Topoisomerases are the enzymes
that wind and unwind the DNA
that makes up the chromosome
s. These enzymes work by altering the linking number
of DNA strands in a 3-step process:
- they break (cleave) one or both DNA strands
- they pass a DNA segment through the break
- they reseal the break.
Topoisomerases are important because the chromosomes must be unwound in order for the cell to use the genetic information to synthesize proteins
and to undergo replication
Thus, compounds like camptothecin that inhibit topoisomerase are useful in treating cancer. Topoisomerase inhibitors keep the chromosomes wound tight (the DNA is said to be supercoiled), and so the cell can't make proteins. As a result, the cell stops growing. Because cancer cells grow and reproduce at a much faster rate than normal cells, they are more vulnerable to topoisomerase inhibition than are normal cells.
This is based on work I did for the science dictionary at http://biotech.icmb.utexas.edu/