RNA - Structure

Structure

Each nucleotide in RNA contains a ribose sugar, with carbons numbered 1' through 5'. A base is attached to the 1' position, in general, adenine (A), cytosine (C), guanine (G), or uracil (U). Adenine and guanine are purines, cytosine, and uracil are pyrimidines. A phosphate group is attached to the 3' position of one ribose and the 5' position of the next. The phosphate groups have a negative charge each at physiological pH, making RNA a charged molecule (polyanion). The bases may form hydrogen bonds between cytosine and guanine, between adenine and uracil and between guanine and uracil. However, other interactions are possible, such as a group of adenine bases binding to each other in a bulge, or the GNRA tetraloop that has a guanine–adenine base-pair.

An important structural feature of RNA that distinguishes it from DNA is the presence of a hydroxyl group at the 2' position of the ribose sugar. The presence of this functional group causes the helix to adopt the A-form geometry rather than the B-form most commonly observed in DNA. This results in a very deep and narrow major groove and a shallow and wide minor groove. A second consequence of the presence of the 2'-hydroxyl group is that in conformationally flexible regions of an RNA molecule (that is, not involved in formation of a double helix), it can chemically attack the adjacent phosphodiester bond to cleave the backbone.

RNA is transcribed with only four bases (adenine, cytosine, guanine and uracil), but these bases and attached sugars can be modified in numerous ways as the RNAs mature. Pseudouridine (Ψ), in which the linkage between uracil and ribose is changed from a C–N bond to a C–C bond, and ribothymidine (T) are found in various places (the most notable ones being in the TΨC loop of tRNA). Another notable modified base is hypoxanthine, a deaminated adenine base whose nucleoside is called inosine (I). Inosine plays a key role in the wobble hypothesis of the genetic code.

There are nearly 100 other naturally occurring modified nucleosides, of which pseudouridine and nucleosides with 2'-O-methylribose are the most common. The specific roles of many of these modifications in RNA are not fully understood. However, it is notable that, in ribosomal RNA, many of the post-transcriptional modifications occur in highly functional regions, such as the peptidyl transferase center and the subunit interface, implying that they are important for normal function.

The functional form of single-stranded RNA molecules, just like proteins, frequently requires a specific tertiary structure. The scaffold for this structure is provided by secondary structural elements that are hydrogen bonds within the molecule. This leads to several recognizable "domains" of secondary structure like hairpin loops, bulges, and internal loops. Since RNA is charged, metal ions such as Mg2+ are needed to stabilise many secondary and tertiary structures.

Read more about this topic:  RNA

Other articles related to "structure":

321 Kinematic Structure
321 kinematic structure is a design method for robotic arms (serial manipulators), invented by Donald L ... Many other industrial robots, such as the PUMA, have a kinematic structure that deviates a little bit from the 321 structure ...
Book Of Revelation - Content - Literary Structure
... In terms of literary structure, Revelation consists of four visions, each involving John “seeing” the plan of God unveiled, with an epilogue that concludes the book ... In terms of content, the structure of Revelation is built around four successive groups of seven the messages to the seven churches the seven seals the seven trumpets and the seven bowl judgments ... and phrases of Revelation are organized as a chiastic structure, a literary device used frequently in the Old Testament ...
Zirconium Tungstate - Cubic Phase
... Since the structure is cubic, as described below, the thermal contraction is isotropic - equal in all directions ... The structure of cubic zirconium tungstate consists of corner-sharing ZrO6 octahedral and WO4 tetrahedral structural units ... Unit Modes (RUMs), which involve the coupled rotation of the polyhedral units that make up the structure, and lead to contraction ...
Book Of Ruth - Structure - Ethical Importance
2 ... Loving-kindness living Boaz and Ruth are models of an altruism for which the word "loving-kindness" has been coined (approximately translating Hebrew hesed) ...
Watchmen - Art and Composition - Structure
... The cover of each issue serves as the first panel to the story ... Gibbons said, "The cover of the Watchmen is in the real world and looks quite real, but it's starting to turn into a comic book, a portal to another dimension." The covers were designed as close-ups that focused on a single detail with no human elements present ...

Famous quotes containing the word structure:

    The question is still asked of women: “How do you propose to answer the need for child care?” That is an obvious attempt to structure conflict in the old terms. The questions are rather: “If we as a human community want children, how does the total society propose to provide for them?”
    Jean Baker Miller (20th century)

    One theme links together these new proposals for family policy—the idea that the family is exceedingly durable. Changes in structure and function and individual roles are not to be confused with the collapse of the family. Families remain more important in the lives of children than other institutions. Family ties are stronger and more vital than many of us imagine in the perennial atmosphere of crisis surrounding the subject.
    Joseph Featherstone (20th century)

    There is no such thing as a language, not if a language is anything like what many philosophers and linguists have supposed. There is therefore no such thing to be learned, mastered, or born with. We must give up the idea of a clearly defined shared structure which language-users acquire and then apply to cases.
    Donald Davidson (b. 1917)