Problem Set 3

Problem Set 3 - E25 Problem Set #3 Solutions Due 4/27/06...

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E25 Problem Set #3 Solutions Due 4/27/06 Please answer each question in under 50 words. If a question has a, b, c, you can use up to 50 words for each of these parts. Less is often better. #1 - 3 have to do with how cells regulate the expression level of their genes. The answers to #1 and #2 aren’t explicitly in the book – you have to think about them. #3 is in the book. 1. RNA is very unstable – it is easily broken down by the cell and often has very short lifetimes within the cell. (2 pts) a) Why do you think RNA evolved to be very unstable (ie why is it advantageous for living organisms to have RNA that can be easily degraded)? Hint: Think about what would happen if the RNA never degraded. RNA likely evolved to be very unstable to allow the cell to regulate the amounts of particular proteins present at different times. If RNA never degraded then translation of proteins could not be easily turned off and unnecessary proteins would be produced, draining the cell of energy and amino acids. b) Why do you think DNA evolved to be very stable? Hint: Think about what would happen if DNA degraded really quickly. DNA likely evolved to be stable since it encodes the genetic instructions for how an organism functions. DNA provides the framework for RNA transcription and protein translation which interact more directly in cellular activities. This framework must not be subject to degradation if an organism is to survive and produce progeny. 2. An operon is a set of bacterial genes that are transcribed on the same transcript (ie piece of mRNA). Genes that work together (for example many antibiotic synthesis genes) are often found together on the same operon. Why is it beneficial to the organism to have all of these genes on the same transcript as opposed to on several different transcripts? (1 pt) It is beneficial for an organism to organize genes that work together onto the same transcript (operon) so that it can more simply co-regulate the genes. Since the genes
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Problem Set 3 - E25 Problem Set #3 Solutions Due 4/27/06...

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