Following helicase treatment, the single-strand DNA is visually detected as separate from the double-strand DNA by non-denaturing PAGE electrophoresis. Following detection of the single-strand DNA, the amount of radioactive tag that is on the single-strand DNA is quantified to give a numerical value for the amount of double-strand DNA unwinding. 2. The DNA in Eukaryotic cells is coiled tightly around proteins called histones, which help in the tight packing of DNA. During interphase, the DNA is not tightly coiled into chromosomes, but exists as chromatin. 3. When preparing for nuclear division, during the S phase of interphase, the chromosomes copy themselves (i.e. DNA replication occurs).
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The first step in DNA replication is that the DNA double helix is unwound into two single strands by an enzyme called helicase. As explained in this video, one of these strands (called the “leading strand”) is continuously replicated in the "forward" direction while the other strand (“lagging strand”) needs to be replicated in chunks in the opposite direction.