60 ■ CHAPTER 04 Life Is Cellular
CELLS
T
he sky was still dark when Daniel Gibson
hurried into the J. Craig Venter Insti-
tute (JCVI) in La Jolla, California. At
5:00 a.m., his footsteps echoed through the
empty halls of the building. He reached a labo-
ratory door and slipped inside. There, Gibson
peered into a warm incubator, his eyes scan-
ning rows of palm-sized petri dishes. His stom-
ach was in knots. For 3 months the experiment
had failed. Would this day—Monday, March 29,
2010—be any different?
Gibson is part of a team at the JCVI with a
single, audacious goal: to create life. For more
than a decade, this team of scientists and
engineers has attempted to build a synthetic,
or human-made, cell. Cells are the small-
est and most basic unit of life—microscopic,self-contained units enclosed by a protective
membrane (Figure 4.1). The human body is
composed of approximately 100 trillion (10^14 )
cells. On that day in 2010, however, the JCVI
was trying to synthesize just one cell—a single-
celled bacterium.
Gibson’s team had sequenced a bacterium’s
complete genetic information, its genome; built
a synthetic version of that genome using basic
laboratory chemicals; and, finally, replaced the
natural DNA of another species of bacterium
with the synthetic DNA. DNA (deoxyribonucleic
acid) is a large and complex molecule that acts
as a set of instructions for building an organism,
like a blueprint. Almost every cell of every living
organism contains DNA. DNA transfers infor-
mation from parents to offspring, which is why
it is essential for reproduction. Life, no matter
how simple or how complex, uses this inherited
genetic code to direct the structure, function,
and behavior of every cell. DNA is made up of
many nucleotides held together in a structure
called the double helix, a ladderlike assem-
bly twisted along its length into a spiral (see
Figure 3.11).
Gibson’s boss, the famous geneticist J. Craig
Venter, worked for more than 15 years and spent
millions of dollars to construct a synthetic DNA
helix from chemicals in the laboratory, but
Gibson and the team had been unable to get that
synthetic DNA to work inside a cell. Every Friday
for 3 months, they transplanted the synthetic
DNA into a bacterial cell whose own DNA had
been removed. The synthetic DNA included a
gene to make the cells turn bright blue, so every
Monday, Gibson hurried to the incubator and
checked the petri dishes for a colony of blue
cells. But Monday after Monday, the dishes were
barren. “We did the genome transplantation
again and again,” he recalls, “but nothing was
working.”
Then, in mid-March, Gibson identified an
error in a single gene in the synthetic DNA.
A gene is a segment of DNA that codes for a
distinct genetic characteristic, such as having
O-type blood or a dimpled chin. In Gibson’s
bacterium, the gene with the error was respon-
sible for DNA replication. When it wasn’t work-
ing, the bacterium couldn’t replicate its DNA,
and it died. So in late March, Gibson fixed the
DNA error, transplanted the genome yet again,
and waited.Figure 4.1
An individual organism may consist of a single cell or
many cells
All of these photos of cells were taken using electron microscope technology.
Color has been added to the images to differentiate structures within the cells.
Salmonella is a single-celled
bacterium that is a common
cause of food poisoning.This is one cell of the multicellular
plant Arabidopsis, which is used
extensively in genetic studies.Humans are multicellular
animals with many
specialized cells, such as
these neurons within the
central nervous system.Yeasts are
single-celled, but
more complex
than bacteria.
Some species are
critical for making
bread and beer,
while others are
pathogens.