Labels:text | font | black and white | screenshot | typography OCR: Constructing recombinant DNA molecules requires the joining of DNA pieces from two different sources. Restriction enzymes, which cut DNA at specific sequences, are essential for this task. Several hundred restriction enzymes, each with a different target sequence, are known. The figure shows the cleavage of E. coli and human DNA by the enzyme EcoRI at its target se quence. When the DNA is cut, complementary single-stranded ends (called "sticky" ends) are produced. DNA from different sources cut with the same restriction enzyme have the same sticky ends and can therefore anneal with each other by base pairing to form hybrid molecules. The hybrids can then be linked permanently by DNA ligase.
