Concept explainers
Chapter 21 describes a blotting method known as Northern blotting, which can be used to detect RNA transcribed from a particular gene or a particular operon. In this method, a specific RNA is detected by using a short segment of cloned DNA as a probe. The DNA probe is complementary to the RNA that the researcher wishes to detect. After the probe DNA binds to the RNA within a blot of a gel, the RNA is visualized as a dark band. For example, a DNA probe complementary to the mRNA of the lac operon could be used to specifically detect the lac operon mRNA on a gel blot. As shown here, the method of Northern blotting can be used to determine the amount of a particular RNA transcribed under different types of growth conditions. In this Northern blot, bacteria containing a normal lac operon were grown under different types of conditions, and then the mRNA was isolated from the cells and subjected to Northern blotting, using a probe that is complementary to the mRNA of the lac operon.
Based on your understanding of the regulation of the lac operon, explain these results. Which is more effective at shutting down the lac operon, the binding of lac repressor or the removal of CAP? Explain your answer based on the results shown in the Northern blot.
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Genetics: Analysis and Principles
- A researcher was trying to determine whether two molecules(A nd B) were corepressors or inducers in their respective operon systems. Data was collected regarding the levels of protein and the amount of gene transcription for the genes in theri respectiver operons. The data is shown below. Level of protein Transcription of gene 1 low Transcription of gene 2 Molecule A High low Low high high Molecule B High high high Low low lowarrow_forwardDescribe what would happen to the lac operon in a low-lactose environment and in a high lactose environment. a) How will each of these environments affect gene expression? b) What would happen to the repressor in each case? c) How will each of these environments affect RNA polymerase?arrow_forwardTransformation is the process where bacteria take up a plasmid from the surrounding and then express the genes into proteins. Scientists only want the genes expressed at certain times, so they control the expression using the operon system. The arabinose operon is the classic system they use to control when the genes are to be expressed by the bacteria. Arabinose is a sugar that can be added to the agar plate that will turn on the operon. If arabinose is NOT present, no genes are expressed. A. What type of operon system is this? ____(negative controlled or positive) Explain _____ B. What type of gene regulation is this____ (inducible or irrepressible) Explain: ____arrow_forward
- A number of mutations affect the expression of the lac operon in E. coli. The genotypes of several E. coli strains are shown below. ("+" indicates a wild-type gene with normal function and "-" indicates a loss-of-function allele.) Please predict which of the following strains would have the highest beta-galactosidase enzyme activity, when grown in the lactose medium. O CAP+ r* p* o* z O CAP* I P* o* z* O CAP* r* P O* z* O CAP I P* O z*arrow_forwardThe map of the lac operon is shown below. Consider the following examples that include both haploids and partial diploids and explain in each scenario whether the repressor can bind and regulate expression and whether or not the lac operon is expressed. For partial diploids the plasmid is indicated by the F’. I+ O+ Z+ Y+ / F’ I+ O+ Z+ Y+ I- O+ Z+ Y+ / F’ I+ O+ Z+ Y+ I- O+ Z+ Y+ I+ Oc Z+ Y+arrow_forwardA number of mutations affect the expression of the lac operon in E. coli. Consider each genotype below and complete the table using “+” to indicate that the gene is expressed, and “−” to indicate that gene is not expressed.arrow_forward
- Northern blots are valuable tools to analyze the mRNA level present in a sample. Describe an experiment that uses the Northern blot as a tool and how you would visualize the mRNA giving at least two examples of probe types.arrow_forwardExplain how the lac operon can be used to express a recombinant protein in an E. coli cell. Explain why the B-galactosidase gene is made in two pieces with the a and 2 parts of the enzyme.arrow_forwardDraw out an example of a plasmid operon set up using amp resistance (outside the arabinose operon), arabinose operon with pglo genes embedded in the arabinose digesting enzyme genes. Remember to include the operator and promotor region.arrow_forward
- A lac operon containing one mutation was cloned into a plasmid, which was introduced by transformation into a bacterium containing a wild-type lac operon. The three genes of the chromosomal operon were rendered noninducible in the presence of the plasmid. (a) What kind of mutation in the plasmid operon could have this effect? (b) Suppose the result of transformation was to cause the three plasmid lac genes to be expressed constitutively, at a high level. What type of plasmid gene mutation could have this result?arrow_forwardA lac operon containing one mutation was cloned into a plasmid, which was introduced by transformation into a bacterium containing a wild-type lac operon. The three genes of the chromosomal operon were rendered nonin- ducible in the presence of the plasmid. (a) What kind of mutation in the plasmid operon could have this effect? (b) Suppose the result of transformation was to cause the three plasmid lac genes to be expressed constitutively, at a high level. What type of plasmid gene mutation could have this result?arrow_forwardExamine the following theoretical operon (gen) in E. coli which contains structural genes (genC, genB, genA) that are involved in amino acid biosynthesis. The gen operon also includes the gene encoding for the regulator molecule within it. When the amino acid that this operon helps synthesize is present, it binds to the regulator forming a complex which can bind to the operator region. Assume that the regulator molecule only binds to the operator in the presence of the amino acid. Promoter || Operator genC genB gen operon Regulator genAarrow_forward
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