Unwinding
of
the
Strand
in
Replication
The DNA double helix has to unwind in order to separate the two strands for replication. The T2
bacteriophage DNA molecule consists of about 200,000 nucleotide pairs and is about 70 microns in length. Since there are 10 base pairs per turn of the double helix, the molecule would have to undergo 20,000 rotations in unwinding during replication.
It therefore follows that replication must go on simultaneously with unwinding. It cannot wait for the complete unwinding of the DNA molecule.
The unwinding of the DNA double helix is brought about by DNA unwinding proteins (DNA binding proteins). The proteins bind preferentially to single strands of DNA and promote unwinding (denaturation) of double helical DNA.
