238 Green Chemistry, 2nd ed
is still not known for most organisms. Original estimates of the number of genes in
human DNA were in excess of 100,000, but extensive investigation of human DNA
now indicates that it may be only 30,000, or even fewer (much to the disappointment
of venture capitalists who financed human DNA studies with the prospect of patenting
large numbers of human genes.)
Proteins are the biological molecules that make up much of the structure of cells
and that perform most of the key functions of living organisms. Proteins are made
according to directions provided by cellular DNA. The steps in protein synthesis are the
following:
- The DNA in a gene that is specific for a particular protein transfers information
for the protein synthesis to RNA. - The RNA links with a cell ribosome, which is the protein-synthesizing entity
of the cell. - Using directions provided by the RNA, the ribosome assembles amino acids
into a protein. - The protein performs the function for which it is designed in the organism; for
example, it may function as an enzyme to carry out metabolic processes.
As the entities that give the directions for protein synthesis, genes are obviously
of the utmost importance in living organisms. As discussed in Section 9.8, genes can
now be transferred between different kinds of organisms and will direct the synthesis
of the protein for which they are designed in the recipient organism. It is now known
that a number of human diseases are the result of defective genes, and there is a genetic
tendency toward getting other kinds of diseases. For example, certain gene characteristics
are involved in susceptibility to breast cancer.
Because of the known relationship of gene characteristics to disease, the decision
was made in the mid-1980s to map all the genes in the human body. This collective body
of genes is called the human genome and the project to map it is called the Human
Genome Project. The original impetus for this project in the U. S. arose because of
interest in the damage to human DNA by radiation, such as that from nuclear weapons.
But, from the beginning, it was recognized that the project had enormous commercial
potential, especially in the pharmaceutical industry, and could be very valuable in human
health.
The sequencing of the human genome has been done on individual chromosomes.
Each chromosome consists of about 50 million base pairs (see Figure 9.6). However,
it is possible to sequence only about 500-800 base pairs at one time, so the DNA has
to be broken into segments for sequencing. There are two approaches to doing this.
The publicly funded consortium working on the human genome project identified short
marker sequences on the DNA that could be recognized in reassembling the information
from the sequencing. The private concern involved in the effort used a process in which