BMMAG_BMMSG 525 Microbiology I. Problem Set 2. The problem set is worth 20 point
ID: 187196 • Letter: B
Question
BMMAG_BMMSG 525 Microbiology I. Problem Set 2. The problem set is worth 20 points, divided as indicated below for each question. There is partial credit possible only for question 4c. 1. Create a line diagram of a gene with the following elements: promoter, operator, ribosome binding site, start codon, end codon, open reading frame, start of transcription, rho-independent transcription termination. Start with the arrow provided. Label where appropriate. (4 pts). 2. Transcribe the following sequence, and indicate all of the start and stop codons in all six frames (2 pts). 3. Translate the transcription (mRNA) sequence of the longest ORF in problem 2 (2 pts). 4. Assume a substitution mutation occurred near the beginning of the sequence, so that the DNA sequence is now: 3' TCACAATGAGCTCCCGATGAATCGGTGATCCGAAATCGGTCGC 5' a. What type of mutation has occurred (e.g. nonsense or missense, transition or transversion) (1 pt)? b. Does this sequence still have an ORF (1 pts)? c. Explain why or why not. (2 pts)? 5. Assume a second mutation occurred, such that the DNA sequence is now: 3' TCACAATGAGCTCCCGATGATCGGTGATCCGAAATCGGTCGC 5 a. What type of mutation has occurred (hint: it may not be the same as in problem 4) (1 pt)? b. If a peptide can be produced after this mutation, what is its amino acid sequence (2 pts) 6. The lac operon produces three proteins. From the genotypes below, state whether or not LacZ will be produced in the presence of allolactose and the absence of glucose (lacO is the primary lac operator). For a. through e. explain why LacZ will or will not be expressed. (1 pt each): a. Iacl., 1aco, lacZ-, lacY-, lacA+ b. Iacl+, 1aco, lacZ+, lacY-, lacA- c. lacl+, lacO, lacz+, lacY, lacA- d. laci-, laco, lacZ-, lacY+, lacA- e. lad», 1aco, lacZ+, lacY-, tacA+Explanation / Answer
Functions of the genes mentioned in the question are:
lacI- Gene for the repressor protein, it blocks the transcription of lacZYA in the absence of lactose.
lacO- codes for the operator protein which with the help of promoter helps the RNA polymerase to bind to the operon.
lacZ- codes for -galactosidase
lacY- codes for -galactoside permease
lacA- codes for -galactoside transacetylase
In (a), LacZ will not be expressed due to the presence of mutant lacZ gene, lacZ-, which cannot produce the protein -galactosidase.
In (b), lacO, means in the absence of the operator, the presence of wild-type lacZ gene will lead to the constitutive formation of LacZ Protein as the repressor(lacI+) cannot bind to the operator.
In (c), Here there is controlled production of LacZ protein in the presence of allolactose and absence of glucose. This is due to the presence of wild-type alleles of lacI, lacO, and lacZ. Since mutated lacY- and lacA- are present, their gene products would not be produced.
In (d), as in (a), LacZ will not be expressed due to the presence of mutant lacZ gene, lacZ-, which cannot produce the protein -galactosidase.
In (e) the absence of the operator (lacO), the presence of wild-type lacZ gene will lead to the constitutive formation of LacZ Protein as the repressor, formed from the gene lacI+, cannot bind to the operator.
Constitutive formation means lacZ gene products will be formed irrespective of the presence or absence of glucose/lactose.
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