Toxic Plastic ■ 101division is more complicated than binary fission.
Eukaryotic DNA forms multiple, distinct linear
chromosomes wrapped around proteins and
coiled into fibers that have to be unwound,
replicated, and equally distributed between
the two daughter cells. In addition to the
multiple-chromosome problem, eukaryotic DNA
lies inside a nucleus, enclosed by a double layer
of membranes that make up the nuclear enve-
lope. In most eukaryotes, the nuclear enve-
lope must be disassembled in the dividing cell
and then reassembled in each of the daughter
cells toward the end of cell division. To make
things even more complicated, eukaryotic cells
undergo two types of division, depending on cell
type: asexual reproduction through mitosis, and
sexual reproduction—the production of sperm
and eggs—through meiosis.
Trade Secret
Back in Massachusetts, Soto and Sonnen-
schein spent 4 months trying to figure out why
their experiment had stopped working—how
unknown estrogen was getting into their cell
culture f lasks and causing the cells to divide.
By trial and error, they determined that a
compound seemed to be shedding from the
walls of the plastic tubes in which they stored
the liquid being added to the cell culture
flasks.
They called the tube manufacturer, who
confirmed that an ingredient was added to
make the tubes more impact resistant. But the
company refused to reveal the identity of the
“trade secret” ingredient. Soto and Sonnen-
schein spent a year purifying the secret ingre-
dient and finally identified a compound called
nonylphenol, a chemical used to make deter-
gents and hard plastics. The reason for all their
problems became clear: nonylphenol mimics the
action of estrogen.
Like estrogen, nonylphenol activates mitotic
division, a type of cell division that generates
two genetically identical daughter cells from a
single parent cell in eukaryotes. Mitotic division
consists of two steps that occur after interphase:
mitosis and cytokinesis. The first step, mitosis,
refers to the division of the copied chromosomes
in the nucleus. Mitosis is divided into four main
C
ancer accounts for almost 600,000 deaths in the United States
each year—nearly one in every four deaths. Only heart disease
kills more people. Over the course of a lifetime, an American male has
a nearly one in two chance of being diagnosed with cancer; American
women fare slightly better, with a one in three chance of developing
cancer. There are more than 200 different types of cancer, but the big
four—lung, prostate, breast, and colon cancers—combine to account
for about half of all cancers. More than 15 million Americans alive
today have been diagnosed with cancer and are either in remission or
undergoing treatment. The National Cancer Institute estimates that
the collective price tag for the various forms of cancer is more than
$100 billion per year.
Every cancer begins with a single rogue cell that starts dividing
without the checkpoints of a normal cell. This runaway cell division
rapidly creates a cell mass known as a tumor. Tumors that remain
confined to one site are benign. Because benign tumors can usually
be surgically removed, they are generally not a threat to the patient’s
survival. However, an actively growing benign tumor is like a cancer-in-
training. Because these tumor cells are not subject to the monitoring
that occurs at checkpoints during the cell cycle of a normal cell, their
descendants can become increasingly abnormal—changing shape,
increasing in size, and ultimately ceasing normal cell functions. As
tumor cells progress toward a cancerous state, they begin secreting
substances that cause angiogenesis, the formation of new blood
vessels. The resulting increase in blood supply to the tumor is important
for delivering nutrients to it and whisking waste away from it, allowing
the tumor to grow larger.
Most cells in the adult animal body are firmly anchored in
one place and will stop dividing if they are detached from their
surroundings—a phenomenon known as anchorage dependence. But
some tumor cells may acquire anchorage independence, the ability to
divide even when released from their attachment sites. When tumor
cells gain anchorage independence and start invading other tissues,
they are transformed into cancer cells, also known as malignant cells.
Cancer cells may break loose from their attachment sites and enter
blood or lymph vessels to emerge in distant locations throughout
the body, where they form new tumors. The spread of a disease from
one organ to another is known as metastasis. Metastasis typically
occurs at later stages in cancer development. Once a cancer has
metastasized to form tumors in multiple organs, it may be very difficult
to fight.
Cancer cells multiply rapidly wherever they establish themselves,
overrunning neighboring cells, monopolizing oxygen and nutrients,
and starving normal cells in the vicinity. Without restraints on their
growth and migration, cancer cells steadily destroy tissues, organs,
and organ systems. The normal function of these organs is then
seriously impaired, and cancer deaths are ultimately caused by the
failure of vital organs.