9a) Define operon. (2 points) b) How is the tryptophan operon regulated when try
ID: 254186 • Letter: 9
Question
9a) Define operon. (2 points) b) How is the tryptophan operon regulated when tryptophan level is high and low? ( c) Mutations have been identified that prevents the ability of a particular region region to form a stem-loop structure with a complementary region. Under th conditions, would attenuation occur? (3 points) Explain e fo Region 2 is mutant, tryptophan is low Region 3 is mutant, tryptophan is high Region 4 is mutant, tryptophan is low How is the tryptophan operon regulated under extreme starvation? (Explanation / Answer
Definition of Operon: Operons (clusters of co-regulated genes with related functions) are a well-known feature of prokaryotic genomes. Archeal and bacterial genomes generally contain a small number of highly conserved operons and a much larger number of unique or rare ones. The term “operon” was coined by Jacob and Monod [3–5], who characterized the first defined classical operon, the lac operon, in Escherichia coli. The lac operon consists of three structural genes that are required for lactose utilisation, lacZ, lacY, and lacA REGULATION OF trp Operon: Like regulation by the trp repressor, attenuation is a mechanism for reducing expression of the trp operon when levels of tryptophan are high. However, rather than blocking initiation of transcription, attenuation prevents completionof transcription. When levels of tryptophan are high, attenuation causes RNA polymerase to stop prematurely when it's transcribing the trp operon. Only a short, stubby mRNA is made, one that does not encode any tryptophan biosynthesis enzymes. Attenuation works through a mechanism that depends on coupling (the translation of an mRNA that is still in the process of being transcribed).
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