Cells of actively growing E. coli were incubated for several minutes with radiolabeled (radioactive) deoxyribonucleotides (dNTPs). The DNA was isolated from the cells, denatured into single strands, and separated according by size. The radioactivity in the tube corresponded to a single longer piece of DNA and a heterogeneous mixture of much shorter DNA fragments. Briefly explain what these two sizes of DNA fragments represent (two sentences).