Every strand of RNA is a sequence of four building blocks called nucleotides. Each RNA nucleotide consists of three parts: a sugar, a phosphate group, and a nitrogen-containing base.
A folded strand of RNA, with its sugar and phosphate backbone shown in blue and its bases shown in green. (Image courtesy of Vossman, Wikimedia Commons)
The four RNA bases are adenine, uracil, guanine, and cytosine—often referred to as A, U, G, and C. RNA shares three bases in common with DNA: adenine, guanine, and cytosine. Instead of uracil, DNA contains thymine.
The sugar and phosphate groups form the backbone of a strand of RNA, and the bases bond to each other. RNA nucleotides contain a sugar called ribose, whereas DNA nucleotides contain a sugar called deoxyribose. This is spelled out in the full names of RNA and DNA: ribonucleic acid and deoxyribonucleic acid.
The four RNA bases bond together in complementary pairs. Different bases form bonds of different strengths. Guanine-Cytosine form the strongest bond, Adenine-Uracil form the next strongest bond, and Uracil-Guanine form the weakest bond.
Comparing RNA and DNA
DNA and RNA are both strings of chemical building blocks called nucleotides. And these nucleotides spell out a genetic code. That’s about where the similarities end though; these two molecules carry out very different functions in living things.
RNA is single stranded while DNA is double stranded.
DNA is double stranded, forms a double helix (the two strands spiral around each other) is stable and stays in the nucleus. RNA is single stranded (except in rare cases), can fold into complex 3D shapes, is relatively unstable and can leave the nucleus.
DNA stores information as genes. Genes contain the blueprints for RNAs and proteins. Many "non-coding" RNAs act as molecular machines. They carry out various functions that keep us alive. Some of their functions include facilitating cellular processes, protecting the cell from invading viruses, and altering other biomolecules.
Messenger RNA (mRNA)
The mRNA code is translated to make a protein by a ribosome, using amino acids carried by tRNAs.
Messenger RNAs (mRNAs) are messengers between DNA and a cell’s protein-assembly machines (ribosomes). They carry coded instructions for building proteins.
Unlike most of the VirtuaLab RNAs, mRNAs do not usually fold into 3D shapes (and when they do, they have to be unfolded in order to be read by a ribosome). Instead, they resemble long twisted strings.
mRNAs form from a DNA template in a process called transcription. When an mRNA is made, it often needs to be edited before it can be translated into a protein. This is carried out by a spliceosome, a molecular machine made of RNAs and proteins, which splices out unwanted RNA from newly made mRNA.
Translating the mRNA code
The four nucleotides, A, U, C, and G, are the basis of the code in mRNA. Every set of three nucleotides corresponds to a specific amino acid (amino acids are the building blocks of proteins). For example, the code UAC, CGA, GGA on mRNA means “tyrosine, arginine, glycine.” Every three nucleotides of mRNA are recognized by a particular transfer RNA (tRNA) that carries a particular amino acid. Amino acids from tRNAs are linked together to make a protein in a cell’s protein-assembly machine (ribosome) in the order specified in an mRNA.