BIO 2100 EXAM 6 (with solutions)

Describe how replica plating can be used to identify certain lac operon mutants correct answer Explain what a "constitutive" mutant is correct answer lost normal regulation, expressing genes for utilizing lactose even when not present/needed -detected by cleavege of B-galactosidase (ONPG) nitrogen group turned yellow -mutant organism that continuously produces a protein (may be produced in excess) due to mutation in regulatory gene, always expressed or impossible to turn off Explain how "partial diploid" mutants provide evidence for negative control acting through a combination of a protein (repressor) and a DNA sequence (operator) correct answer -add a properly regulated copy of the lac operon to constitutive mutants -some constitutive mutants did regain control -constitutive mutants generated independently did not regain control -negative control: one component diffusable within cell (protein, repressor), one component not diffusable within cell (DNA sequence, operator) -partial diploid mutants: bacteria made partially diploid (some genes have 2 copies) adding lac operon to constitutive mutant -many copies can diffuse around Define "operon" correct answer set of operator and promoter sites and the structural genes they control -in presence of glucose, lac operon not being stimulated -transcription Explain how, and why, glucose levels regulate expression of the lac operon correct answer -positive control (accelerator) -glucose present, CAP not active on operon -glucose absence, CAP active on operon Distinguish positive and negative control, and explain the value of the combination correct answer -negative control: repressor and operator, acting=on, not acting=off (protein known as repressor binds to DNA and blocks transcription) -positive control: CAP and CAP binding site (protein known as activator binds to DNA in order for transcription to take place) -evolved numerous strategies for regulating gene expression Relate environmental conditions to the state of the lac operon correct answer -cAMP active=no/low glucose -CAP not active=high glucose -absence of lactose would not express genes, repressor present -lac operon expressed when lactose is available and glucose is not