whose only added source of carbon is cellulose. a) Indicate whether you would use a liquid or solid form of the growth medium to enrich for cellulose ­degrading bacteria and Why? b) You want to know whether the prokaryotic organisms you have isolated from your enrichment are Gram ­negative bacteria, Gram ­positive bacteria or Archea. Indicate what you would do to distinguish this? c) You determine that all the bacteria isolated are Geobacillus stearothermophilus. You want to know whether these are all the same strain of G. stearothermophilus or whether they are different. Outline a procedure to determine the relatedness of the different G. stearothermophilus isolates. d) G. stearothermophilus is a Gram ­positive bacterium, that you find is able to specifically adhere to cellulose. You hypothesize that G. stearothermophilus produces a protein to that specifically binds cellulose and that is responsible for mediating binding of G. stearothermophilus cell to cellulose. In which subcellular structure/location would you expect the cellulose adhesion molecule be located? (Choose one) 1. Cytoplasm 4. Periplasm 2. Cytoplasmic membrane 5. Outer membrane 3. Peptidoglycan e) You examine your G. stearothermophilus strains by transmission electron microscopy. You observe a structure outside of the presumed peptidoglycan layer that you hypothesize is a capsule. What test would you carry out to verify whether your G. stearothermophilus strain has a capsule? What result would you observe if your hypothesis is correct? 4. (Fill in the blank; one word answers) The function of the Gram ­negative bacterial lipoprotein is to cross ­links the outer membrane to the ______________ . Small molecules cross the outer membrane through ______________. 5. Many bacteria produce alcohols from sugar in the process of energy generation. These alcohols are toxic to cells. Alcohols can passively diffuse across a membrane, but several bacterial species have an antiporter to export alcohols. What advantage would having an alcohol ­specific antiporter provide for these bacteria versus those bacteria that simply relying on passive diffusion of alcohols across the membranes? 6. You have two different bacterial species that both utilize glucose as a sole carbon and energy source. Species A uses a PTS system transporter for glucose; whereas species B uses an ABC transporter for glucose. You mix a small, but equal numbers of cells together of species A and species B and grow them together in a defined medium with glucose as the sole carbon and energy source. You incubate this mixed culture to allow growth of the cells, at the end of growth do you expect: (choose one) a) equal numbers of species A and species B cells b) greater number of species A cells c) greater number of species B cells 7. You have two different bacterial species, one of which, species A, uses a symporter to transport glucose and the second of which, species B, uses an ABC transporter for glucose. You mix equal amounts of the species A and species B cells in a defined minimal medium containing 10 µM glucose (i.e. a low concentrations) as the sole carbon source. After incubation for several hours, would you expect to find: (Choose one) a) equal numbers of species A and species B cells b) greater number of species A cells c) greater number of species B cells 8. You have found that the soil bacterium, P. fluorescens, can use the pesticide KillX as a source of Nitrogen for growth. You hypothesize that KillX is actively transported into the cell. Outline an experiment to test your hypothesis. Be sure to include a control in your experiment. 9. You have isolated a new species of bacterium (K. pollutanti) from a site contaminated with trichloroethylene (TCE) and are able to grow it in pure culture. You examine K. pollutanti by electron microscopy and determine that it has flagella like those found on E. coli. You hypothesize that K. pollutanti is able to colonize TCE ­contaminated sites by chemotaxing toward TCE. Describe an experiment you would use to test your hypothesis that TCE acts as an attractant for K. pollutanti. Be sure to describe the result you expect if TCE is an attractant, as well as what you expect if it is a repellent or neither. Include a control. 10. Underline which of the following statements are true: If at the end of a run, an E. coli cell finds itself in a higher concentration of attractant than at the beginning of the run, the E. coli cell would always tumble and then run… a) …in the direction in which it is now pointed and for a shorter time period than the previous run. b) …in the direction in which it is now pointed and for a longer time period than the previous run. c) …in the same direction and for a longer time period than the previous run. d) …in the same direction and for a shorter time period than the previous run. 11. What is autotrophic growth? (Choose one answer.) a) growth using CH4 as the sole carbon source b) growth using CH4 as an electron donor for respiration c) growth using CH4 as an electron acceptor for respiration d) growth using CO2 as the sole carbon source e) growth using CO2 as an electron donor for respiration f) growth using CO2 as an electron acceptor for respiration 12. Nitrogen fixation and CO2 fixation are processes that lead to the conversion of inorganic molecules into biomass. Both these processes are energetically expensive, requiring a large number of ATP and reducing equivalents. List two general ways in which nitrogen fixation and CO2 fixation differ. 13. You inoculate a growth medium with equal numbers of an obligate heterotrophic bacterium and an obligate autotrophic bacterium. The only source of carbon or nitrogen in the growth medium is atmospheric CO2 and N2. The energy source of provided for the culture is light. At the end of the incubation period, you find that the numbers of both the heterotrophic bacterium and the autotrophic bacterium have increased. Speculate as to the carbon and nitrogen sources used by the heterotrophic bacterium for growth. 14. You have cultures that each have two species of microorganism present in them. One culture is an enrichment of an environmental sample for microorganisms that can utilize ethanol as a sole carbon source. The second culture is an enrichment of an environmental sample for microorganisms that can utilize butyrate as a sole carbon source. (Ethanol and butyrate are both common end-products of primary fermentation pathways.) For each culture, neither species present in the culture can grow using either ethanol or butyrate as the sole carbon source. You sequence the genes for the rRNA from present in the two cultures. The ethanol enrichment culture contains species you call Species A and Species B. The butyrate enrichment culture contains a Species C and Species B. Thus, in both cultures Species B is present. Assuming that Species B serves the same function in the growth of both the cultures, speculate as to the function at Species B may be serving for these cultures. 15. The organic carbon compound, glucose, is converted to an inorganic carbon compound under aerobic conditions and under anaerobic conditions even in the absence of any terminal electron acceptor for respiration. A. What are the inorganic carbon compounds that are the end-products of this conversion… Under aerobic conditions? Under anaerobic conditions? B. How many different organisms are required to convert glucose to the inorganic endproducts… Under aerobic conditions? Under anaerobic conditions? 16. Explain why is denitrification harmful to plant growth in agricultural settings? 17. Nitrification and denitrification serve a similar function for cells in allowing cell growth. What is this function? 18. Leguminous plants can form a symbiotic relationship with nitrogen-fixing species of rhizobacteria when N2 gas is the only form or nitrogen present. Given your knowledge of nitrogenase, indicate what is one critical environmental condition that the plant provides for the rhizobacteria to fix nitrogen and why this environmental condition is critical. 19. Describe the process of replication of the genome of a ssRNA( ­) virus including which enzyme(s) are involved in this process. 20. You are studying a newly discovered mammalian virus. In the viral particles, a ssRNA strand exists that has terminal repeats. What do these terminal repeats suggest about the class of virus to which this new virus belongs? a) Group I: dsDNA b) Group II: ssDNA c) Group III: dsRNA d) Group IV: ssRNA (+) e) Group V: ssRNA ( ­) f) Group VI: Retrovirus g) Group VII: dsDNA pararetrovirus 21. Which type of protein(s) is likely to be expressed late in the infection cycle of a virus (choose all that apply)? a) polymerase b) capsid protein c) lytic proteins d) maturation proteins 22. You have identified a new dsDNA virus. One of the putative proteins encoded by the genome is similar to proteins that are known to have DNA nicking activity. What do you propose the type of replication to be for this genome? 23. You have identified a new ssRNA( ­) virus of mammalian cells. One of the proteins you find in the viral particles is a RNA endonuclease. You propose a new mechanism for production of multiple proteins from a single ssRNA( ­) molecule – the endonuclease acts on the ssRNA (+) strands, created from the ssRNA ( ­) genome, to generate multiple ssRNA (+) fragments each of which will code for one protein. For this mechanism of multiple protein expression to work, what other functions will this virus need? 24. The ribosome ­binding site (RBS) for the maturation protein of an ssRNA (+) virus of a bacterium folds into a complicated stem ­loop structure that makes the RBS unavailable to ribosomes. Describe a mechanism that this virus may use to ensure that a small amount of the maturation protein is produced. ...
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This note was uploaded on 03/06/2012 for the course MIMG 100 taught by Professor Lazazzera during the Summer '10 term at UCLA.

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