BSCI 222 – Principles of Genetics
Required Homework #9
Chapters 16 & 17 – Gene Expression
1. Indicate the phenotypes of the following E. coli lac partial diploids in terms of the active enzymes synthesized. With lactose?
a. I-P+O+Z+Y-/I+P-O+Z+Y+ -
b. I-P+OCZ+Y-/I+P+O+Z-Y+ +
d. I+P-OCZ+Y+/I-P+OC Z-Y-
2. Super-repressed mutants, IS, encode lac repressors that bind the operator but do not respond to the presence of inducer. Indicate the phenotypes of the following genotypes in terms of inducibility and enzyme production.
ISO+Z+ - The phenotype here is that the lac repressor cannot be removed from the operator so no induction of the lacZ gene.
ISOCZ+ - This has an OC so the lacZ will be constitutively expressed.
I+O+Z+/ ISO+Z+- Because the lac repressor can be used in trans, it does not have to be on the same DNA sequence as the gene it is repressing. No induction of the lacZ gene since IS cannot be removed by the inducer from the operator.
3. Define the following terms:
a. enhancer- sequence that stimulates maximal transcription of distant genes; affects only genes on the same DNA molecule (is cis acting), contains short consensus sequences, is not fixed in relation to the transcription start site, can stimulate almost any promoter in its vicinity, and may be upstream or downstream of the gene. The function of an enhancer is independent of sequence orientation b. response element-Common DNA sequence found upstream of some groups of eukaryotic genes. A regulator protein binds to a response element and stimulates the transcription of a gene. The enhancers allows a single factor to simultaneously stimulate the transcription of several genes. c. insulator- DNA sequence that blocks or insulates the...
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