Advancing Evolution:RNA
From Activating Evolution
RNA (Ribonucleic Acid) is a single-stranded nucleic acid polymer that is composed of nucleotide monomers. RNA serves as the template for translation of genes into proteins, transferring amino acids to the ribosome to form proteins, and also translating the transcript into proteins.
There are three basic differences between RNA and DNA. While RNA uses a sugar and a phosphate group as well as four nucleotide bases, the sugar used is ribose instead of deoxyribose. When synthesizing, the base thymine is replaced with Uracil. The major difference is that whereas DNA is double stranded, RNA is single stranded.
There are three types of RNA:
- Messenger RNA, or mRNA, is RNA that carries information from DNA to the ribosome sites of protein synthesis in the cell. Once mRNA has been transcribed from DNA, it is exported from the nucleus into the cytoplasm (in eukaryotes mRNA is "processed" before being exported), where it is bound to ribosomes and translated into its corresponding protein form with the help of tRNA. After a certain amount of time the message degrades into its component nucleotides, usually with the assistance of RNA polymerases.
- Transfer RNA, or tRNA, is a small RNA chain of about 74-95 nucleotides that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. It has sites for amino-acid attachment and an anticodon region for codon recognition that binds to a specific sequence on the messenger RNA chain through hydrogen bonding. It is a type of non-coding RNA.
- Ribosomal RNA, or rRNA is a component of the ribosomes, the protein synthetic factories in the cell. Eukaryotic ribosomes contain four different rRNA molecules: 18S, 5.8S, 28S, and 5S rRNA. Three of the rRNA molecules are synthesized in the nucleolus, and one is synthesized elsewhere. rRNA molecules are extremely abundant and make up at least 80% of the RNA molecules found in a typical eukaryotic cell.
In the cytoplasm, ribsomal RNA and protein combine to form a nucleoprotein called a ribosome. The ribosome binds mRNA and carries out protein synthesis. Several ribosomes may be attached to a single mRNA at any time.
[edit] References
"RNA." Wikipedia. 7 March 2007. <http://en.wikipedia.org/wiki/RNA>
Cambell and Reece. Biology, 7th ed. Pearson, 2005.
