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Lab Exercise 16/17 Study Guide

by: Kristi Crow

Lab Exercise 16/17 Study Guide BIO 221

Marketplace > Purdue University > Biology > BIO 221 > Lab Exercise 16 17 Study Guide
Kristi Crow
GPA 3.6

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Introduction to Microbiology
Dr. Tim Walters
Study Guide
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This 6 page Study Guide was uploaded by Kristi Crow on Sunday December 6, 2015. The Study Guide belongs to BIO 221 at Purdue University taught by Dr. Tim Walters in Fall 2015. Since its upload, it has received 12 views. For similar materials see Introduction to Microbiology in Biology at Purdue University.


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Date Created: 12/06/15
Exercise 16/17 Learning Objectives 1. Know which nucleotide bases are purines and which are pyrimidines 2. Define genotype and phenotype; wt and mutant; mutagenic factors; know different types  of mutations.  Genotype: genetic composition of an organism  Phenotype: observable property of an organism  Wildtype: organism without a change in the genetic code  Mutant: organism with a change in the genetic code  Mutagenic Factors: causes the mutation  Examples of different types of mutations:  o Harmful/lethal­ majority of mutations o Silent­ change in genotype/ no change in phenotype o Beneficial­ extremely rare 3. Understand the multiple effects of UV light on bacterial cell. Be able to explain their  mechanisms. Know what is the optimal wavelength of UV for killing bacteria and how it  works. 1. Deamination of cytosine ­ destabilize DNA molecule 2. Formation of thymine dimers (on same strand) 3. Distortion of double helix of DNA 4. Repairing Mechanisms: A) Photoreactivation (PR): enzymatic cleavage of thymine dimmers by PR  enzyme or photolyase; activated by visible light (300­600 nm); uses light as  energy B) Biochemical Excision Repair: excision of damaged bases; reconstruction of a functional DNA from undamaged fragments; hydrolysis of ATP for energy  A wavelength between 240­300nm is effective for killing bacteria but 260nm is the  optimal wavelength for killing bacteria by disorganizing the bacterial DNA. 4. Know 2 methods to repair thymine dimers and the difference between mechanisms. A) Photoreactivation (PR): enzymatic cleavage of thymine dimmers by PR enzyme or photolyase; activated by visible light (300­600 nm); uses light as energy; repairs the template and resumes normal functional template B) Biochemical Excision Repair: excision of damaged bases; reconstruction of a functional DNA from undamaged fragments; hydrolysis of ATP for energy;  repairs the template and resumes normal functional template 5. Understand the advantage that spore­forming bacteria have in relationship to UV light.  UV light has only limited applications for sterilization because it penetrates very  poorly. Spore formers like Bacilli are more resistant to UV light. So UV light can be  used for disinfection, not sterilization 6. Understand although UV light is damaging, why it is not always the best choice for  sterilization.  It penetrates very poorly, therefore spore formers are more resistant which is why UV  light can only be used for disinfection but not sterilization. Once spores are formed they  are resistant to heat, chemicals and even radiation. 7. Define symbiosis and symbionts. Know the 3 types of symbiotic relationships. Provide  the examples based on the human host – microbe interactions.  Symbiosis: living together  Symbionts: organisms which are living together in a particular environment   Commensalism: one organism benefits, another organism is not affected o Example: remora fish and sharks   Mutualism: both organisms derive benefit o Example: rumen bacteria and cows   Parasitism: one organism benefits at the expense of the other organism o Any microbial infection 8. Know the definition for the normal microflora. Explain the advantages and potential  disadvantages of having it.  Normal microflora:  normally present in and on the body (E. coli in an intestine, e.g.);  mutualistic relationships with a host; some members are able to cause an infection  (opportunistic pathogens).   Transient    microflora: microorganisms come and go, getting no benefits, and not  harming a host   Parasites: pathogenic microorganisms cause infectious diseases 9. Know what plants and bacteria can undergo nitrogen fixation.  Plants: leguminous (peas, beans, soybeans, alfalfas, clovers)  Bacteria: Rhizobium and Bradyrhizobium  The plant bacteria is an example of mutualism   Nitrogen fixation is ONLY possible if these organisms are co­existing 10. Know what type of symbiotic relationship between the Rhizobium bacteria and the  leguminous plants  Mutualism 11. Recall the process of nitrogen fixation, including the reactants, products, and enzymes  involved; the “oxygen dilemma” and how it can be solved in bacteria like Rhizobium.  Nitrogen fixation ­ an ability (extremely rare in nature!) to convert atmospheric N  to  2 ammonia.   Free­living (Azotobacter) and symbiotic (Rhizobium) bacteria capable of nitrogen  fixation   Rhizobium ­ Gram(­) rods when free­living; invades the root hairs of legumes via an  infection; converts to the bacteroid form and provides the host with ammonia, the plant  provides a shelter and nutrients (like carbohydrates) ­ mutualistic relationships   Nitrogenase and transaminase are two enzymes involved in nitrogen fixation; amino  acids and proteins are the end product of such reaction   Nitrogenase is affected by oxygen; oxygen is required for aerobic metabolism of  Rhizobium ­ the oxygen dilemma. It is solved by a co­production of leghemoglobin  (plants and bacteria produce different parts of its molecule), an enzyme that removes  oxygen from nodules.   


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