上海交通大学 考研 2008-2009微生物期末试卷答案Microsoft Word

上海交通大学 考研 2008-2009微生物期末试卷答案Microsoft Word 文档

Answer for Essay questions (30 points total)

1) Discuss the principle and basic process of penicillin selection method.(10 points)

Answer:

Principle 1: Nutritional Auxotrophs are at a disadvantage in competition with the parent cells, and so no direct way of isolating.

Principle 2: Penicillin kills only growing cells, and if penicillin is added to a medium lacking the growth factor, the parent cells will be killed, whereas the nongrowing mutant cells will be unaffected.

Key points for Process: After preliminary incubation, the population is washed free of penicillin and transferred to plates containing the growth factor.

2) Please give out some evidences of endosymbiosis theory. (10 points)

Answer:

1.Both chloroplasts and mitochondria contain ribosomes and they are prokaryotic type. Moreover, ribosomes from these organelles show rRNA sequences characteristic of specific Bacteria.

2.Mictochondria and chloroplasts contain small amounts of DNA arranged in a covalently closed, circular form, typical of prokaryotes.

3) Design an experiment for measuring the activity of

sulfur-oxidizing bacteria in soil. If only certain species of the

上海交通大学 考研 2008-2009微生物期末试卷答案Microsoft Word 文档

sulfur-oxidizers present were metabolically active, how could you tell/measure this? How would you prove that your activity measurement was due to biological activity? (10 points) The answer can be varied.

Example:

One could set up a soil microcosm containing H235S. The soil would be incubated with the radioisotope in place. After incubation, one could analyze the soil for the presence of 35SO42-, its presence indicating that sulfide oxidation had taken place. To insure that the oxidation was biological, one would sterilize the medium (soil) before adding the labeled H2S as a control, and if the activity measured in the experimental sample was biological, one should not see it in the control.