What is RNA and how is it different from DNA?
RNA is comprised of a long chain of nucleotides and is typically single stranded. There are a number of organisms that use RNA as their main genetic material and there are also multiple forms of RNA that are used to accomplish various tasks within organisms using DNA as their genetic material. RNA contains four base nucleotides: guanine, adenine, uracil, and cytosine. In organisms which use DNA as their genetic material, RNA is usually used for gene expression and silencing as well as helping to direct the synthesis of proteins.
DNA is usually double stranded and most multicellular organisms use DNA as their basic genetic material. DNA is typically composed of a very long strand of nucleotides which are bound up by proteins until expression is needed, at which time they are unbound and allowed to be processed and expressed. The four base nucleotides of DNA are adenine, guanine, cytosine, and thymine. DNA is most suited to the storage of massive amounts of genetic information and typically contains duplicate sequences in order to provide some form of redundancy to prevent loss of information. The two strands of DNA run anti-parallel to each other. DNA is typically highly bound into structures known as chromosomes which duplicate as part of cell division.
RNA differs from proteins in three fundamental ways. DNA is almost always double stranded whereas RNA is usually a single stranded molecule and is comprised of a much shorter chain of nucleotides than DNA. DNA contains deoxyribose in its sugar-phosphate backbone whereas RNA contains ribose. Ribose has a hydroxyl group present at the two prime position of the pentose ring and deoxyribose does not.
Finally, the base that is complementary to adenine is uracil instead of thymine. An unmethylated form of thymine is uracil. Most RNAs, when active, have sequences in their nucleotide chain that are self-complementary and allow the RNA to form various structures (including double helices, though not as long as those double helices that are formed by DNA.). DNA does not form the types of tertiary structures that RNA forms. The tertiary structures that are formed by RNA molecules more closely resemble those that proteins form in their active state.
Typically, RNA is not as highly bound up as DNA and can be accessed for translation at most anytime if it is located in the right area. Unlike DNA, there are multiple subtypes of RNA all of which play an important biological role. Messenger RNA is used to carry information about a specific protein sequence to ribosomes. Ribosomes then translate that protein sequence into the proteins themselves. Transfer RNA are used to carry the various amino acids to the ribosomes for assembly into the polypeptide sequences of the proteins being created. In addition to RNA molecules that are primarily used for protein synthesis, there are a number of other types.
Many viruses encode their entire genome on RNA molecules and then use the machinery of other cells in order to replicate their proteins and their RNA sequence. Regulatory RNA can be used to do a number of important things including the down-regulation of gene expression or the silencing of mRNA molecules which are carrying protein messages. This silencing occurs when a regulatory RNA binds to a complementary sequence on the mRNA and prevents it from being translated.
Written By: Alexander Maness, United States (M.S. in Biotechnology)
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Edited by: Rajesh Bihani ( Find me on Google+ )