In the absence of tryptophan, what happens to the genes within the trp operon? a) the regulator without tryptophan-binding prevents the genes from being transcribed. b) the regulator falls off the operator and structural genes get transcribed. c) lack of tryptophan increases the level of camp high, which leads to activation of cap protein and gene expression. d) the active repressor binds to the operator and genes do not get transcribed. e) the active activator binds to the operator and transcription of structural gene takes place.

Astudent from one of the research labs is having trouble preparing a slide for examination and photographing. the bacterial slide that he has brought to you was prepared using a commercially purchased stain. he has asked for your in determining what he is doing wrong so that he can change the lab protocols and continue on with his project. after examining the slide under oil immersion, you determine that no bacteria are present even though the student is able to show you the culture he used to make that slide that has visible growth in the liquid medium. which of the following statements does not explain the fact that there are no bacteria present on the student’s slide? by not allowing a glass slide to completely air dry before heat fixation, the flame will cause the surrounding water to boil and this will damage the bacterial cell. overheating during the fixation step boiled the water within the bacterial cells and resulted in the cells bursting. insufficient heating of the slide did not drive out the thin layer of water and this resulted in minimal bonding between the bacteria and the glass slide. rinsing with alcohol during the washing step stripped the bacteria off the glass slide. rinsing with alcohol during the washing step stripped the bacteria off the glass slide.