10.6: Summary

DNA is the genetic material of the cell. It’s made of two long strands joined along their length by the pairing of the four bases found in DNA. The segments that hold the directions to make protein are called genes (and only make up about 2% of our DNA). The sequence of bases in these segments provides the directions to make all the proteins in the body and, as such, the directions to reproduce the entire body.

Each gene provides directions to make a particular protein and occupies a precise location in DNA. All of the hereditary material in human DNA is collectively called the human genome, and includes about 20,000 protein-coding genes.

A biotech-produced protein can be made by inserting the gene for that protein into DNA of bacteria or cell cultures. These modified cells serve as protein- making factories, and the protein can be made in large amounts. Human insulin is one of the proteins made this way.

Mutations are changes in the bases in DNA. They can be spontaneous errors in DNA duplication or can be caused by substances called mutagens. An obvious impact of a mutation is its potential to change the instructions to make a protein. Mutations that occur in “germ cells” (cells holding the genetic material passed onto offspring, e.g., ova and sperm) are responsible for much of the genetic diversity among species, and are a major factor in adaptation and evolution.

Mutations are also responsible for genetically based diseases. Although mutations don’t necessarily cause cancer, many carcinogens (cancer-causing substances) can cause cancer by causing a mutation in a gene that regulates cell growth.

A virus is basically a short strand of RNA or DNA (a virus’s genetic material) enclosed in a protein coat. The coat allows it to get through a cell’s membrane (infect the cell). Once inside, the virus uses the cell’s ribosomes, enzymes, amino acids, etc., to reproduce. It can’t reproduce outside a cell.

Some viruses, such as HIV, are retroviruses. They carry special enzymes that enable them to incorporate their genetic material into the infected cell’s DNA. In this way, the directions to make the retrovirus becomes a permanent part of the cell’s own genetic material. This is why HIV infection has been incurable, although it’s treatable.

Viruses and bacteria have specialized tools useful for their own survival that biotech has put to use. In experiments to treat genetic diseases (diseases cause by defective genes), viruses have been used to insert the normal version of the gene into the patient’s cells. Enzymes from bacteria are used in DNA fingerprinting.

CRISPR-Cas9 is a powerful gene-editing technique based on a defense that bacteria use against viruses that infect them. It can be used in plants as well as animals, and has the potential to cure genetic diseases and cancers caused by specific mutations. Modifying plants by gene editing can have a big impact in agriculture. It’s unclear whether those who oppose GMOs will include those modified by CRISPR-Cas9.

DNA technology has exploded in many areas, most publicly in forensic science with genetic genealogy identifying criminals who committed crimes decades earlier. Many consumers have had their DNA analyzed and use the collective databases to create family trees. These same databases are useful in forensic science.