RNA

RNA (ribonucleic acid) is a biological macromolecule that stores and processes genetic information, catalyzes chemical reactions and regulates biological processes. Just like the other nucleic acid (DNA), it is a linear polymer (a "strand") of nucleotide building blocks. These building blocks themselves are made up of a sugar linked to a (nitrogenous) base and a phosphate. RNA utilizes a different set of bases than DNA, and it sugar (ribose) contains one additional hydroxyl group compared to that of DNA (deoxyribose). Different than DNA, which mostly occurs in pairs of complementary strands in its biological context, RNA mostly lacks a complementary strand, leading to a larger variety of 3D structures and biological functions.

RNA structure and function

spinqualitylabelsall models Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D This is a tour of different biological processes, showcasing the role of RNA. In current biology, RNA interacts with DNA and proteins to support life. The "RNA world" hypothesis states that early on in the evolution of life, DNA and proteins did not yet exist and RNA had DNA-like (genetic storage) and protein-like (metabolism, biosynthesis, etc) roles. Genetic information RNA plays key roles in gene expression, in the form of mRNA (messenger RNA), tRNA (transfer RNA) and rRNA (ribosomal RNA), the classic three types of RNA. Beyond these roles, RNA also serves to store genetic information and to regulate and modulate it. Storage All known organisms use DNA as the storage molecule for genetic information. Some viruses, however use RNA instead. They are classified into double-stranded RNA viruses and plus or minus single-stranded RNA viruses depending on how they use RNA to store genetic information. For example, human immunodeficiency virus carries genetic information in the form of single stranded RNA. In the figure, the RNA is located in the dark rectangular blob inside the circular virus particles. Transcription RNA is synthesized by RNA polymerases using DNA (or sometimes RNA) as a template. During synthesis, the template and the newly synthesized RNA form a base-paired, anti-parallel structure. Shown here is the initiation of transcription by phage T7 RNA polymerase () Post-transcriptional modification Introns are segments of RNA that have catalytic activity. These elements can splice RNA (remove the intron) and sometimes act as retrotransposons (i.e. they can insert themselves into pieces of RNA, which then - via reverse transcription - changes the sequence of DNA). The class IIc intron shown here in complex with a small piece of its substrate (the exon) catalyzes phophodiester transesterification using bound magnesium ions. Translation Ribosomes synthesize proteins with sequences determined by mRNA. The ribosome is a complex of rRNA and protein. Shown here is a small part of the ribosome illustrating protein-RNA interactions: ribosomal RNA (). When synthesizing proteins, ribosomes follow the genetic code to translate an RNA sequence (grouped into codons of 3 nucleotides) into a protein sequence.tRNAs are the adapter molecules that embody the genetic code. Each tRNA is covalently bound to a specific amino acid at one end and display an anti-codon on the other end (for more details, see transfer RNA) Catalysis In addition to the examples of catalytic RNA already mentioned in the previous section (ribosome, introns), other ribozymes exist. Hammerhead RNA Hammerhead ribozyme () RNAse P RNAse P modifies folded tRNA. Regulation Only a small fraction of the human genome codes for proteins, tRNA or rRNA. The remainder has been called "junk DNA" in the past, but some of it codes for RNA that plays a role in gene regulation. Riboswitches Riboswitches work by binding to segments of RNA, thereby changing the structure of it (for example, by competing with an interaction supporting one structure, they allow it to fold into a different structure. The structure of the riboswitches is sometimes dependent on binding to small molecules, like the riboswitch bound to S-adenosylmethionine shown here. RNA silencing siRNA ()

Chemistry

1. Base: flat, aromatic, hydrogen-bonding capability, base modifications, base pairing, transfer RNA
2. Sugar phosphate backbone: torsion angles, sugar pucker, phosphate-phosphate distance

Transcription and Translation

The expression of genes into proteins and is a process involving two stages called transcription and translation. In the transcription stage a strand of DNA molecule serves as a template for the synthesis of an RNA molecule called messenger RNA. In the case of RNAs that code for polypetides, this messenger RNA is then translated into proteins on ribosomes.

Post-transcriptionally, specific nucleotides in RNA are often further modified. This is most frequent in [tRNA|transfer ribonucleic acid (tRNAs)]], the adapter molecules of Translation, and ribosomal ribonucleic acids (rRNAs) of the ribosome.

See Also

• Ribosome
• Translation
• DNA Replication, Transcription and Translation
• Transfer ribonucleic acid (tRNA)
• Ribozyme
• Kink-turn motif
• Pseudouridine
• Non-Standard Residues
• DNA
• For additional information, see: Nucleic Acids

External Resources

• HD-RNAS: Hierarchical Database of RNA Structures is a systematic hierarchical organization classifying all RNAs available in the Protein Data Bank. This helps make it easier to navigate the availble structural data given the large numbers of redundant files and ambiguous synthetic sequences.
• Liley Database

Proteopedia Page Contributors and Editors (what is this?)

Karsten Theis, Wayne Decatur, Michal Harel