Question: What do DNA and RNA have in common?
About the article "Biomolecule", section "Nucleosides and nucleotides".

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1930–1950.RNA and DNA have distinct chemical properties.
When first studied in the early 1900s, the chemical and biological differences between RNA and DNA were not apparent, and they were named after the materials from which they were isolated; RNA was initially known as "yeast nucleic acid" and DNA was "pancreas nucleic acid".
Using diagnostic chemical tests, carbohydrate chemists showed that the two nucleic acids contained different sugars, whereupon the common name for RNA became "ribose nucleic acid".
Other early biochemical studies showed that RNA was readily broken down at high pH, while DNA was stable (although denatured) in alkali.
Nucleoside composition analysis showed first that RNA contained similar nucleobases to DNA, with uracil instead of thymine, and that RNA contained a number of minor nucleobase components, e.g.
small amounts of pseudouridine and dimethylguanine. 
The discovery of catalytic RNA (ribozymes) showed that RNA could both encode genetic information (like DNA) and catalyze specific biochemical reactions (like protein enzymes).
This realization led to the RNA World Hypothesis, a proposal that RNA may have played a critical role in prebiotic evolution at a time before the molecules with more specialized functions (DNA and proteins) came to dominate biological information coding and catalysis.
Although it is not possible for us to know the course of prebiotic evolution with any certainty, the presence of functional RNA molecules with common ancestry in all modern-day life forms is a strong argument that RNA was widely present at the time of the last common ancestor. 
The chemical properties of RNA make large RNA molecules inherently fragile, and they can easily be broken down into their constituent nucleotides through hydrolysis.
These limitations do not make use of RNA as an information storage system impossible, simply energy intensive (to repair or replace damaged RNA molecules) and prone to mutation.
While this makes it unsuitable for current 'DNA optimised' life, it may have been acceptable for more primitive life. 
Physical definitions.RNA genes and genomes in the world.
When proteins are manufactured, the gene is first copied into RNA as an intermediate product.
In other cases, the RNA molecules are the actual functional products.
For example, RNAs known as ribozymes are capable of enzymatic function, and microRNA has a regulatory role.
The DNA sequences from which such RNAs are transcribed are known as RNA genes.
Some viruses store their entire genomes in the form of RNA, and contain no DNA at all.
Because they use RNA to store genes, their cellular hosts may synthesize their proteins as soon as they are infected and without the delay in waiting for transcription.
On the other hand, RNA retroviruses, such as HIV, require the reverse transcription of their genome from RNA into DNA before their proteins can be synthesized.
In 2006, French researchers came across a puzzling example of RNA-mediated inheritance in mice.
Mice with a loss-of-function mutation in the gene Kit have white tails.
Offspring of these mutants can have white tails despite having only normal Kit genes.
The research team traced this effect back to mutated Kit RNA.
While RNA is common as genetic storage material in viruses, in mammals in particular RNA inheritance has been observed very rarely. 
Studies of retroviruses led to the first demonstrated synthesis of DNA from RNA templates, a fundamental mode for transferring genetic material that occurs in both eukaryotes and prokaryotes.
It has been speculated that the RNA to DNA transcription processes used by retroviruses may have first caused DNA to be used as genetic material.
In this model, the RNA world hypothesis, cellular organisms adopted the more chemically stable DNA when retroviruses evolved to create DNA from the RNA templates.