Messenger ribonucleic acid
Ribonucleic acid (RNA) is a nucleic acid marked by being generally single-stranded, and composed of repeating nucleotide units of ribose sugar, phosphate group, and nitrogenous base. One of the main functions of RNA is for protein synthesis. There are three major types of RNA involved in this process: (1) messenger RNA, (2) transfer RNA, and (3) ribosomal RNA.
The messenger ribonucleic acid or mRNA is a type of RNA that during protein synthesis carries the code for a specific protein. Protein synthesis is comprised of two processes: the transcription and the translation. It is during the transcription that the mRNA is synthesized from the DNA template. After the mRNA is produced, it will proceed to the next phase of protein synthesis: translation. Translation is the process where amino acids will be joined together in a particular order as specified by the genetic code. It occurs in the cytoplasm and involves the ribosomes. Translation is comprised of the following steps: activation, initiation, elongation, and termination.
In eukaryotes, the mRNA is produced in the nucleus (during transcription). This mRNA needs to be processed extensively to become mature. This extensive processing includes the addition of a 5' cap at the 5' end and a sequence of adenylate groups at the 3' end, the poly a tail, as well as the removal of any introns and the splicing together of exons. When the pre-mRNA has been completely processed, it is now called a mature mRNA, which will then be transported for translation into the site of protein synthesis (ribosome) in the cytoplasm through the nuclear pore. The eukaryotic mRNA has relatively longer lifespan, e.g. mammalian mRNA can live from several minutes to days.
In prokaryotes such as bacteria, the mRNA is produced and translated in the cytoplasm of the bacterial cell. The prokaryotic mRNA is produced by splicing a large primary transcript from a DNA sequence. The mRNAs of prokaryotes are usually very short lived (from seconds to more than an hour) and protein synthesis starts even while the mRNA is still being synthesized. The resulting mRNA is essentially mature upon transcription and requires no extensive processing.
- messenger RNA