Rna Function
Ribonucleic acid (RNA) is a nucleic acid that is similar, but not identical, to a single strand of deoxyribonucleic acid (DNA). In RNA, the base uracil is substituted for the base thymine in the genetic code. While DNA and RNA are very similar in their composition, RNA has a much more versatile role. It both conveys genetic information and catalyzes reactions.
There are five major types of RNA that are found in eukaryotic cells. The types are known as heterogeneous nuclear RNA (hnRNA), messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA), and small nuclear RNA. Depending on the type of RNA, it can function as a carrier for genetic information, a catalyst for biochemical reactions, an adapter molecule in protein synthesis, and a structural molecule in cell organelles.
RNA functions principally to convey the genetic information contained in DNA into the gene product, a protein. In the nucleus, a series of enzymatic reactions produces hnRNA from DNA. Enzymes are molecules that help (facilitate) a reaction but that are not altered by the reaction. Accordingly, they are not a part of the final product of a reaction. This RNA species is a direct copy of DNA, and so contains the coding and noncoding regions of the parent molecule. The extraneous noncoding regions are spliced out as the hnRNA is converted to mRNA. The mRNA is directed to the cytoplasm, in this way, it functions as the carrier for information from the DNA to the ribosomes, the cell's protein synthesizing organelles.
The ribosomes interact with the mRNA and construct a protein based on the instructions in the nucleotide sequence. A component of the ribosome is rRNA. It provides the structure and shape for the catalytic areas of the ribosome, and acts as a catalyst (or a ribozyme) for the action of another ribosomal RNA, the tRNA. Protein synthesis is contingent upon tRNA. It is the functional bridge between the coding nucleotides on the mRNA and the amino acids used to construct the protein. During protein synthesis, one end of the tRNA interacts with three nucleotides on the mRNA. The other end of the tRNA carries an amino acid. The amino acid is transferred and bonded to the growing chain of amino acids that have resulted from the action of other tRNA species.
Another form of RNA that acts as a ribozyme is snRNA. During splicing of the hnRNA, snRNA catalyzes reactions in the spliceosome, a group of biomolecules that accomplish the splicing.
RNA is the sole genetic material present in viruses known as single strand RNA viruses. One class, the Retroviridae, contains an enzyme called reverse transcriptase that uses the RNA as a template for the synthesis of viral DNA. The viral DNA integrates into the host cell genome to provide the template for viral RNA synthesis by host-derived mechanisms. Retroviruses are also noteworthy because the group includes viruses associated with leukemia and human immunodeficiencies.
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