when a negatively twisted covalently closed dna is annealed with single-stranded fragments of the same dna , under proper conditions a loop ( or loops ) may form by the disruption of a segment ( or segments ) of base pairs between the complementary strands of the covalently closed dna , and the formation of base pairs between the strands of the covalently closed dna and the single-stranded fragments .
C0012935
single-stranded
C0012854
dna