DNA is a lengthy molecule — approximately 1,000-fold longer than the cell in which it resides — so it can’t be jammed in haphazardly. Rather, it must be neatly organized so proteins involved in critical processes can access the information contained in its nucleotide bases. Think of the double helix like a pair of shoe laces twisted together, coiled upon themselves again and again to make the molecule even more compact.
However, when it comes time for cell division, this supercoiled nature makes it difficult for proteins involved in DNA replication to access the strands, separate them, and copy them so one DNA molecule can become two.
Replication begins at specific regions of the chromosome where specialized proteins separate the two strands, pulling apart the double helix as you would the two shoe laces. However, this local separation actually tangles the rest of the molecule further, and without intervention creates a buildup of tension, stalling replication. Enter the...
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