DNA Terminology
Understanding the Language that Chemically Describes DNA
Genes use a specific chemical language to store information. There is also a structural language that, if you understand it, will help you better understand DNA.
Watson and Crick. When James Watson and Francis Crick solved the puzzle that was the molecular structure of deoxyribonucleic acid or DNA, they won the Nobel Prize, and it was a one page publication. Now that is an impact. What they also did was provide us with a new language for describing DNA. Understanding the language of DNA chemistry makes comprehending many things about DNA vastly easier.
The Basic Components of DNA. Most everyone knows from the work of Watson and Crick thatthe DNA in our cells is maintained as a double helix, with two strands wrapped around each other, not unlike the supports on a spiral staircase. In DNA these supports, or backbone, consist of a long, linear polymer of alternating sugars and phosphates. The sugar is known as 2-deoxyribose and each of them has an attached phosphate group. Running along the polymer sugar-phosphate backbone between these supports, the stair treads if you will, are the nitrogen-containing bases. They make up the letters of DNA, A for adenine, C for cytosine, G for guanine, and T for thymine.
DNA has Complementarity. Determining the structure of DNA required that Watson and Crick pay careful attention to information that already had been uncovered by other scientists. One crucial piece of information came from the studies of Erwin Chargaff. He had shown that in all DNA samples analyzed the amount of adenine always equaled the amount of thymine and the amount of guanine always equaled the amount of cytosine (A = T and G = C). Watson and Crick used “Chargaff’s rules” to come up with the critical concept of two strands of DNA with complementary pairing of the nitrogen-containing bases. If one strand had an A then it was paired across from a T on the opposite strand. Likewise if one strand had a G then it was paired with a C on the other.
How to Replicate DNA. What complementary bases provided for Watson and Crick was the key insight into how DNA could be copied, or replicated. The bases on either strand could be used to identify and order the complementary bases on the other by “base-pairing”. If you unzip the double helix, each strand could serve as a template for the complementary strand to be synthesized. This would allow for the generation of two identical copies of the original double stranded DNA. This process, semi-conservative DNA replication, made it simple to postulate how genetic information could be accurately copied and passed on from a dividing cell to its two daughter cells.
Put It Together. The genetic information resides in the cell in the form of DNA. This double helical molecule consists of two sugar-phosphate backbones, each with a specific order of nitrogenous bases coming off of them. The rules of base-pairing allow us to predict the sequence of bases for both strands even if we only know the order on one. Complementary bases allow for the accurate semi-conservative replication of both strands when a cell divides to generate two new progeny.
