Ribonucleic Acid, RNA, is typically found as a single stranded chain of ribonucleotides and is found in both prokaryotic and eukaryotic cells and can perform a variety of jobs in the cell. Certain types of RNA lead to the coding of a protein. Messenger RNA (mRNA), for example, transfers genetic information from the DNA to the ribosomes. But there is also non-coding RNA to be found in the biological world and it can play some pretty important roles. So what might it be doing?
One of the important examples of a type of non-coding RNA (ncRNA) is that of transfer RNA (tRNA). This form of RNA molecule, with only around 80 nucleotides, and shaped like a cloverleaf, is able to take the right amino acids to the ribosomes for the process of translation, where a new polypeptide chain is formed during the more general process of protein synthesis. The tRNA molecules are able to act as adaptors that match up particular amino acids to particular codons on the mRNA that is being processed.
Another important example is that of ribosomal RNA (rRNA). This form of the RNA molecule represents a significant proportion of the RNA found in cells and, together with proteins, forms the structure of the ribosomes, where the process of protein synthesis occurs in the cell. Ribosomal RNA is implicated in initiating the process of translation. In eukaryotic cells rRNA is transcribed from DNA in the nucleoli whereas in prokaryotic cells it comes from clustered ribosomal genes.
There are a variety of other types of non-coding RNA as well. So-called micro-RNAs (miRNA), for example, are tiny RNAs of around just 21-23 nucleotides, and are to be found in higher eukaryotic cells. These are implicated in the regulation of many thousands of genes. They are capable of modifying gene expression by binding to mRNA along partial sections to which they are complementary. Typically they down-regulate the expression of the gene.
Another type of note is the small nucleolar RNAs (snoRNAs), which can guide the modification of other RNAs, such as ribosomal RNAs, for example. Small interfering RNAs (siRNAs), meanwhile, are involved in interfering with the expression of a particular gene, whilst piwi-interacting RNAs (piRNAs) form complexes with piwi proteins and are implicated in gene silencing. Numerous examples of long ncRNAs (over 200 nucleotides) also exist with a variety of functions. It is also worth noting that damage to ncRNAs, through mutation or imbalance, for example, is implicated in diseases such as cancer, Prader-Willi syndrome, and Alzheimer’s disease.
