BIOCHEMISTRY ADDS TO THE 
14 
T he study of bio- 
chemistry goes 
back to Antoine 
Lavoisier, the 
18th-century 
French scientist who explained 
the role of oxygen in the 
metabolism of food to provide 
energy in both plants and 
animals, established the com- 
position of water and other 
compounds, and introduced 
methods of measuring aspects 
of chemical reactions, thereby 
laying the foundation for 
modern chemistry. 
In the 19th century, bio- 
chemists isolated and 
identified many cellular 
chemicals — for example, 
hemoglobin, the red pigment 
in blood, and chlorophyll, the 
green pigment in plants. They 
discovered that compounds 
taken from animal tissue 
consisted of many of the same 
chemical elements as nonliv- 
ing materials. They 
isolated the nucleic acids 
DNA and RNA, which are 
now known to govern heredity 
and protein synthesis. They 
began to study proteins, espe- 
cially enzymes, which catalyze 
chemical reactions in cells. 
When dealing with cells, the 
biochemists behaved quite 
unlike the microscopists, who 
had enormous respect for the 
details of the cell s structure. 
The biochemists simply 
ground up, or homogenized, 
large quantities of cells to 
release their contents into a 
solution and then analyzed 
the mixture (called the 
homogenate). Often, the 
homogenate was fractionated, 
or separated, into individual 
components. Usually this was 
done with a centrifuge, a 
machine that separates parti- 
cles according to their size 
and density by whirling them 
PICTURE 
around at high speeds. The 
largest and heaviest particles 
move to the bottom of the 
container most rapidly, fol- 
lowed by somewhat smaller 
and lighter components, until 
after a time there remain only 
the smallest and lightest 
particles at the top. 
In 1925, a Swede, Theodor 
Svedberg, developed an 
instrument that would prove 
at least as revolutionary as 
the electron microscope: the 
ultracentrifuge, a machine 
that could spin its samples at 
such high speeds and with 
such force (it could attain 
hundreds of thousands of 
times the force of gravity) 
that many of the smaller and 
lighter components of the cell 
and even proteins and nucleic 
acids could be collected 
separately and studied for the 
first time. 
