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Monday, 07 January 2013
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DNA and RNA - Part 1
DNA and RNA - Part 2
From RNA to Protein Synthesis
RNA Animation
RNA interference (RNAi): by Nature Video
Entering the RNA World
RNA Splicing
LAX | RNA
Ácidos Nucleicos - RNA - Compostos Orgânicos - Prof. Paulo Jubilut
mRNA Processing
RNA Interference
RNA splicing

Rna

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DNA and RNA - Part 1
  • Order:
  • Duration: 12:29
  • Updated: 07 Jan 2013
027 - DNA and RNA - Part 1 - Paul Andersen introduces the nucleic acids of life; RNA and DNA. He details the history of DNA from Griffith, to Avery, to Hershey and finally to Watson and Crick. He also details the difference between prokaryotic and eukaryotic chromosomes.
http://web.archive.org./web/20130108014751/http://wn.com/DNA and RNA - Part 1
DNA and RNA - Part 2
  • Order:
  • Duration: 10:00
  • Updated: 07 Jan 2013
027 - DNA and RNA - Part 2 Paul Andersen continues his description of DNA and RNA. He begins with the structure of DNA and RNA and moves into the process of DNA Replication. He also describes the central dogma of biology explaining how DNA is transcribed to mRNA and is finally translated into proteins. He also introduces genetic engineering and explains how transformation is used to create insulin.
http://web.archive.org./web/20130108014751/http://wn.com/DNA and RNA - Part 2
From RNA to Protein Synthesis
  • Order:
  • Duration: 2:50
  • Updated: 07 Jan 2013
RNA is synthesized from DNA, and enters the ribosome where protein translation and synthesis occurs.
http://web.archive.org./web/20130108014751/http://wn.com/From RNA to Protein Synthesis
RNA Animation
  • Order:
  • Duration: 4:42
  • Updated: 02 Jan 2013
RNA Animation visit my website for more medical animations and their downloads: rufusrajadurai.wetpaint.com
http://web.archive.org./web/20130108014751/http://wn.com/RNA Animation
RNA interference (RNAi): by Nature Video
  • Order:
  • Duration: 5:07
  • Updated: 07 Jan 2013
RNA interference (RNAi) is an important process, used by many different organisms to regulate the activity of genes. This animation explains how RNAi works and introduces the two main players: small interfering RNAs (siRNAs) and microRNAs (miRNAs). We take you on an audio-visual journey, diving into a cell to show how genes are transcribed to make messenger RNA (mRNA) and how RNAi can silence specific mRNAs to stop them from making proteins. The animation is based on the latest research, to give you an up-to-date view. If you'd like to know more about the structures and processes you see in this video, check out the accompanying slideshow: www.nature.com
http://web.archive.org./web/20130108014751/http://wn.com/RNA interference (RNAi): by Nature Video
Entering the RNA World
  • Order:
  • Duration: 58:28
  • Updated: 04 Jan 2013
Nobel Laureate Sidney Altman, Professor of Molecular, Cellular and Developmental Biology at Yale University, gives a general description of the problem of the origin of life on Earth with some detail about what we know now and our knowledge of RNase P, an enzyme with a catalytic RNA subunit. Series: "UC Berkeley Graduate Council Lectures" [12/2010] [Science] [Show ID: 20223]
http://web.archive.org./web/20130108014751/http://wn.com/Entering the RNA World
RNA Splicing
  • Order:
  • Duration: 1:38
  • Updated: 07 Jan 2013
A 3D animation shows the crucial RNA editing step called splicing Originally created for Learn About Spinal Muscular Atrophy ( www.learnaboutsma.org ) TRANSCRIPT: As DNA is transcribed into RNA it needs to be edited to remove non-coding regions, or introns, shown in green. This editing process is called splicing, which involves removing the introns, leaving only the yellow, protein-coding regions, called exons. RNA splicing begins with assembly of helper proteins at the intron/exon borders. These splicing factors act as beacons to guide small nuclear ribo proteins to form a splicing machine, called the spliceosome. The animation is showing this happening in real time. The spliceosome then brings the exons on either side of the intron very close together, ready to be cut. One end of the intron is cut and folded back on itself to join and form a loop. The spliceosome then cuts the RNA to release the loop and join the two exons together. The edited RNA and intron are released and the spliceosome disassembles. This process is repeated for every intron in the RNA. Numerous spliceosomes, shown here in purple, assemble along the RNA. Each spliceosome removes one intron, releasing the loop before disassembling. In this example, three introns are removed from the RNA to leave the complete instructions for a protein.
http://web.archive.org./web/20130108014751/http://wn.com/RNA Splicing
LAX | RNA
  • Order:
  • Duration: 2:05
  • Updated: 04 Jan 2013
Nice new movie from "RNA" the movie maker of "Redesert" hope you enjoy! For more ButtonBashers movies visit www.buttonbashers.com
http://web.archive.org./web/20130108014751/http://wn.com/LAX | RNA
Ácidos Nucleicos - RNA - Compostos Orgânicos - Prof. Paulo Jubilut
  • Order:
  • Duration: 13:16
  • Updated: 07 Jan 2013
★ Mais vídeo aulas? ACESSE: www.biologiatotal.com.br ★ FACEBOOK www.facebook.com ★ TWITTER: twitter.com ★ CONTATO: sitedojubi@gmail.com
  • published: 28 Apr 2012
  • views: 44722
  • author: jubilut
http://web.archive.org./web/20130108014751/http://wn.com/Ácidos Nucleicos - RNA - Compostos Orgânicos - Prof. Paulo Jubilut
mRNA Processing
  • Order:
  • Duration: 2:30
  • Updated: 05 Jan 2013
NDSU Virtual Cell Animations Project animation 'mRNA Processing'. For more information please see vcell.ndsu.edu After being transcribed, mRNA is processed. Before mRNA can be spliced, certain features must be added. These alterations are made during mRNA processing.
http://web.archive.org./web/20130108014751/http://wn.com/mRNA Processing
RNA Interference
  • Order:
  • Duration: 4:06
  • Updated: 03 Jan 2013
RNA interference is a sophisticated mechanism used by cells to regulate gene expression and to protect against viral infection. The discovery of RNAi by Fire and Mello earned them the Nobel Prize.
  • published: 07 May 2010
  • views: 26222
  • author: dolanjw2006
http://web.archive.org./web/20130108014751/http://wn.com/RNA Interference
RNA splicing
  • Order:
  • Duration: 9:07
  • Updated: 06 Jan 2013
Very basic video to describe RNA splicing and then some information on how mRNA can be purified. Not meant to be graduate level information, just an introduction.
http://web.archive.org./web/20130108014751/http://wn.com/RNA splicing
Eine Einführung in RNA Bioinformatik
  • Order:
  • Duration: 5:23
  • Updated: 25 Sep 2012
Diese Video zeigt, warum wir uns am Lehrstuhl für Bioinformatik der Universität Freiburg mit RNA Bioinformatik beschäftigen. Insbesondere erklären wir die Mechanismen von Transkription und Translation und werfen einen Blick auf nicht-kodierende RNAs.
  • published: 15 Oct 2010
  • views: 15269
  • author: RNAFreiburg
http://web.archive.org./web/20130108014751/http://wn.com/Eine Einführung in RNA Bioinformatik
CoD4 | 8it by RNA [Frag Movie]
  • Order:
  • Duration: 6:58
  • Updated: 07 Jan 2013
An amazing Frag Movie. Pure genius! Another Button Bashers classic. RNA: www.youtube.com Let's leave a like, movies like this deserve all of the recognition in the world! --- Hi and guess what? I have finished my movie. Just woke up someday and finished it. It took long time to fight with...
  • published: 26 Sep 2012
  • views: 17391
  • author: WASDGamers
http://web.archive.org./web/20130108014751/http://wn.com/CoD4 | 8it by RNA [Frag Movie]
  • DNA and RNA - Part 1...12:29
  • DNA and RNA - Part 2...10:00
  • From RNA to Protein Synthesis...2:50
  • RNA Animation...4:42
  • RNA interference (RNAi): by Nature Video...5:07
  • Entering the RNA World...58:28
  • RNA Splicing...1:38
  • LAX | RNA...2:05
  • Ácidos Nucleicos - RNA - Compostos Orgânicos - Prof. Paulo Jubilut...13:16
  • mRNA Processing...2:30
  • RNA Interference...4:06
  • RNA splicing...9:07
  • Eine Einführung in RNA Bioinformatik...5:23
  • CoD4 | 8it by RNA [Frag Movie]...6:58
027 - DNA and RNA - Part 1 - Paul Andersen introduces the nucleic acids of life; RNA and DNA. He details the history of DNA from Griffith, to Avery, to Hershey and finally to Watson and Crick. He also details the difference between prokaryotic and eukaryotic chromosomes.

12:29
DNA and RNA - Part 1
027 - DNA and RNA - Part 1 - Paul An­der­sen in­tro­duces the nu­cle­ic acids of life; RNA and D...
pub­lished: 30 Jul 2011
10:00
DNA and RNA - Part 2
027 - DNA and RNA - Part 2 Paul An­der­sen con­tin­ues his de­scrip­tion of DNA and RNA. He begi...
pub­lished: 30 Jul 2011
2:50
From RNA to Pro­tein Syn­the­sis
RNA is syn­the­sized from DNA, and en­ters the ri­bo­some where pro­tein trans­la­tion and syn­thes...
pub­lished: 11 Mar 2007
4:42
RNA An­i­ma­tion
RNA An­i­ma­tion visit my web­site for more med­i­cal an­i­ma­tions and their down­loads: ru­fus­ra­jad...
pub­lished: 10 May 2007
5:07
RNA in­ter­fer­ence (RNAi): by Na­ture Video
RNA in­ter­fer­ence (RNAi) is an im­por­tant pro­cess, used by many dif­fer­ent or­gan­isms to regul...
pub­lished: 16 Dec 2011
58:28
En­ter­ing the RNA World
Nobel Lau­re­ate Sid­ney Alt­man, Pro­fes­sor of Molec­u­lar, Cel­lu­lar and De­vel­op­men­tal Bi­ol­o­gy a...
pub­lished: 10 Jan 2011
1:38
RNA Splic­ing
A 3D an­i­ma­tion shows the cru­cial RNA edit­ing step called splic­ing Orig­i­nal­ly cre­at­ed for L...
pub­lished: 13 Apr 2012
2:05
LAX | RNA
Nice new movie from "RNA" the movie maker of "Re­desert" hope you enjoy! For more But­ton­Bas...
pub­lished: 27 Jan 2010
13:16
Ácidos Nu­cle­icos - RNA - Com­pos­tos Orgânicos - Prof. Paulo Ju­bi­lut
★ Mais vídeo aulas? ACESSE: www.​biologiatotal.​com.​br ★ FACE­BOOK www.​facebook.​com ★ TWIT­TER...
pub­lished: 28 Apr 2012
au­thor: ju­bi­lut
2:30
mRNA Pro­cess­ing
NDSU Vir­tu­al Cell An­i­ma­tions Pro­ject an­i­ma­tion 'mRNA Pro­cess­ing'. For more in­for­ma­tion ple...
pub­lished: 03 Mar 2008
4:06
RNA In­ter­fer­ence
RNA in­ter­fer­ence is a so­phis­ti­cat­ed mech­a­nism used by cells to reg­u­late gene ex­pres­sion an...
pub­lished: 07 May 2010
au­thor: dolan­jw2006
9:07
RNA splic­ing
Very basic video to de­scribe RNA splic­ing and then some in­for­ma­tion on how mRNA can be pur...
pub­lished: 30 Apr 2009
au­thor: Greg Pe­tersen
5:23
Eine Einführung in RNA Bioin­for­matik
Diese Video zeigt, warum wir uns am Lehrstuhl für Bioin­for­matik der Uni­ver­sität Freiburg m...
pub­lished: 15 Oct 2010
au­thor: RNAFreiburg
6:58
CoD4 | 8it by RNA [Frag Movie]
An amaz­ing Frag Movie. Pure ge­nius! An­oth­er But­ton Bash­ers clas­sic. RNA: www.​youtube.​com L...
pub­lished: 26 Sep 2012
au­thor: WAS­DGamers
Youtube results:
7:28
Sci­en­tists Win Lasker for mi­cro-RNA Dis­cov­ery
The Lasker Foun­da­tion has an­nounced that Doc­tors Vic­tor Am­bros, Gary Ru­vkun, and David Bau...
pub­lished: 17 Sep 2008
2:55
mRNA Splic­ing
NDSU Vir­tu­al Cell An­i­ma­tions Pro­ject an­i­ma­tion 'mRNA Splic­ing'. For more in­for­ma­tion pleas...
pub­lished: 03 Mar 2008
1:48
siRNA Pathway.​flv
small in­ter­fer­ing RNAs (siR­NAs) are 21--23nt dsRNA (dou­ble-strand­ed RNA) molecules that fa...
pub­lished: 07 Dec 2010
au­thor: Saroj Sahu
4:54
RNA In­ter­fer­ence (RNAi)
RNA In­ter­fer­ence (RNAi) mech­a­nism in worms and plants. Cre­at­ed for Na­ture Re­views Ge­net­ics...
pub­lished: 30 Mar 2008
photo: UN / Evan Schneider
File - Cristina Fernández, President of Argentina, is pictured during a meeting of the UN’s Special Committee on Decolonization to consider the “Question of the Falkland Islands (Malvinas)”, 14 June, 2012.
Pittsburgh Post-Gazette
06 Jan 2013
LONDON -- They have barely 3,000 inhabitants and far more sheep than people. They are more than 8,700 miles from London. For much of the year, they are bitterly cold and wind-swept, with only open sea and ice between them and Antarctica ... But the Falkland Islands, the focus of a short war between Britain and Argentina in 1982, have been in the headlines again recently ... Their arguments suggest what has long been evident ... Ms ... Mr ... Cameron said....(size: 5.1Kb)
photo: WN / Imran Nissar
Indian Army soldiers patrol outside their army camp at Gurez, about 180 kilometers (113 miles) north of Srinagar, India, Saturday, Aug. 20, 2011. Indian troops in Kashmir fought a deadly gunbattle with suspected rebels crossing the military Line of Control from Pakistani-controlled territory Saturday, the army said. One soldier and 11 suspected rebels were killed, army spokesman Lt. Col. J.S. Brar said, but only six suspected rebels' bodies were recovered. He said the other five bodies were lost when they fell into a river during the fighting in the disputed Himalayan region.
Herald Tribune
06 Jan 2013
ISLAMABAD - The Pakistani military is accusing forces from neighboring India of crossing the boundary between the two sides' forces in Kashmir and attacking a Pakistani border post, killing a soldier. The military's public relations office said in a statement Sunday that another Pakistani soldier was critically wounded in the incident early Sunday. They said troops are still exchanging gunfire in the area ... All rights reserved ... Parker ... ....(size: 4.3Kb)
photo: AP / Joerg Koch
Eine Ein-Euro-Muenze steht in Muenchen in einer Fotoillustration auf einem Ein-Dollar-Schein (Foto vom 28.11.07).
Project Syndicate
07 Jan 2013
NEW YORK – In the shadow of the euro crisis and America’s fiscal cliff, it is easy to ignore the global economy’s long-term problems. But, while we focus on immediate concerns, they continue to fester, and we overlook them at our peril. The most serious is global warming. While the global economy’s weak performance has led to a corresponding slowdown in the increase in carbon emissions, it amounts to only a short respite ... ....(size: 5.3Kb)
photo: US Army / Sgt. Christopher Bonebrake
File - U.S. Army Pfc. Caesar Pimentel, an infantryman attached to 3rd Platoon, Company B, 1st Battalion, 187th Infantry Regiment, 3rd Brigade Combat Team, 101st Airborne Division (Air Assault), the security forces element for Provincial Reconstruction Team Paktiya, keeps a watchful eye on his surroundings in the Sayed Karem District market, Afghanistan, Dec. 20, 2012.
WorldNews.com
07 Jan 2013
Article by WN.com Correspondent Dallas Darling. When Congress granted President Lyndon B. Johnson absolute powers to "take all necessary measures to repel any armed attack against the forces of the United States and to prevent further aggression," Congress could have also included "all necessary vanities." The 1964 Gulf of Tonkin Resolution, which greatly escalated a foreign imperial war in Vietnam, added fuel to the bonfires of vanity....(size: 5.2Kb)
photo: WN / Imran Nissar
Kashmiri Sikh students shout slogans and hold placards as they take part in a protest in Srinagar on December 27, 2012, following the rape of a student in the Indian capital on December 16. An Indian student who was left fighting for her life after being brutally gang raped on a bus in New Delhi arrived December 27 in Singapore for treatment at a leading hospital. The attack sparked a wave of protests across India in which a policeman died and more than 100 police and protestors were injured.
Al Jazeera
07 Jan 2013
The father of Indian woman who died after being gang raped and tortured has said he had not allowed his daughter to be identified after the British Daily Mirror Sunday paper edition revealed her name, Indian newspaper the Hindustan Times reported on Monday ... Legal experts say the court in the Saket district of the capital would likely transfer the case to a more senior court during Monday's hearing ... 614 Source.....(size: 19.4Kb)



noodls
08 Jan 2013
(Source. Energex Ltd). 8 January 2013 ... "The regeneration of RNA Showgrounds and expansion of the Herston hospitals and medical research precinct - along with a range of other local projects - will place a much greater demand on the electricity network, and this upgrade ensures we keep up with local development ... Mr Madigan thanked the local community in advance for their patience during the upgrades ... distributed by ... (noodl. 17128291) ....(size: 3.8Kb)
PR Newswire
07 Jan 2013
ethris GmbH and Shire today announce the initiation of a research based alliance focused on the development and commercialization of novel RNA-based therapeutics ... Christian Plank , have developed a novel RNA modification technology that creates Stable and Non-Immunogenic Messenger RNA (SNIM®-RNA) molecules that are ideally suited for use in protein replacement therapies to treat monogenic genetic diseases....(size: 5.1Kb)
noodls
07 Jan 2013
By contrast, the new technique uses a single protein that requires only a short RNA molecule to program it for site-specific DNA recognition, Doudna said ... "It (the Cas9-RNA complex) is easier to make than TALEN proteins, and it's smaller," making it easier to slip into cells and even to program hundreds of snips simultaneously, he said ... Doudna and her team worked out the details of how the enzyme-RNA complex cuts DNA....(size: 7.8Kb)
Seeking Alpha
07 Jan 2013
Treatment with ACH-3102 has resulted in rapid reduction in HCV RNA accompanied by normalization of liver enzymes ... (100%) RVR = HCV RNA < LLOQ (< 25 IU/mL) at week 4 ETR = HCV RNA < LLOD (< 10 IU/mL) at week 12 *RVR ... 3 subjects had HCV RNA undetectable at week 4 and 1 subject had HCV RNA undetectable at week 3, HCV RNA < 25 IU/ml (detectable....(size: 10.4Kb)
noodls
07 Jan 2013
Treatment with ACH-3102 has resulted in rapid reduction in HCV RNA accompanied by normalization of liver enzymes ...  (100%) RVR = HCV RNA < LLOQ ( < 25 IU/mL) at week 4 ETR = HCV RNA < LLOD ( < 10 IU/mL) at week 12 *RVR ... 3 subjects had HCV RNA undetectable at week 4 and 1 subject had HCV RNA undetectable at week 3, HCV RNA < 25 IU/ml (detectable....(size: 12.1Kb)
PR Newswire
07 Jan 2013
7, 2013 /PRNewswire/ -- Santaris Pharma A/S, a clinical-stage biopharmaceutical company focused on the discovery and development of RNA-targeted therapies, today announced that the USPTO has issued an Order granting their request for inter-partes re-examination of US patent 7,838,504 (the '504 patent), in the name of The Board of Trustees of the Leland Stanford Junior University, and licensed to Regulus Therapeutics Inc. ....(size: 6.2Kb)
PhysOrg
07 Jan 2013
But something mysterious happens to introns during the final processing of messenger RNA (mRNA), the genetic blueprint that's sent from the cell's nucleus to its protein factory ... Following completion of the genome sequencing projects, subsequent DNA and RNA sequencing revealed the existence of more than one splice variant, or isoform, for 90 percent of human genes....(size: 4.3Kb)
The Examiner
07 Jan 2013
Forever Young ... What happens when a real-life company touts their skin product as Forever Young? Well, women (and men) all over the world should take notice ... In this case, rejuvenation is achieved by altering gene expression. With regular treatments, the RNA expression will more closely resemble young skin ... ....(size: 1.5Kb)
noodls
07 Jan 2013
(Source. NIH - National Institutes of Health). Embargoed for Release. Sunday, January 6, 2013. 1 p.m. EST Contact.. NCI Press Office. 301-496-6641 ... 6, 2013 ... To find the new gene, the investigators used a technology involving RNA sequencing on human liver cells treated to mimic hepatitis C virus infection. "By using RNA sequencing we looked outside the box to search for something beyond what was already known in this region ... Reference ... Jan....(size: 6.6Kb)
PhysOrg
07 Jan 2013
By controlling the transcription of DNA into messenger RNA, TFIID forms the cornerstone of the machinery that controls gene expression in our cells. Despite its crucial role, very little was known about its architecture. TFIID is present at very low levels in cells, and it is a very large protein complex made of 20 subunits ... This video is not supported by your browser at this time ... ....(size: 2.3Kb)
noodls
07 Jan 2013
(Source. ASU - Arizona State University). Posted. January 07, 2013. The Origins Project at Arizona State University is planning two interactive, virtual events with visiting professors this semester. Both visiting professors - Frank Wilczek and Sidney Altman - are Nobel laureates ... Wilczek, Gross and H ... Altman shared the 1989 Nobel Prize in chemistry with Thomas Cech for their work on the catalytic properties of RNA ... 480-965-4823 ... (noodl....(size: 3.7Kb)
StreetInsider
07 Jan 2013
Tweet. Get Alerts ACHN Hot Sheet. Price. $9.45 --0%. Overall Analyst Rating.. &nbsp;   BUY ( Up). Revenue Growth %. -100.0%. Achillion Pharmaceuticals, Inc. (Nasdaq ... The initial cohort enrolled eight patients with GT 1b HCV, IL28b genotype CC, that are receiving twelve weeks of ACH-3102 once daily in combination with ribavirin ... Treatment with ACH-3102 has resulted in rapid reduction in HCV RNA accompanied by normalization of liver enzymes....(size: 3.1Kb)
Fox News
07 Jan 2013
Currently, 29 states and New York City are reporting high levels of influenza-like-illness (ILI), and another nine states are reporting moderate levels of ILI. This season, 18 children have died from flu-associated deaths. Related. Flu season in full swing; could get worse. Influenza is a tiny frequently mutating package of genetic material (RNA) surrounded by an envelope ... The severity of flu seasons vary, based on the type of flu ... Dr ... ....(size: 4.0Kb)
A hairpin loop from a pre-mRNA. Highlighted are the nucleobases (green) and the ribose-phosphate backbone (blue).

Ribonucleic acid /rbɵ.njuːˌkl.ɨk ˈæsɪd/, or RNA, is part of a group of molecules known as the nucleic acids, which are one of the four major macromolecules (along with lipids, carbohydrates and proteins) essential for all known forms of life. Like DNA, RNA is made up of a long chain of components called nucleotides. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate group. The sequence of nucleotides allows RNA to encode genetic information. All cellular organisms use messenger RNA (mRNA) to carry the genetic information that directs the synthesis of proteins. In addition, many viruses use RNA instead of DNA as their genetic material.

Some RNA molecules play an active role in cells by catalyzing biological reactions, controlling gene expression, or sensing and communicating responses to cellular signals. One of these active processes is protein synthesis, a universal function whereby mRNA molecules direct the assembly of proteins on ribosomes. This process uses transfer RNA (tRNA) molecules to deliver amino acids to the ribosome, where ribosomal RNA (rRNA) links amino acids together to form proteins.

The chemical structure of RNA is very similar to that of DNA, with two differences: (a) RNA contains the sugar ribose, while DNA contains the slightly different sugar deoxyribose (a type of ribose that lacks one oxygen atom), and (b) RNA has the nucleobase uracil while DNA contains thymine. Unlike DNA, most RNA molecules are single-stranded and can adopt very complex three-dimensional structures.

Contents

Comparison with DNA[link]

Three-dimensional representation of the 50S ribosomal subunit. RNA is in ochre, protein in blue. The active site is in the middle (red).

RNA and DNA are both nucleic acids, but differ in three main ways:

  • Unlike double-stranded DNA, RNA is a single-stranded molecule in many of its biological roles and has a much shorter chain of nucleotides.
  • While DNA contains deoxyribose, RNA contains ribose (in deoxyribose there is no hydroxyl group attached to the pentose ring in the 2' position). These hydroxyl groups make RNA less stable than DNA because it is more prone to hydrolysis.
  • The complementary base to adenine is not thymine, as it is in DNA, but rather uracil, which is an unmethylated form of thymine.[1]

Like DNA, most biologically active RNAs, including mRNA, tRNA, rRNA, snRNAs, and other non-coding RNAs, contain self-complementary sequences that allow parts of the RNA to fold[2] and pair with itself to form double helices. Analysis of these RNAs has revealed that they are highly structured. Unlike DNA, their structures do not consist of long double helices but rather collections of short helices packed together into structures akin to proteins. In this fashion, RNAs can achieve chemical catalysis, like enzymes.[3] For instance, determination of the structure of the ribosome—an enzyme that catalyzes peptide bond formation—revealed that its active site is composed entirely of RNA.[4]

Structure[link]

Watson-Crick base pairs in a siRNA (hydrogen atoms are not shown)

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.[5] However, other interactions are possible, such as a group of adenine bases binding to each other in a bulge,[6] or the GNRA tetraloop that has a guanine–adenine base-pair.[5]

Chemical structure of RNA

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.[7] This results in a very deep and narrow major groove and a shallow and wide minor groove.[8] 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.[9]

RNA is transcribed with only four bases (adenine, cytosine, guanine and uracil),[10] 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).[11] 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.[12]

There are nearly 100 other naturally occurring modified nucleosides,[13] of which pseudouridine and nucleosides with 2'-O-methylribose are the most common.[14] 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.[15]

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.[16] Since RNA is charged, metal ions such as Mg2+ are needed to stabilise many secondary and tertiary structures.[17]

Synthesis[link]

Synthesis of RNA is usually catalyzed by an enzyme—RNA polymerase—using DNA as a template, a process known as transcription. Initiation of transcription begins with the binding of the enzyme to a promoter sequence in the DNA (usually found "upstream" of a gene). The DNA double helix is unwound by the helicase activity of the enzyme. The enzyme then progresses along the template strand in the 3’ to 5’ direction, synthesizing a complementary RNA molecule with elongation occurring in the 5’ to 3’ direction. The DNA sequence also dictates where termination of RNA synthesis will occur.[18]

RNAs are often modified by enzymes after transcription. For example, a poly(A) tail and a 5' cap are added to eukaryotic pre-mRNA and introns are removed by the spliceosome.

There are also a number of RNA-dependent RNA polymerases that use RNA as their template for synthesis of a new strand of RNA. For instance, a number of RNA viruses (such as poliovirus) use this type of enzyme to replicate their genetic material.[19] Also, RNA-dependent RNA polymerase is part of the RNA interference pathway in many organisms.[20]

Types of RNA[link]

Overview[link]

Structure of a hammerhead ribozyme, a ribozyme that cuts RNA

Messenger RNA (mRNA) is the RNA that carries information from DNA to the ribosome, the sites of protein synthesis (translation) in the cell. The coding sequence of the mRNA determines the amino acid sequence in the protein that is produced.[21] Many RNAs do not code for protein however (about 97% of the transcriptional output is non-protein-coding in eukaryotes [22][23][24][25]).

These so-called non-coding RNAs ("ncRNA") can be encoded by their own genes (RNA genes), but can also derive from mRNA introns.[26] The most prominent examples of non-coding RNAs are transfer RNA (tRNA) and ribosomal RNA (rRNA), both of which are involved in the process of translation.[1] There are also non-coding RNAs involved in gene regulation, RNA processing and other roles. Certain RNAs are able to catalyse chemical reactions such as cutting and ligating other RNA molecules,[27] and the catalysis of peptide bond formation in the ribosome;[4] these are known as ribozymes.

In translation[link]

Messenger RNA (mRNA) carries information about a protein sequence to the ribosomes, the protein synthesis factories in the cell. It is coded so that every three nucleotides (a codon) correspond to one amino acid. In eukaryotic cells, once precursor mRNA (pre-mRNA) has been transcribed from DNA, it is processed to mature mRNA. This removes its introns—non-coding sections of the pre-mRNA. The mRNA is then exported from the nucleus to the cytoplasm, where it is bound to ribosomes and translated into its corresponding protein form with the help of tRNA. In prokaryotic cells, which do not have nucleus and cytoplasm compartments, mRNA can bind to ribosomes while it is being transcribed from DNA. After a certain amount of time the message degrades into its component nucleotides with the assistance of ribonucleases.[21]

Transfer RNA (tRNA) is a small RNA chain of about 80 nucleotides that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. It has sites for amino acid attachment and an anticodon region for codon recognition that binds to a specific sequence on the messenger RNA chain through hydrogen bonding.[26]

Ribosomal RNA (rRNA) is the catalytic component of the ribosomes. Eukaryotic ribosomes contain four different rRNA molecules: 18S, 5.8S, 28S and 5S rRNA. Three of the rRNA molecules are synthesized in the nucleolus, and one is synthesized elsewhere. In the cytoplasm, ribosomal RNA and protein combine to form a nucleoprotein called a ribosome. The ribosome binds mRNA and carries out protein synthesis. Several ribosomes may be attached to a single mRNA at any time.[21] Nearly all the RNA found in a typical eukaryotic cell is rRNA.

Transfer-messenger RNA (tmRNA) is found in many bacteria and plastids. It tags proteins encoded by mRNAs that lack stop codons for degradation and prevents the ribosome from stalling.[28]

Regulatory RNAs[link]

Several types of RNA can downregulate gene expression by being complementary to a part of an mRNA or a gene's DNA. MicroRNAs (miRNA; 21-22 nt) are found in eukaryotes and act through RNA interference (RNAi), where an effector complex of miRNA and enzymes can cleave complementary mRNA, block the mRNA from being translated, or accelerate its degradation.[29][30] While small interfering RNAs (siRNA; 20-25 nt) are often produced by breakdown of viral RNA, there are also endogenous sources of siRNAs.[31][32]

siRNAs act through RNA interference in a fashion similar to miRNAs. Some miRNAs and siRNAs can cause genes they target to be methylated, thereby decreasing or increasing transcription of those genes.[33][34][35] Animals have Piwi-interacting RNAs (piRNA; 29-30 nt) that are active in germline cells and are thought to be a defense against transposons and play a role in gametogenesis.[36][37]

Many prokaryotes have CRISPR RNAs, a regulatory system similar to RNA interference.[38] Antisense RNAs are widespread; most downregulate a gene, but a few are activators of transcription.[39] One way antisense RNA can act is by binding to an mRNA, forming double-stranded RNA that is enzymatically degraded.[40] There are many long noncoding RNAs that regulate genes in eukaryotes,[41] one such RNA is Xist, which coats one X chromosome in female mammals and inactivates it.[42]

An mRNA may contain regulatory elements itself, such as riboswitches, in the 5' untranslated region or 3' untranslated region; these cis-regulatory elements regulate the activity of that mRNA.[43] The untranslated regions can also contain elements that regulate other genes.[44]

In RNA processing[link]

Uridine to pseudouridine is a common RNA modification.

Many RNAs are involved in modifying other RNAs. Introns are spliced out of pre-mRNA by spliceosomes, which contain several small nuclear RNAs (snRNA),[1] or the introns can be ribozymes that are spliced by themselves.[45] RNA can also be altered by having its nucleotides modified to other nucleotides than A, C, G and U. In eukaryotes, modifications of RNA nucleotides are in general directed by small nucleolar RNAs (snoRNA; 60-300 nt),[26] found in the nucleolus and cajal bodies. snoRNAs associate with enzymes and guide them to a spot on an RNA by basepairing to that RNA. These enzymes then perform the nucleotide modification. rRNAs and tRNAs are extensively modified, but snRNAs and mRNAs can also be the target of base modification.[46][47] RNA can also be methylated.[48][49]

RNA genomes[link]

Like DNA, RNA can carry genetic information. RNA viruses have genomes composed of RNA that encodes a number of proteins. The viral genome is replicated by some of those proteins, while other proteins protect the genome as the virus particle moves to a new host cell. Viroids are another group of pathogens, but they consist only of RNA, do not encode any protein and are replicated by a host plant cell's polymerase.[50]

In reverse transcription[link]

Reverse transcribing viruses replicate their genomes by reverse transcribing DNA copies from their RNA; these DNA copies are then transcribed to new RNA. Retrotransposons also spread by copying DNA and RNA from one another,[51] and telomerase contains an RNA that is used as template for building the ends of eukaryotic chromosomes.[52]

Double-stranded RNA[link]

Double-stranded RNA (dsRNA) is RNA with two complementary strands, similar to the DNA found in all cells. dsRNA forms the genetic material of some viruses (double-stranded RNA viruses). Double-stranded RNA such as viral RNA or siRNA can trigger RNA interference in eukaryotes, as well as interferon response in vertebrates.[53][54][55]

Key discoveries in RNA biology[link]

Robert W. Holley, left, poses with his research team.

Research on RNA has led to many important biological discoveries and numerous Nobel Prizes. Nucleic acids were discovered in 1868 by Friedrich Miescher, who called the material 'nuclein' since it was found in the nucleus.[56] It was later discovered that prokaryotic cells, which do not have a nucleus, also contain nucleic acids. The role of RNA in protein synthesis was suspected already in 1939.[57] Severo Ochoa won the 1959 Nobel Prize in Medicine (shared with Arthur Kornberg) after he discovered an enzyme that can synthesize RNA in the laboratory.[58] However, the enzyme discovered by Ochoa (polynucleotide phosphorylase) was later shown to be responsible for RNA degradation, not RNA synthesis.

The sequence of the 77 nucleotides of a yeast tRNA was found by Robert W. Holley in 1965,[59] winning Holley the 1968 Nobel Prize in Medicine (shared with Har Gobind Khorana and Marshall Nirenberg). In 1967, Carl Woese hypothesized that RNA might be catalytic and suggested that the earliest forms of life (self-replicating molecules) could have relied on RNA both to carry genetic information and to catalyze biochemical reactions—an RNA world.[60][61]

During the early 1970s, retroviruses and reverse transcriptase were discovered, showing for the first time that enzymes could copy RNA into DNA (the opposite of the usual route for transmission of genetic information). For this work, David Baltimore, Renato Dulbecco and Howard Temin were awarded a Nobel Prize in 1975. In 1976, Walter Fiers and his team determined the first complete nucleotide sequence of an RNA virus genome, that of bacteriophage MS2.[62]

In 1977, introns and RNA splicing were discovered in both mammalian viruses and in cellular genes, resulting in a 1993 Nobel to Philip Sharp and Richard Roberts. Catalytic RNA molecules (ribozymes) were discovered in the early 1980s, leading to a 1989 Nobel award to Thomas Cech and Sidney Altman. In 1990 it was found in petunia that introduced genes can silence similar genes of the plant's own, now known to be a result of RNA interference.[63][64]

At about the same time, 22 nt long RNAs, now called microRNAs, were found to have a role in the development of C. elegans.[65] Studies on RNA interference gleaned a Nobel Prize for Andrew Fire and Craig Mello in 2006, and another Nobel was awarded for studies on transcription of RNA to Roger Kornberg in the same year. The discovery of gene regulatory RNAs has led to attempts to develop drugs made of RNA, such as siRNA, to silence genes.[66]

See also[link]

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External links[link]

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