DNA, also known as Deoxyribonucleic acid is the blueprint of life – meaning it stores all information that makes up any living organism. But, how does DNA store genetic information?
James Watson and Francis Crick discovered the structure of DNA – two (polynucleotide) strands intertwined in a double helix –in the year 1953. They found that DNA stores information using a simple four-letter code, which involves a cool feature known as complementary base pairing.
So how does complementary base pairing work?
We all have learned that DNA has two strands twisted around each other to form double helix, which kind of would resemble a ladder if we flatten it out.
In DNA, each step in the ladder is made of two pieces, and these two pieces are called bases. DNA has four bases named – adenine, cytosine, guanine and thymine. They are abbreviated simply by their first initials, that is – A,C, G and T – and these letters represent the code DNA uses to store genetic information.
One key part of Watson and Crick’s discovery was the way in which these bases pair up with one another. They found that A pairs only with T, and C pairs only with G. That is – A and T complement one another and C in G complement one another. This also means that C and G cannot pair with A or T.
For example, if one strand of DNA has bases CTGAC, the other will have GACTG. One way to remember which bases pair with which is to write the letters in alphabetical order, then below that – write the letters in the reverse order.
But, what does all this mean for a cell?
When a cell prepares for cell division, it makes a replica of its DNA so that the two resulting daughter cells have exactly the same genetic information, or DNA, as the parent cell. So complementary base pairing means that cells can replicate their DNA quickly and efficiently.
During the replication process, the double helix separates down the middle where the pairs of bases join. This exposes the sequences of A’s C’s G’s and T’s on each side. Then, groups of enzymes come along and add complementary bases one after another along the entire length of both DNA strands, that is – gene after gene along the entire length of the chromosome. Then in the end, there are two identical chromosomes that are encoded with the same genetic information.
Complementary base pairing also plays an important role when cells make proteins. During protein synthesis, the DNA that is the gene that codes for the needed protein – opens up, which exposes the sequences of bases in that gene. The sequence of bases is then copied in the form of RNA, but with one important difference – RNA has no T (thymine). Instead of the base thymine, it uses a base called uracil (abbreviated as U). So, when a gene is copied during protein synthesis, every A in the DNA is matched with a U in the RNA.
You can read more about how the cell converts DNA into working proteins at – Translation: DNA to mRNA to Protein (Nature Education)
Complementary base pairing has helped scientists in understanding how cancer happens. For example, if they know the sequence of bases for a piece of DNA from a cell, they can learn what the base sequence is for the opposite piece by using complementary base pairing.
Gene sequencing technology reveals the lineup of bases in DNA and a messenger RNA. Scientists can then use complementary base pairing to identify the gene that produced that messenger RNA. Once scientists know the sequence of amino acids in a protein, they can decipher the sequence of bases in the messenger RNA for the protein and then the gene that codes for that protein.
Complementary base pairing also allows scientists to compare genes from cancer cells and healthy cells from a patient. This helps them learn more about why cancer happens and how tumors grow.
Watson and Crick’s discovery has been called the most important biological work of all time. It also earned them the Nobel Prize for Physiology or Medicine in 1962.
Further Readings and References:
- An Introduction to Molecular Biology/DNA the unit of life (WikiBooks)
- Introduction To Genetics: The Molecular Basis Of Life ‘DNA’
- DNA Damage & Repair: Mechanisms for Maintaining DNA Integrity (Nature)
- DNA – The Blueprint of Life