What I am going to tell you about RNA is very, very simplified, but I think it will give you the gist.
RNA or ribonucleic acid is much the same as DNA, a chain of nucleotides, but the sugar is always ribose (not deoxyribose), uracil replaces thymine, and RNA is usually single-stranded. RNA is essential in coding, decoding, regulation and expression of the genes coded in the DNA.
Structure DNA and RNA molecule – Copyright: Designua, Image ID: 124474282 via Shutterstock
There are several types of RNA: mRNA, rRNA, tRNA, and non-coding RNA.
1. mRNA – Messenger RNA: Encodes amino acid sequence of a polypeptide. mRNA synthesis involves separation of the DNA strands and synthesis of an RNA molecule with the action of an enzyme called RNA polymerase. One of the separated DNA strands is a template.
mRNA carries the genetic code copied from the DNA in the form of triplets of nucleotides called codons. Each codon specifies a particular amino acid, but one amino acid can be coded by many different codons or groups of three nucleotides.
There is some processing of mRNA before it moves from the nucleus to the cytoplasm of a cell.
2. rRNA – Ribosomal RNA. When combined with ribosomal proteins, rRNA makes a structure called a ribosome. The ribosome is the organelle where the mRNA is trranslated.
rRNA constitutes the predominant material within the ribosome, which is approximately 60% rRNA and 40% protein. Ribosomes contain two major rRNA subunits – the large A acts as an enzyme, catalyzing the bond formation between the amino acids. rRNA sequences are of ancient origin and are found in all known forms of life.
This is a three dimensional reconstruction of a ribosome, where blue is the small subunit and red is the large.
3. tRNA – Transfer RNA is the physical link between the mRNA and the amino acids that go into a protein. It does this by carrying an amino acid to a ribosome, as directed by a three-nucleotide sequence or codon in the mRNA. As such, tRNAs are a necessary component of translation, the biological synthesis of a protein originally coded in the DNA.
4. Non-coding RNA (ncRNA) is a functional RNA molecule that is transcribed from DNA but not translated into proteins. In general, ncRNAs function to regulate gene expression at the transcriptional (DNA to RNA) and post-transcriptional (RNA to protein) levels, and there are a lot of them, more being discovered all the time!
Hopefully you didn’t find this too confusing. I use to teach a more detailed version of this to my non-biology majors, because they would be living in a world where they will be confronted with these terms.