RiboNucleic Acid (RNA) is the single stranded cousin of DeoxyriboNucleic Acid (DNA), the molecule of heredity which most people will be more familiar with. But RNA is also an important molecule in the normal functioning of a eukaryotic cell, like a human cell, and is also the genetic material that lies inside many viruses as well. RNA is particularly vital in the synthesis of proteins, the fundamental building blocks of cells.
The structure of the RNA molecule is a chain of nucleotides, each of which consists of a nitrogenous base (adenine, cytosine, guanine or uracil), a ribose sugar, and a phosphate. One difference between RNA and DNA is that RNA usually exists in a single stranded form unlike DNA which exists in the double stranded, double-helix shape, which was so famously discovered by Crick and Watson. Another main difference is that the ribose sugar found in RNA is replaced by a deoxyribose sugar in DNA. A third difference is in terms of the bases, with uracil being present in RNA as a replacement for thymine in DNA.
There are several different types of RNA. Messenger RNA is responsible for taking information from the DNA and delivering it to the ribosomes where polypeptide synthesis occurs. The ribosomes contain another type of RNA called ribosomal RNA which is capable of reading the messages of the messenger RNA and then translating that message into a form that allows the production of proteins. Transfer RNA are another type of RNA that provide amino acid to the ribosomes during protein synthesis. But there are other RNA as well with regulatory functions within the cell and these are called regulatory RNA.
RNA synthesis from DNA is done with the help of an enzyme called RNA polymerase in a process known as transcription. Here the enzyme binds to a sequence of DNA normally upstream of the relevant gene that is known as a promoter. The DNA is then unwound and the RNA molecule that is complementary to the DNA in the sequence. After transcription the RNA may then be modified by other enzymes.
RNA is capable of carrying genetic information and this is particularly important in the case of viruses. These infectious particles are loaded with genetic material inside their capsids and this can come in either DNA or RNA forms. The information contained therein is powerful enough to get the virus to a host cell, enter the host cell, splice themselves into the host genome and thereby hijack the machinery of the cell to get themselves replicated. So RNA should not be seen as some sort of inferior or incomplete version of DNA. It does many important things in its own right and even has replicatory possibilities.