You lake your lac^- strain and transform in three different F^+ plasmids to cond

Question

You lake your lac^- strain and transform in three different F^+ plasmids to conduct a complementation test In the first experiment, your transform your lac^+ bacteria with a P plasmid that contains the entire lac operon from a normal (wild-type) strain In the second experiment, you transform your lac bacteria with a P plasmid that contains the lac operon form a strain missing the lacZ, gene {delta lacZ} In a third experiment you transform your What do you conclude front the previous experiment the lac^- strain has a recessive mutation in the lacZ gene lac^- bacteria with a F' plasmid that contains the lac operon from a strain missing the lacy gene (Delta lac Y). Table 1 below shows the results obtained when the transformatants were on plates with glucose or lactose as the sole carbone source. Table1,. Growth of lac-transformants on glucose and lactose plates. What do you conclude from the previous experiment? the lac^- strain has a dominant mutation in the locZ gene the lac^- strain has a recessive mutation in the lacY gene the Iac^- strain has a dominant mutation in the locY gene the lac^- strain has a mutation in the lac repressor that prevents it from binding lactose; the mutant repressor never stops repressing transcription of lac operon even in the presence of lactose Briefly define the following term auxotraph. Briefly define the following term autotroph Most cloning vectors are derived from Human chromosomes or mouse chromosomes Bacteria chromosomes or year chromosomes Plasmids or viruses. Transposes or plasmids e) Transposes or viruses.

Explanation / Answer

25.

in the first case, it is a wild type plasmid. therefore, it would produce beta galsctosidase and permease. thus it can grow on lactose medium.

in the second case, the plasmid is lacking lacZ gene. however, the repressor produced in plasmid can diffuse into bacteria and transcribe and translate lac Z gene of bacteria. but in this case, the bacteria were not able to grow on lactose, it is clear that bacteria has a mutation in lacZ gene.

in third case, repressor produced by plasmid diffused into bacteria. it allowed the bacteria to transcribe and translate permease that allowed lactose to enter bacterial cell. since the plasmid has functional beta galactosidase gene, it is capable of utlising lactose.

eventhough it is clear that mutation is in lacZ gene of bacteria but not in lacY gene of bacteria, we cannot conclude if the mutation is recessive or dominant. (as only three cases are given here).

26. auxotroph is a mutant organism that requires a specific nutrient to grow, which the strain could not produce.

or auxotroph is an organism that is mutant for a specific gene so that it is not able to synthesize that particular nutrient. therefore, if that specfc nutrient is supplied externally, it would grow. Otherwise it would not grow.

for example, histidine auxotrophs cannot synthesize histidine. therefore histidine must be supplied in the medium. otherwise, it would not grow.

27. autotroph is an organism that produces carbohydrates or its food by using sunlight (photoautotrophs) or by using chemical reactions (chemoautotrophs). they does not depend upon other organisms for food.

28. most cloning vectors are derived from viruses or plasmids. (since they are convenient to insert DNA molecules and are able to replicate themselves)

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