A comet assay is a technique used to determine the amount of double-strand breaks in DNA (DNA damage) in cells. The nucleus of an individual cell is placed on a microscope slide coated with an agarose gel. An electric
current is applied to the gel that causes DNA to move (electrophoresis), and the DNA is stained with a
fluorescent dye. When viewed using a microscope, undamaged DNA from the nucleus appears as a round shape
(the head), and the fragments of damaged DNA extend out from the head (the tail). The length of the tail
corresponds to the amount of the damage in the DNA (see Figure 1).
(a) To explain the movement of DNA fragments in the comet assay, identify one property of DNA and provide
reasoning to support how the property contributes to the movement during the comet assay technique.
(b) In a different experiment, cells are treated with a chemical mutagen that causes only nucleotide substitutions
in DNA. Predict the likely results of a comet assay for this treatment.

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.

During the process of blank and molecules such as a glucose must use a protein channel to cross through a cell membrane

The solution inside a plant cell is approximately a 1% saline solution and a 21% nacl solution the ,cytoplasm of a plant cell will