What is the difference between DNA, mRNA and tRNA? and why are they different?

DNA, tRNA and mRNA are all essential macromolecular biological molecules involved in genetics and protein production. The two major categories of genetic molecules are DNA and RNA, with both tRNA and mRNA being different types of RNA. Whilst all three have similar structures, there are still major differences within both structure and function.

Components: DNA is the abbreviation of Deoxyribonucleic acid, which is a long polymer of DNA nucleotides. Within each DNA nucleotide, there is 1 deoxyribose sugar (a pentose sugar), 1 phosphate group and 1 base (from the options of Guanine, Cytosine, Thymine or Adenine). RNA on the other hand, is fully called Ribonucleic acid, which is a polymer of RNA nucleotides. Each RNA nucleotide consists of a ribose sugar (also pentose sugar), which differs from deoxyribose sugar by having an extra hydrogen atom within the sugar. It also contains a phosphate group, just like DNA and lastly, also contains a base but from the options of Guanine, Cytosine, Adenine and Uracil (instead of Thymine).

Structure: DNA exists as a double stranded structure with two strands running in anti-parallel directions. The two strands are held together by hydrogen bonds and twist together to form a double helix. A single molecule of DNA can also be very long. RNA on the other hand, are single stranded polymers that are much shorter. mRNA is a straight chain molecule, whereas tRNA folds back onto itself forming three hairpin loops, making the overall molecule a “three leaf clover” shape. Additionally, with DNA and tRNA, there are often additional amino acids/ proteins attached. DNA are wrapped around histones whereas tRNA has a specific amino acid attached.

Location: Whilst DNA is mostly found within the nucleus (with the exception of during mitosis or meiosis), both RNA molecules are found within the cytoplasm.

Function: DNA functions as a storage molecule for all the organism’s genetic information. It is used in the first step of protein synthesis (transcription) to create the messenger molecule mRNA. mRNA and tRNA on the other hand are required for the second stage of protein synthesis (translation), with mRNA acting as a “messenger” of the DNA. When the codon of a mRNA matches the anti-codon of a tRNA, a match is made and the corresponding amino acid on the tRNA is used for protein synthesis.

The major reasons for the differences between the structures of the three molecules are related to their function and recognition. Your cells need to be able to recognise between RNA and DNA in order to ensure both are used for respective purposes.

The different structures are also tailored for the specific purposes of each molecule. DNA’s double helix structure makes it highly stable and much more resistant to damage, which is important for a storage molecule. mRNA is highly accessible as a short single stranded structure, important as its purpose is not to last long, but to be used as an intermediate for translation. The double stranded nature of DNA is also important for the semi-conservative replication, ensuring daughter DNA produced are identical to the templates used.