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Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are perhaps the most important molecules in cell biology, responsible for the storage and reading of genetic information that underpins all life. They are both linear polymers, consisting of sugars, phosphates and bases, but there are some key differences which separate the two1. These distinctions enable the two molecules to work together and fulfil their essential roles. Here, we look at 5 key differences between DNA and RNA. Before we delve into the differences, we take a look at these two nucleic acids side-by-side. A comparison of the helix and base structure of RNA and DNA DNA vs. RNA – A comparison chart
What are the key differences between DNA and RNA?We can identify five key categories where DNA and RNA differ:
FunctionDNA encodes all genetic information, and is the blueprint from which all biological life is created. And that’s only in the short-term. In the long-term, DNA is a storage device, a biological flash drive that allows the blueprint of life to be passed between generations2. RNA functions as the reader that decodes this flash drive. This reading process is multi-step and there are specialized RNAs for each of these steps. Below, we look in more detail at the three most important types of RNA. What are the three types of RNA?
SugarBoth DNA and RNA are built with a sugar backbone, but whereas the sugar in DNA is called deoxyribose (left in image), the sugar in RNA is called simply ribose (right in image). The ‘deoxy’ prefix denotes that, whilst RNA has two hydroxyl (-OH) groups attached to its carbon backbone, DNA has only one, and has a lone hydrogen atom attached instead. RNA’s extra hydroxyl group proves useful in the process of converting genetic code into mRNAs that can be made into proteins, whilst the deoxyribose sugar gives DNA more stability3. The chemical structures of deoxyribose (left) and ribose (right) sugars BasesThe nitrogen bases in DNA are the basic units of genetic code, and their correct ordering and pairing is essential to biological function. The four bases that make up this code are adenine (A), thymine (T), guanine (G) and cytosine (C). Bases pair off together in a double helix structure, these pairs being A and T, and C and G. RNA doesn’t contain thymine bases, replacing them with uracil bases (U), which pair to adenine1. StructureWhile the ubiquity of Francis Crick and James Watson’s (or should that be Rosalind Franklin’s?) DNA double helix means that the two-stranded structure of DNA structure is common knowledge, RNA’s single stranded format is not as well known. RNA can form into double-stranded structures, such as during translation, when mRNA and tRNA molecules pair. DNA polymers are also much longer than RNA polymers; the 2.3m long human genome consists of 46 chromosomes, each of which is a single, long DNA molecule. RNA molecules, by comparison, are much shorter3. LocationEukaryotic cells, including all animal and plant cells, house the great majority of their DNA in the nucleus, where it exists in a tightly compressed form, called a chromosome4. This squeezed format means the DNA can be easily stored and transferred. In addition to nuclear DNA, some DNA is present in energy-producing mitochondria, small organelles found free-floating in the cytoplasm, the area of the cell outside the nucleus. The three types of RNA are found in different locations. mRNA is made in the nucleus, with each mRNA fragment copied from its relative piece of DNA, before leaving the nucleus and entering the cytoplasm. The fragments are then shuttled around the cell as needed, moved along by the cell’s internal transport system, the cytoskeleton. tRNA, like mRNA, is a free-roaming molecule that moves around the cytoplasm. If it receives the correct signal from the ribosome, it will then hunt down amino acid subunits in the cytoplasm and bring them to the ribosome to be built into proteins5. rRNA, as previously mentioned, is found as part of ribosomes. Ribosomes are formed in an area of the nucleus called the nucleolus, before being exported to the cytoplasm, where some ribosomes float freely. Other cytoplasmic ribosomes are bound to the endoplasmic reticulum, a membranous structure that helps process proteins and export them from the cell5. Unusual types of DNA and RNAThe structure we have described in this article is certainly the most common form of DNA, but it isn’t the
whole story. Other forms of both DNA and RNA exist that subvert the classical structures of these nucleic acids. Z-DNA
A-DNA
Triplex DNA
Triplex-forming oligonucleotides (TFOs) can
bind conventional two-stranded DNA, which can help guide agents that are used to modify DNA to specific genomic locations. H-DNA is an endogenous, triple-stranded DNA molecule that encourages mutation of the
genome. dsRNA
References
Which of the following best describe the arrangement of genetic information in a DNA molecule?Which of the following best describes the arrangement of genetic information in a DNA molecule? The three-nucleotide words of a gene are arranged in a nonoverlapping series on the DNA template strand.
How is genetic information stored in the DNA molecule?DNA stores biological information in sequences of four bases of nucleic acid — adenine (A), thymine (T), cytosine (C) and guanine (G) — which are strung along ribbons of sugar- phosphate molecules in the shape of a double helix.
What is the structure of a DNA molecule?DNA is made of two linked strands that wind around each other to resemble a twisted ladder — a shape known as a double helix. Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups. Attached to each sugar is one of four bases: adenine (A), cytosine (C), guanine (G) or thymine (T).
Which molecular model best describes the structure of the DNA molecule?Double helix, as related to genomics, is a term used to describe the physical structure of DNA. A DNA molecule is made up of two linked strands that wind around each other to resemble a twisted ladder in a helix-like shape.
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