DECODING THE MASTER PLAN
At the dawn of the 21st century, the Human Genome Project had just been completed. This revolutionary undertaking—determining the exact size, sequence, and location of genes within the human genome, or the full complement of DNA in each of our cells—is one of biology’s most outstanding achievements. For the first time, researchers possessed the complete human blueprint. Ideally, they could now pinpoint the source of countless diseases. This ushered in what many, including the European Commission and the National Academy of Sciences, have referred to as the Century of Biology. Since then, the ability to quickly and economically sequence the human genome has increased exponentially, and the first truly complete human genome sequence was produced in March 2022.
DNA is the blueprint of this Century of Biology. Found in all living cells, DNA is the genetic material that stores and transfers information. In this chapter, we look deep inside the cell and examine the molecule upon which the entire biotechnology industry rests, starting with key discoveries and the scientists behind them.
THE STORY OF DNA
In the 1850s, an Austrian monk named Gregor Mendel performed breeding experiments with pea plants. He observed that specific genetic characteristics were passed down from one generation to the next in specific ratios. Mendel is considered the father of genetics because he was the first to analyze the inheritance of traits systematically. Mendel’s contributions are even more impressive because he didn’t know about DNA and predicted its existence. He called what we know now as DNA “particles of inheritance,” which he suspected were responsible for passing traits from generation to generation.
Almost a century later, in 1944, scientists identified DNA as the “particles of inheritance.” The race was then on to determine its structure. Eventually, the research team of James Watson and Francis Crick solved this scientific puzzle in 1953. The structure that Crick and Watson conceived was a double helix. An X-ray image captured by English chemist Rosalind Franklin revealed that DNA was helical. Sadly, Franklin died before receiving full credit for her critical contribution. Scientists have proposed many other possible configurations, including a triple helix. However, only the double helix model fits the evidence of base pairing provided by Erwin Chargoff.
The last sentence of Watson and Crick’s Nature paper, which described the double helix structure, made a critical point: “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” This suggestion would have profound implications for the as-yet-unrealized field of biotechnology.
LIFE’S BUILDING BLOCKS
The full name for DNA is DeoxyriboNucleic Acid. It’s a long molecule classified as a nucleic acid because it is
made up of repeating subunits called nucleotides. Each of the four DNA nucleotides consists of three parts: a sugar, a phosphate group, and a base. The prefix “deoxy” means “without oxygen.” It refers to the lack of an oxygen molecule at a particular spot in the sugar molecule. “Ribo” stands for ribose, which is a type of sugar.
All DNA, found in all living things, use the same four bases called thymine (T), adenine (A), cytosine (C), guanine (G), and the same sugar and phosphate molecules. Incredibly, the nucleotide building blocks for the genetic material of all forms of life are identical. However, the bases are ordered differently in each. Their order is the DNA sequence. Every organism, from yeast to sugar cane to giraffes, has a unique DNA sequence.
In the early aughts, the Human Genome Project was completed, revealing humanity’s genetic map and paving the way to identify diseases. This scientific endeavor marked the start of the Century of Biology, a period of international collaboration in the life sciences. DNA is the genetic material that stores and transfers information so our bodies can function; it is the essential code within cells. This excerpt from The Biotech Primer One: The Science Driving Biopharma Explained traces this journey from Mendel’s pea experiments to Watson and Crick’s DNA discovery, which hinted at revolutionary biotechnology potential. To learn how DNA is used in diagnostics to identify disease and used in gene therapy to cure disease, consider taking one of Biotech Primer’s many on-demand classes.
FREQUENTLY ASKED QUESTIONS
1. WHAT ARE THE BUILDING BLOCKS OF DNA?
DNA is composed of repeating subunits called nucleotides. Each nucleotide consists of three parts: a sugar molecule (deoxyribose), a phosphate molecule, and a base. The four bases are adenine (A), cytosine (C), guanine (G), and thymine (T).
2. WHO ARE THE PIONEERS IN THE STUDY OF DNA?
The study of DNA saw significant contributions from Gregor Mendel, who is considered the father of genetics. Later, James Watson, Francis Crick, and Rosalind Franklin played pivotal roles in determining the double helix structure of DNA.
3. HOW DOES DNA FORM ITS DOUBLE HELIX STRUCTURE?
Nucleotides link to form a long chain with a sugar-phosphate backbone. Within a DNA molecule, Cs on one strand are matched to Gs on the opposite strand, and As on one strand are paired with Ts on the other. The specific pairing of these bases gives DNA its iconic double helix shape.
4. WHERE DO CELLS GET THE NUCLEOTIDE BUILDING BLOCKS TO MAKE DNA?
Cells obtain nucleotide building blocks from the food we consume. The DNA in food, like in vegetables and fish, breaks down into the necessary nucleotides. Moreover, our cells can synthesize these nucleotides from the beginning using atoms from the proteins, sugars, and fats we eat.