assignment In the following three bacterial strains (A, B and C), the specified
ID: 262492 • Letter: A
Question
assignment
In the following three bacterial strains (A, B and C), the specified DNA regions are deleted.
Predict and explain the effect of the deletions in each strain regarding transcription of the genes
in lac operon in both absence and presence of the lac repressor signal molecule.
2) The following graph shows the growth of wild-type (ie, unpublished) bacteria that are grown
in a medium containing both glucose (low concentration) and lactose (high
concentration). The bacterial growth is plotted as a function of time in hours. One wants one
Explanation of the growth curve path with specific indication of what happens in the two phases
marked with Roman numerals, including a description of the source of energy the bacterium uses
in the two phases. Explain how this affects the transcription of the lac genes
in the two phases.
Explanation / Answer
1. The following are the effects of deletions in the given strains -
2. When a bacteria grows in a media with two metabolites and one of them is glucose, it begins its metabolism by first consuming glucose. Once the glucose is all used up, it starts using the second metabolite. Here it is another sugar called Lactose. The metabolism of lactose is controlled by the lac operon, a set of genes that produce the enzyme beta galactosidase which breaks and consumes lactose into its constitiuent sugars. In the presence of glucose, the lac operon remains deactivated and the bacteria focuses only on the consumption of glucose. In the given graph, Phase 1 shows the growth of bacterium under glucose metabolism, the bacterial cell populations increases exponentially with time and comes to a halt when al the glucose is consumed. In the absencce of glucose, the lac operon is activated and upon the production of beta-galactosidase, starts the metabolism of lactose. Phase II shows bacterial growth under lactose metabolism, the cell numbers continue to grow from where they left off at the end of glucose metabolism. However, the process of lactose metabolism is slow and the increase in the bacterial population is also slow in phase II (as shown by the less steeper curve). In phase I the lac genes were inactivated due to the presence of excess glucose which binds to the catabolite activator protein (CAP). When no glucose is present, CAP binds to the lac operon and starts the metabolism of lactose. In addition, lactose permease enzyme is also inactive which transports lactose inside the cell. Once glucose is consumed (phase II), CAP initiates the lac operon and lactose permease starts the transport of lactose inside the cell for metabolism.
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