A biologically important molecule, ribonucleic acid (RNA) is similar in some respects to deoxyribonucleic acid (DNA) but has some important structural and functional differences. There are several types of ribonucleic acid, each of which plays a different role within the cell. Ribonucleic acids perform several essential tasks in protein synthesis and are involved in gene regulation.
RNA and DNA are both called nucleic acids and share a similar basic structure. Both types of nucleic acid are made up of units called nucleotides. Each nucleotide is composed of three molecules: a phosphate, a sugar and a nitrogenous base. There are several different nitrogenous bases, and it is the sequence of these molecules that allows DNA and RNA to store and transmit information about the long-term and day-to-day maintenance of the cell.
Although they share some similarities, ribonucleic acid and deoxyribonucleic acid molecules are different in three important ways. First, an RNA molecule is single-stranded, whereas DNA is a double-stranded molecule. Second, RNA contains a sugar called ribose, and DNA contains a sugar called deoxyribose. The third difference is that in DNA, the complementary base pair for adenine is thymine; whereas in RNA, the base pair for adenine is a modified version of thymine known as uracil.
There are three main types of ribonucleic acid. These are transfer RNA (tRNA), messenger RNA (mRNA) and ribosomal RNA (rRNA). These three molecules are structurally similar but perform very different functions.
Messenger RNA is the product of a process called transcription. In this process, the genetic code carried in a section of DNA is copied, resulting in the synthesis of a molecule of mRNA. The mRNA is an exact copy of a section of DNA that codes for a single protein. After it has been made, this mRNA travels from the cell's nucleus to the cytoplasm, where it undergoes a new cellular process with help from another type of ribonucleic acid.
In the cytoplasm of the cell, the mRNA comes into contact with transfer RNA molecules. Transfer RNA helps manufacture proteins by transporting amino acids to the site of protein synthesis. The tRNA uses mRNA molecules as a template for building the protein by “reading” the mRNA molecule to determine the order in which amino acids are placed in the protein chain. This process is called translation.
The third type of RNA, ribosomal RNA, is the site at which translation occurs. Ribosomal RNA molecules are the site at which mRNA is translated into proteins. Ribosomal RNA helps in this process by interacting with both messenger and transfer RNA molecules and by acting as a site of enzyme activity.
Other types of ribonucleic acid include micro RNA and double-stranded RNA. Micro RNA is used by cells to help regulate the transcription of messenger RNA, and can both increase or decrease the rate at which a particular gene is made into proteins. Double-stranded RNA, which is found in certain types of viruses, can enter cells and interfere with translation and transcription processes by acting in a manner similar to micro RNA.