The Most Beautiful Notion in Biology
Now we’ve all at least heard or used the word DNA at least once in our lifetime. The word DNA and gene have become increasingly popular by being ascribed to our entire well-being and way of life. But what exactly does DNA do in our cells? Surely DNA doesn’t dictate most of our entire lives, including of our offspring’s, by just sitting around our cells doing nothing right? In order to understand the role DNA plays, we have to understand the Central Dogma of Molecular Biology.
DNA (short for deoxyribonucleic acid) consists of two strands of molecule, interlocking with each other in a double-helical winding structure. The information that is encoded in the DNA is the entire genetic makeup of you, your ancestors and your future children. The function of DNA resonates all throughout life in every living organism on Earth – it simply just contains the genetic information that are used for the growth, development and maintenance of all living things. Every DNA molecule is made up of a string of nucleotides (essentially the building blocks of nucleic acids). There are 4 different nucleotides that make up DNA, let’s just call them A, T, G and C for simplicity.
Just to give you an idea of how dense DNA really is, in every DNA molecule there is 3.2 billion of these nucleotides stacked on top of one another! If you were to put all your DNA molecules in your body end to end, the DNA would reach the Sun from the Earth, not once, not twice, but 600 times over! Now, we all know that every piece of information about an individual living thing can be found in its DNA. But if DNA is just a repeating sequence of nucleotides, how exactly does it convey a message? In comes the next sequence of the Central Dogma.
RNA (short for ribonucleic acid) are the cousins of DNA. However, there are a few key differences to tell them apart – unlike DNA, RNA only exists as a single strand and instead of having the nucleotide T, RNAs have its complementary cousin, U. There is a whole family of RNA in a normal human cell, but our main focus here is the RNA known as the messenger (mRNA). The genetic information constrained in the DNA is useless, unless that message gets written in the form of mRNA. This process is known simply as transcription – where one DNA strand is used as a template in order to build the corresponding mRNA strand where genetic information is copied.
Imagine if you will, the head designer or carpenter in an IKEA store. The designer knows all there is to know about the assembly and construction of every piece of furniture you can possibly get from the store. But how will the designer ensure that his/her customers know the steps required to construct the furniture? Hence, for every piece of furniture, the designer would simply write down all the necessary instructions on how to build the furniture in a comprehensive manual. The IKEA designer with his/her vast knowledge is the DNA. The instruction manual, the RNA.
These are not the typical proteins that you here about in the gym or in health fitness store. The proteins that I am talking about are biological molecules that have specific functions within a cell. Proteins are essentially the workhorses in a cell. They do virtually every process within a cell and are what that keep a cell functional, without them, nothing and absolutely nothing can happen. The building blocks of proteins are called amino acids. There are 20 different types of amino acids across all living organisms. The message in the mRNA that was transcribed from the DNA is what that is needed to build a protein. This process is known as translation – where every three nucleotides on the mRNA codes for a particular amino acid. Cellular factories known as ribosomes facilitates the translation of the mRNA message into the proteins.
Going back to our IKEA designer example from before. We have DNA in the designer and the RNA in the instruction manual, so what should the proteins be? Ultimately, the proteins are the finished IKEA furniture. The customers (ribosomes) purchase a product from the store and are given the instruction manual (RNA) and pieces of the furniture (amino acids). The customers would assemble the furniture based on the manual and the finished product is the protein which, hopefully, is functional and goes on to serve its purpose!
A simplistic diagrammatic view of the Central Dogma of Molecular Biology. Image courtesy of https://www.khanacademy.org/science/biology/gene-expression-central-dogma/central-dogma-transcription/a/intro-to-gene-expression-central-dogma
The flow of genetic information in a biological system – from DNA, to RNA to proteins – is known as the Central Dogma of Molecular Biology. This is perhaps the most revolutionary concept to have ever been introduced in Biology. Francis Crick, the co-discoverer of the structure of DNA, said this in 1958, “The Central Dogma. This states that once ‘information’ has passed into protein it cannot get out again. In more detail, the transfer of information from nucleic acid to nucleic acid, or from nucleic acid to protein may be possible, but transfer from protein to protein, or from protein to nucleic acid is impossible. Information means here the precise determination of sequence, either of bases in the nucleic acid or of amino acid residues in the protein”. Written simply, the Central Dogma states that DNA makes RNA and RNA makes proteins.