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© RCSB Protein Data Bank.

The picture here shows two different enzymes (purple) that read and replicate the DNA molecule (multi-colored). The enzyme on the right tightly encloses the DNA, and replicates it very accurately. The enzyme on the left has a loose active site that allows it to better accommodate the stiff thymine dimer shown in pink. The structure of the enzyme on the left allows it to do a better job of replicating damaged DNA at the cost of making more copying errors. When working with damaged DNA, the enzyme on the left works 3,000 times faster than the enzyme on the right. (Unit: 9)