Question

You treat a sample of DNA with DNase and run the digested fragments out on an electrophoretic gel. You found mostly long fragments. What can you conclude about this sample of DNA

Answer 1

The presence of mostly long fragments on the electrophoretic gel after DNase treatment indicates intact or minimally digested DNA, likely due to the absence of DNase restriction sites or incomplete enzyme activity.

Step-by-step explanation:

When a sample of DNA is treated with DNase and run on an electrophoretic gel, resulting in mostly long fragments, it suggests that the DNA did not contain a large number of restriction sites for the DNase or that the enzyme was not fully active. Gel electrophoresis allows separation of DNA fragments by size because DNA has a net negative charge and, when an electric field is applied, smaller fragments move faster through the gel matrix than larger ones. Therefore, mostly long fragments on the gel indicates intact or minimally digested DNA. If the DNA had been highly fragmented by the DNase, one would expect to see a smear representing a range of fragment sizes or more distinct bands corresponding to smaller fragments.

Answer 2

the sample contains mostly heterochromatin

Explanation:

Heterochromatin refers to a highly condensed state of DNA, whereas euchromatin is lightly packed. It is for that reason that heterochromatin is associated with a transcriptionally inactive state, whereas euchromatin regions are active for transcription. Heterochromatin regions resist DNases because these enzymes don't cut DNA randomly, but they show sequence preference. In consequence, highly repetitive DNA heterochromatin regions (e.g., centromeres, telomeres, etc) may exhibit resistance to DNA cleavage.