DNase I cuts DNA that is not protected by bound proteins but is unable to cut DNA that is complexed with proteins. Human DNA is isolated, stripped of its nonhistone proteins, and mixed with DNase I. Samples are removed after 30 minutes, 1 hour, and 4 hours and run separately in gel electrophoresis. The resulting gel is stained to make all DNA fragments in it visible, and the results are shown in the figure. DNA fragment sizes in base pairs (bp) are estimated by the scale to the left of the gel. Examine the gel results and speculate why longer DNase I treatment produces different results.

Key Concepts

DNase I Function

DNase I is an enzyme that degrades DNA by cleaving the phosphodiester bonds between nucleotides. It specifically targets DNA that is not protected by proteins, meaning that when DNA is complexed with proteins, such as histones, DNase I cannot access and cut the DNA. Understanding this function is crucial for interpreting how varying treatment times with DNase I affect the resulting DNA fragments in gel electrophoresis.

Gel Electrophoresis

Gel electrophoresis is a laboratory technique used to separate DNA fragments based on their size. When an electric current is applied, smaller DNA fragments move faster through the gel matrix than larger ones, allowing for size estimation. Analyzing the gel results helps in understanding how the duration of DNase I treatment influences the size and quantity of DNA fragments produced.

Protein-DNA Interactions

Protein-DNA interactions are critical for various cellular processes, including gene regulation and DNA packaging. In the context of DNase I treatment, the presence of bound proteins can protect certain regions of DNA from enzymatic cleavage. As treatment time increases, more unprotected DNA may be degraded, leading to a change in the pattern of DNA fragments observed in the gel, which reflects the dynamics of these interactions.