answer all the questions : Microbiology case study about Evolution in Action: Th
ID: 204076 • Letter: A
Question
answer all the questions : Microbiology case study about Evolution in Action:The Power of Mutation in E. coli
Th e citrate (cit) operon
1. Operons are the basic unit of gene expression in prokaryotes. Explain the role of each of these operon components
in prokaryotic gene expression: structural genes, promoter, repressor, and operator.
2. Fully describe the E. coli cit operon as it functions in conditions without oxygen. Include promoter, repressor and
operator in your description.
3. The cit operon is under negative control. What does that mean and how is this operon negatively controlled?
4. What is the relationship between the cit operon and synthesis of the CitT transporter protein?
Genetic changes in the cit operon: Mutation
5. A section of the citrate operon, including the citT gene, was duplicated in an individual in fl ask #9. What precisely
was duplicated? What happened in terms of operon structure after this duplication?
6. How did this new arrangement facilitate the transcription of the citT primary transcript under conditions without oxygen?
How did this new arrangement facilitate the transcription of the citT primary transcript under conditions with oxygen?
7. Synthesis question: Explain the advantages and disadvantages of the citrate operon mutation in E. coli living in a fl
ask with E. coli that do not have this mutation.
Explanation / Answer
1. Structural gene: Contains those sequences of DNA that code for RNA and protein product.This is present downstream of promoter sequence and transcription is done by rna polymerase enzyme. Structural gene products mainly include enzyme and structural proteins.
Promoter: It is a short segment of DNA where rna polymerase binds and transcription starts. Promoter has consensus sequence which plays critical role in the binding of rna polymerase hollow enzyme. Strong promoter has exactly same concensus sequence so binding of rna polymerase is strong. But if the consensus sequence is not exact then different factors like up element, extended -10 sequence, discriminator sequence stabilize binding of rna polymerase enzyme. Thus expression of structural genes are under the control of promoter.
Operator: Operator or silencer is a short DNA sequence which has affinity for repressor protein. It can be present between promoter and structural genes or upstream or downstream of promoter sequence.
Repressor: Repressor is a protein that binds with operator. This is a trans acting factor and when bound to cis acting sequence (operator) decrease the rate of transcription or stop it. Thus regulation of transcription occurs.
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