DNA, or deoxyribonucleic acid, is like a blueprint of biological guidelines that a living organism must follow to exist and remain functional. RNA, or ribonucleic acid, helps carry out this blueprint’s guidelines. Of the two, RNA is more versatile than DNA, capable of performing numerous, diverse tasks in an organism, but DNA is more stable and holds more complex information for longer periods of time.
DNA is found in the nucleus of a cell (nuclear DNA) and in mitochondria (mitochondrial DNA). It has two nucleotide strands which consist of its phosphate group, five-carbon sugar (the stable 2-deoxyribose), and four nitrogen-containing nucleobases: adenine, thymine, cytosine, and guanine.
During transcription, RNA, a single-stranded, linear molecule, is formed. It is complementary to DNA, helping to carry out the tasks that DNA lists for it to do. Like DNA, RNA is composed of its phosphate group, five-carbon sugar (the less stable ribose), and four nitrogen-containing nucleobases: adenine, uracil (not thymine), guanine, and cytosine.
In both molecules, the nucleobases are attached to their sugar-phosphate backbone. Each nucleobase on a nucleotide strand of DNA attaches to its partner nucleobase on a second strand: adenine links to thymine, and cytosine links to guanine. This linking causes DNA’s two strands to twist and wind around each other, forming a variety of shapes, such as the famous double helix (DNA’s “relaxed” form),circles, and supercoils.
DNA provides living organisms with guidelines—genetic information in chromosomal DNA—that help determine the nature of an organism’s biology, how it will look and function, based on information passed down from former generations through reproduction. The slow, steady changes found in DNA over time, known as mutations, which can be destructive, neutral, or beneficial to an organism, are at the core of the theory of evolution.
Genes are found in small segments of long DNA strands; humans have around 19,000 genes. The detailed instructions found in genes—determined by how nucleobases in DNA are ordered—are responsible for both the big and small differences between different living organisms and even among similar living organisms. The genetic information in DNA is what makes plants look like plants, dogs look like dogs, andhumans look like humans; it is also what prevents different species from producing offspring (their DNA will not match up to form new, healthy life). Genetic DNA is what causes some people to have curly, black hair and others to have straight, blond hair, and what makes identical twins look so similar. (See also Genotype vs Phenotype.)
RNA has several different functions that, though all interconnected, vary slightly depending on the type. There are three main types of RNA:
- Messenger RNA (mRNA)transcribes genetic information from the DNA found in a cell’s nucleus, and then carries this information to the cell’s cytoplasm and ribosome.
- Transfer RNA (tRNA)is found in a cell’s cytoplasm and is closely related to mRNA as its helper. tRNA literally transfers amino acids, the core components of proteins, to the mRNA in a ribosome.
- Ribosomal RNA (rRNA)is found in a cell’s cytoplasm. In the ribosome, it takes mRNA and tRNA and translates the information they provide. From this information, it “learns” whether it should create, or synthesize, a polypeptide or protein.
DNA’s genes are expressed, or manifested, through the proteins that its nucleotides produce with the help of RNA. Traits (phenotypes) come from which proteins are made and which are switched on or off. The information found in DNA determines which traits are to be created, activated, or deactivated, while the various forms of RNA do the work.
One hypothesis suggests that RNA existed before DNA and that DNA was a mutation of RNA. The video below discusses this hypothesis in greater depth.
Movie- The RNA Origin of Life
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