DEC DINGCANCER HOW GOOD DNA GOES BAD
A
cell builds new DNA like zipping closed
well to subsequent tines, and the difficulty attaching the next
a winter coat, adding new zipper tines as the
building blocks sounds an alarm that signals the DNA polymerase
new DNA matches itself to the pattern DNA. But
enzymes that do the actual stacking to quickly fix the problem.
sometimes these two strands don’t stay perfectly zipped
And then even after DNA replication is finished, the new strand
together; sometimes they slip or wobble.
is compared to the old strand and any mismatched bulges or other
When the new strand slips, a little kink in the zipper can
abnormalities are pruned and repaired. Any errors that remain after
result in an extra nucleotide “tine.” When the pattern strand slips,
stacking and checking are coded into the DNA as mutations, but even
the kink can result in a missing nucleotide.
then cells with abnormal DNA aren’t likely to survive to replicate.
A wobble briefly makes a nucleotide “tine” on the pattern strand
Cells have to pass frequent tests of normalcy—like a Tour de France
able to grab a nucleotide tine other than its proper pairing—the
rider taking a drug test at the end of every stage—and cells that rush
wobble can insert the wrong nucleotide in the new strand. Most of
through their lifecycle like a doping rider aren’t allowed to continue.
these wobbles don’t last long—a mismatched tine doesn’t attach
Doping cells are pruned by apoptosis—programmed cell suicide.
NEW STRAND SLIP
PATTERN STRAND
PATTERN STRAND SLIP
NEW STRAND
PATTERN STRAND
NEW STRAND
MISMATCHED NUCLEOTIDE
EXTRA NUCLEOTIDE
MISSING NUCLEOTIDE
9 C3: WINTER 2012