Today, barcodes conceived by Bernard Silver, a graduate student at Drexel Institute of Technology in Philadelphia, PA, and his friends Norman Woodland and Jordin Johanson in 1948 are used universally. They play a critical role for identification purposes, relational information, and tracking. They are especially useful because scanners are relatively inexpensive, extremely accurate and highly efficient at obtaining and transmitting information from barcodes and their databases.
Natural barcodes (a short strand of deoxyribonucleic acid (DNA) (the genetic code unique to each living organism and some viruses) that consists of between 300-800 base pairs (bps) - Adenine (A)-Thymidine (T), and Cytosine (C)-Guanine (G)) that can be represented by different colors) also exist and are well established in the animal kingdom. Through sequencing of the cytochrome oxidase 1 (CO1) gene (inspired by biologist Paul Hebert's futile efforts dating back to the 1970s to identify 2000 species of moth in Papua New Guinea (because of their taxonomic and morphological similarities), his "retreat to water fleas" (of which there are only 200 species) and subsequent 2003 paper in which he described "the diversity of life as a 'harsh burden' to biologists" and suggested, "every species on Earth... be assigned a simple DNA bar code so it would be easy to tell them apart" as written in Scanning Life (National Geographic, May 2010)), which is present in the mitochondrial DNA of every multi-cellular organism, scientists are able to readily determine phylogeny (identification) on a molecular level and store it in databases for easy retrieval. Per P.M. Hollingsworth, DNA bar-coding plants in biodiversity hot spots: Progress and outstanding questions (Heredity, 9 April 2008) "DNA bar-coding is now routinely used for organismal identification" in animals and "has contributed to the discovery of new species."
However, per Mark W. Chase, Nicolas Salamin, Mike Wilkinson, James M. Dunwell, Rao Prasad Kesanakurthi, Nadia Haidar, and Vincent Savolainen, Land plants and DNA barcodes: short-term and long-term goals (Philosophical Transactions Of The Royal Society, 2005) this has not been the case with plants until recently since their CO1 gene does not have the ability to serve as a barcode gene and because they "have had the reputation of being problematic for DNA bar-coding" due to "low levels of variability" and lack of variation in "plastid phylogenetic markers." This view prevailed until 2008 when a team led by Dr. Vincent Savolainen of Imperial College London's Department of Life Sciences and The Royal Botanic Gardens, Kew, studied the functionality of the megakaryocyte-associated tyrosine-protein kinase (matK) gene located in the intron of trnK chloroplast genes found in plant leaves. Their research found that the matK gene (which "contained significant species-level genetic variability and divergence, conserved flanking sites for developing PCR (polymerase chain reaction, a process that enables scientists to produce millions of copies of a specific DNA sequence in about two hours while bypassing the need to use bacteria to amplify DNA) primers for wide taxonomic application, [and] a short sequence length... to facilitate... DNA extraction and amplification") as reported by W. John Kress and David L. Erickson, DNA barcodes: Genes, genomics, and bioinformatics (PNAS. Vol. 105, No. 8. 26 February 2008) and in Polymerase Chain Reaction (PCR) (Gene Almanac. Dolan DNA Learning Center and Cold Spring Harbor Laboratory, Inc. 2009) could be used to differentiate between at least 90% of all plants, including those that appeared identical to the human eye, known as cryptic species because of their identical appearance and genetic differences.
The matK gene, though, was found ineffective in distinguishing between up to 10% of plant species because of two major factors:
1. When variation resulting from "rapid bursts of speciation" was small, and
2. Based on Anna-Marie Lever's article, DNA 'barcode' revealed in plants (BBC News, 6 February 2008), when plants were hybrids whose genome was rearranged through natural and artificial cross-breeding, which "confuse[d] matK gene information"
When discovery that the matK gene could serve as a natural barcode in plants was made, its location was consistent with that in animals - the barcode genes in both are located in cellular energy centers outside the nucleus (mitochondria serve as "tiny powerhouses" in animal cells while chloroplasts are involved in plant photosynthesis) since per Anna-Marie Lever, DNA 'barcode' revealed in plants, "nuclear genes usually evolve too rapidly to distinguish between [organisms] of the same species." However, consistent with mitochronidrial genes in animals, "chloroplast genes [in plants] evolve at a slower rate, allowing for [distinguishment between the same species, and] fast enough for differences to occur in the DNA code between species."
The only exception between plants and animals is the range of effectiveness for their respective barcode genes. The CO1 gene can be effectively used to determine and record phylogeny in nearly 100% of animal species while the matK gene is ineffective in about 10% of plant species. The key reason for the 90% effective range with regard to the matK gene can be attributed to natural crossbreeding, which is significantly more common to plants than animals. Because of this, matK gene information needs to be supplemented by data from another gene. Although studies utilizing trnH-psbA genes that share similar characteristics to matK showed promise (when sequencing of matK and trnH-psbA was utilized involving plants of the nutmeg family (Myristicaceae) the effective range for correct identification rose to approximately 95%), a panel of 52 leading barcoding scientists opted on using the ribulose-bisphosphate carboxylase (rbcL) gene (also located in plant chloroplasts) outlined in a 2009 paper published in Proceedings of the National Academy of Sciences as reported by Daniel Cressey, DNA barcodes for plants a step closer (Nature, 27 July 2009), to effectively complete the barcode for the 10% group.
While discovery of the phylogenetic usefulness of the matK gene is relatively novel, studies indicating the phylogenetic usefulness of the rbcL gene date back as far as 1986 when Jane Aldrich, Barry Cherney, Ellis Merlin and Jeff Palmer reported in Nucleic Acids Research that sequencing of rbcL genes showed petunia and tobacco and alfalfa and peas are 97.3% and 94.1% genetically identical when comparing their bps.
Additional studies, to name two, added further evidence of the phylogenetic usefulness of the rbcL gene. One, reported by Mitsuyasu Hasebe, Tomokyuki Omori, Miyuki Nakazawa, Toshio Sano, Masahiro Kato, and Kunio Iwatsuki in rbcL Gene sequences provide evidence for the evolutionary lineages of leptosporangiate ferns (Proceedings of the National Academy of Sciences, June 1994) utilized PCR-amplified rbcL fragments in 58 species of leptosporangiate ferns, which belong to the pteridophyte class (vascular plants that produce spores to reproduce in lieu of flowers and seeds) which has the longest evolutionary history of any vascular land plant (consequently enduring the greatest loss of plylogentically useful data) to capture their evolutionary links. The other, reported by Hiroaki Setoguchi, Takeshi Asakawa Osawa, Jean-Christophe Pintaud, Tanguy Jaffré, and Jean-Marie Veillon in Phylogenetic relationships within Araucariaceae based on rbcL gene sequences (American Journal of Botany, 1998) utilized rbcL gene sequencing to successfully determine the pylogenetic relationship between 29 species of Araucariaceae (a sample representing nearly every existing species of the ancient family of conifers that achieved maximum diversification during the Jurassic (c. 199.6± 0.6 to 145.5± 4 million years ago (Ma) and Cretaceous periods (c. 145.5 ± 4 to 65.5 ± 0.3 Ma)).
During the study that led to the discovery that a plant's matK gene could serve as a primary barcode gene, Dr. Savolainen's team compared eight potential candidate genes and analyzed more than 1600 plant DNA samples obtained from the tropical forests of Costa Rica and the temperate region of Kruger National Park, South Africa, two of the world's leading biodiversity hotspots.
Through sequencing of the matK gene (which has a slightly different code for plants of different species and a near identical code for plants of the same species), they were able to distinguish between a thousand orchid species - plants known for their difficulty to differentiate because of their near identical appearance, especially when sterile. Consequently, per Plant DNA 'Barcode' identified (Medical News Today, 6 February 2008), "...what was previously assumed to be one species of orchid was [found to be] two distinct species that live on different slopes of the mountains [with] differently shaped flowers adapted for different pollinating insects."
Scientific analysis, in which the matK gene was divided into five sectors has determined that the sector 3 (known as 3') region is the most effective area in providing useful phylogenetic information. When broken down further, 140 out of the 306 bps of the 3' region were phylogenetically informative.
Establishment of the matK gene's barcode function supplemented by use of the rbcL gene, represents a major breakthrough in plant science since it offers a diverse range of potential applications that can be used by scientists and plant taxonomists/systematists as well as an opportunity to close the large gap that presently exists between plant and animal barcoding.
Such potential applications include but are not limited to:
1. Accurate identification of plant species, especially those of cryptic species that are difficult to differentiate that could potentially lead to discovery of new species. Presently as stated by Anna-Marie Lever, DNA 'barcode' revealed in plants only a "few experts [can] accurately identify the plant composition of biodiverse hotspots."
2. Accurate identification of botanic components in foods and medicines.
3. Detection of undesirable plant material in processed foods by health inspectors.
4. Tracking of plant species (e.g. migration).
5. Locating of endangered species for habitat preservation.
6. Detection of illegal transport/trade of endangered species to protect them from potential harm.
7. Confirmation or identification of plant-insect associations.
8. Expansion and facilitation of botanical medical research.
However, before this can be achieved, the following steps must be taken:
1. Establishment of a genetic database that can be uploaded into a portable scanner so that data can be readily available based on the analysis of a mere leaf/tissue sample. To enhance identification of known species and speed up discovery of new species, such a database must be massive and available online.
2. Establishment of a search method or algorithm to search and access DNA barcode information from an online database.
3. Establishment of a set of reference standards (which includes barcoding based solely on bp extractions from matK and rbcL genes) utilizing existing plant DNA specimens held at botanical gardens, herbariums, museums and other DNA repositories. For example, the Consortium for the Barcode of Life based at the Smithsonian Institution's National Museum of Natural History in Washington, D.C. has identified over two million of the estimated ten million species of plants, animals, and fungi (many still unnamed) while the Royal Botanic Gardens, Kew currently holds 23,000+ plant DNA samples. This is especially important since fresh collection efforts aimed at obtaining the DNA of every plant species, are impractical since they would require significant effort and time.
4. Collection efforts conducted in accordance with international laws (e.g. Convention of Biological Diversity) to protect habitats and ensure specimen integrity. Per W. John Kress and David L. Erickson, DNA barcodes: Genes, genomics, and bioinformatics, such collection efforts are necessary since existing specimens are limited in quantity and may consist of degraded DNA. Currently collection efforts are being made in temperate (Plummers Island, MD and New York City, among others) and tropical (Forest Dynamics Plot, Panama, among others) regions.
With a stamp of approval from the United Nations that declared 2010 "the International Year of Biodiversity," vigorous global efforts aimed at barcoding 500,000 out of the 1.7 million named species of plants, animals, and fungi by 2015, are being pursued by international teams of scientists as well as by groups/projects such as the Consortium for the Barcode of Life and soon, the International Barcode of Life (iBol) project, which is slated to launch in July 2010. Furthermore, Paul Hebert, the biologist who inspired the barcode movement and a major participant in the iBol project, per Scanning Life (National Geographic, May 2010) declared, "the approach is scalable to the planet [so that by 2025 every] species humans encounter frequently will [have been] barcoded."
With regard to plants, as technology is enhanced to exploit the genetic code of matK and rbcL genes through the establishment of a uniform database, production of inexpensive portable scanners capable of analyzing leaf/tissue samples and matching the DNA barcode with database information, the field of botanical phylogenetics and research will benefit greatly especially since plant identification and classification will be available to more than a few experts. In addition, such identification and classification will be more accurate than that provided by sole reliance on visual examination and physical morphology (especially with regard to cryptic species) while endangered species will be able to be easily tracked and better protected, and people will have greater assurance pertaining to the food, drinks, and/or medicine they consume.
Friday, June 25, 2010
Crick's Central Dogma of Molecular Biology - DNA to RNA to Protein
The idea that each organism possesses a unique genetic code which is passed to future generations was hypothesised long before the actual mechanisms, or indeed the source, of such inheritable information was agreed. After Mendel (1857) demonstrated that phenotypic characteristics could be transferred from parent to offspring, Fred Griffith set out in 1928 to find evidence that the molecule responsible for preserving and transmitting this information was DNA. This was later confirmed conclusively by experiments conducted by Avery and (later) by Hershey & Chase, establishing that DNA was indeed the arsenal of heritable information. From this affirmation and the knowledge that RNA was the immediate precursor for protein, Francis Crick proposed in a 1954 paper - and reasserted in 1970 - formulated a flow diagram which has become known as the central dogma of molecular biology: DNA to RNA to Protein.
The central dogma is essentially a framework that outlines the transfer of sequential information from storage as DNA to the expression of that information as a functional entity as protein. Most importantly, it dictates that information can only flow from nucleic acid to protein, and not from protein to nucleic acid i.e. that "once (sequential) information has passed into protein it cannot get out again (F.H.C. Crick, 1958). At the time of print, all evidence suggested that this transfer or flow of information occurred linearly, however modern advances in molecular biology and genetics have shown that this idea was too simple.
The interrelationship between these three important molecules may be more complex than once thought, however the essential concept still holds true. All organisms (with the exception of some viruses, which use RNA) use DNA as a storage facility for their genetic information. This information, which in reality is triplet base pair codons, is then used a template to be faithfully transcribed to an intermediate RNA. Once transcription is complete, it can then be translated in the ribosome to a corresponding amino acid sequence that codes for the assembly of a functional protein. The dogma infers that it is DNA that directs the development of the organism and that protein formation ultimately relies on the DNA sequence. Additionally, the concept is also important in that it stresses that the information contained within DNA must first depend on RNA for transport. Significantly, it focuses on protein as the product of gene expression, an idea that is now well understood due to successful mapping of the genome.
Modern discoveries have highlighted that the flow of genetic information is much more dynamic. For example, some RNA does not code for protein and instead is destined to remain as an RNA nucleotide. This type of RNA is known as functional or ncRNA - i.e. non-coding - such as tRNA and rRNA. Additionally, ribozymes can act as catalysts, performing their own 'protein' functions without ever completed the sequential route all the way to protein. Another modern extension of the dogma is that RNA can also act as a template for DNA synthesis. This process is known as reverse transcription which uses the enzyme reverse transcriptase and has been demonstrated to exist in retroviruses. These findings are important for the development of the theory as it confirms Crick's postulations that RNA could go back to DNA and further extends our understanding of the central concept.
The importance of the central dogma as a concept is perhaps best illustrated, somewhat paradoxically, by the one discovery which directly challenges it. In his original assertions, Crick explicitly stated that 'transfer from protein to protein' was impossible. It is now widely accepted that infectious proteins known as prions, previously thought to be viral in nature, are built directly from protein by triggering abnormal synthesis from its native form. This initially sparked a myriad of papers postulating counter theories, based on the assumption that protein self replication violated the central dogma. It is clear from such actions that the central dogma has core significance that has developed way beyond the actual statements in Crick's original paper. Scientific discovery in every field is fueled by the desire to find simple, underlying theories that can explain the many complexities of their endeavors in an uncomplicated theoretical framework. We know that DNA is the root of our heritable information and we know that the functional units that make life possible are proteins. Despite requiring some adjustment to the finer detail Crick's version of the central dogma certainly laid such a foundation, giving biologists a central concept to both orientate from and build around.
The central dogma is essentially a framework that outlines the transfer of sequential information from storage as DNA to the expression of that information as a functional entity as protein. Most importantly, it dictates that information can only flow from nucleic acid to protein, and not from protein to nucleic acid i.e. that "once (sequential) information has passed into protein it cannot get out again (F.H.C. Crick, 1958). At the time of print, all evidence suggested that this transfer or flow of information occurred linearly, however modern advances in molecular biology and genetics have shown that this idea was too simple.
The interrelationship between these three important molecules may be more complex than once thought, however the essential concept still holds true. All organisms (with the exception of some viruses, which use RNA) use DNA as a storage facility for their genetic information. This information, which in reality is triplet base pair codons, is then used a template to be faithfully transcribed to an intermediate RNA. Once transcription is complete, it can then be translated in the ribosome to a corresponding amino acid sequence that codes for the assembly of a functional protein. The dogma infers that it is DNA that directs the development of the organism and that protein formation ultimately relies on the DNA sequence. Additionally, the concept is also important in that it stresses that the information contained within DNA must first depend on RNA for transport. Significantly, it focuses on protein as the product of gene expression, an idea that is now well understood due to successful mapping of the genome.
Modern discoveries have highlighted that the flow of genetic information is much more dynamic. For example, some RNA does not code for protein and instead is destined to remain as an RNA nucleotide. This type of RNA is known as functional or ncRNA - i.e. non-coding - such as tRNA and rRNA. Additionally, ribozymes can act as catalysts, performing their own 'protein' functions without ever completed the sequential route all the way to protein. Another modern extension of the dogma is that RNA can also act as a template for DNA synthesis. This process is known as reverse transcription which uses the enzyme reverse transcriptase and has been demonstrated to exist in retroviruses. These findings are important for the development of the theory as it confirms Crick's postulations that RNA could go back to DNA and further extends our understanding of the central concept.
The importance of the central dogma as a concept is perhaps best illustrated, somewhat paradoxically, by the one discovery which directly challenges it. In his original assertions, Crick explicitly stated that 'transfer from protein to protein' was impossible. It is now widely accepted that infectious proteins known as prions, previously thought to be viral in nature, are built directly from protein by triggering abnormal synthesis from its native form. This initially sparked a myriad of papers postulating counter theories, based on the assumption that protein self replication violated the central dogma. It is clear from such actions that the central dogma has core significance that has developed way beyond the actual statements in Crick's original paper. Scientific discovery in every field is fueled by the desire to find simple, underlying theories that can explain the many complexities of their endeavors in an uncomplicated theoretical framework. We know that DNA is the root of our heritable information and we know that the functional units that make life possible are proteins. Despite requiring some adjustment to the finer detail Crick's version of the central dogma certainly laid such a foundation, giving biologists a central concept to both orientate from and build around.
OctoClean Janitorial Franchise
Every company has to start somewhere, and for OctoClean that somewhere was in Riverside, California as an employee-run cleaning service company called Service Pros. Over the last twenty years, Service Pros has developed into a strong contender in the cleaning business, changing its name to OctoClean in 2000 upon expanding into a franchising company. Today there are more than 150 unit franchisees bringing in almost $4 million in revenue each year.
These unit franchises offer those interesting in becoming business owners the safety, backing, and support of a large company while maintaining a certain amount of freedom. In order to both establish and sustain a unit franchise, OctoClean provides their franchisees with a multitude of resources including customer service assistance, financial assistance, and continuous training.
OctoClean also utilizes a network of master franchises in order to uphold a high level of support and security for their unit franchise owners. Master franchisees become the CEO of their own company that includes multiple unit franchises inside an exclusive territory. This arrangement is great for those looking to exercise and grow their own organizational, sales, economic, and business management skills.
OctoClean's mission statement makes it clear that they want their level of success to be available and accessible to everyone: "OctoClean is an enterprise whose purpose is to transform the janitorial industry. We empower and enable people to be successful business owners. We create programs and services that thrill our customers. Our mission is to have the rewards and freedom of successful franchise ownership available to all people." Having such a strong message at the core of a company says a lot about where you've come from and where you're going as a business.
As they continue to spread across the west, the Southern California company OctoClean climbs its way to the top of the janitorial franchise industry. From its humble beginnings as a small employee run business twenty years ago to its multi-million dollar success as a franchising company, OctoClean persists as a true competitor in the cleaning business.
These unit franchises offer those interesting in becoming business owners the safety, backing, and support of a large company while maintaining a certain amount of freedom. In order to both establish and sustain a unit franchise, OctoClean provides their franchisees with a multitude of resources including customer service assistance, financial assistance, and continuous training.
OctoClean also utilizes a network of master franchises in order to uphold a high level of support and security for their unit franchise owners. Master franchisees become the CEO of their own company that includes multiple unit franchises inside an exclusive territory. This arrangement is great for those looking to exercise and grow their own organizational, sales, economic, and business management skills.
OctoClean's mission statement makes it clear that they want their level of success to be available and accessible to everyone: "OctoClean is an enterprise whose purpose is to transform the janitorial industry. We empower and enable people to be successful business owners. We create programs and services that thrill our customers. Our mission is to have the rewards and freedom of successful franchise ownership available to all people." Having such a strong message at the core of a company says a lot about where you've come from and where you're going as a business.
As they continue to spread across the west, the Southern California company OctoClean climbs its way to the top of the janitorial franchise industry. From its humble beginnings as a small employee run business twenty years ago to its multi-million dollar success as a franchising company, OctoClean persists as a true competitor in the cleaning business.
Monday, April 12, 2010
Nucleic acid
A nucleic acid is a macromolecule composed of chains of monomeric nucleotides. In biochemistry these molecules carry genetic information or form structures within cells. The most common nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Nucleic acids are universal in living things, as they are found in all cells and viruses. Nucleic acids were first discovered by Friedrich Miescher in 1871.
Artificial nucleic acids include peptide nucleic acid (PNA), Morpholino and locked nucleic acid (LNA), as well as glycol nucleic acid (GNA) and threose nucleic acid (TNA). Each of these is distinguished from naturally-occurring DNA or RNA by changes to the backbone of the molecule.The term "nucleic acid" is the generic name for a family of biopolymers, named for their role in the cell nucleus. It was later discovered that some nucleic acids are exclusive of the mitochondrion (e.g. Mitochondrial DNA). The monomers from which nucleic acids are constructed are called nucleotides. Nucleic acids are linear, unbranched polymers of nucleotides.
Each nucleotide consists of three components: a nitrogenous heterocyclic base, which is either a purine or a pyrimidine; a pentose sugar; and a phosphate group. Nucleic acid types differ in the structure of the sugar in their nucleotides - DNA contains 2-deoxyribose while RNA contains ribose (where the only difference is the presence of a hydroxyl group). Also, the nitrogenous bases found in the two nucleic acid types are different: adenine, cytosine, and guanine are found in both RNA and DNA, while thymine only occurs in DNA and uracil only occurs in RNA. Other rare nucleic acid bases can occur, for example inosine in strands of mature transfer RNA.
Nucleic acids are usually either single-stranded or double-stranded, though structures with three or more strands can form. A double-stranded nucleic acid consists of two single-stranded nucleic acids held together by hydrogen bonds, such as in the DNA double helix. In contrast, RNA is usually single-stranded, but any given strand may fold back upon itself to form secondary structure as in tRNA and rRNA. Within cells, DNA is usually double-stranded, though some viruses have single-stranded DNA as their genome. Retroviruses have single-stranded RNA as their genome.
The sugars and phosphates in nucleic acids are connected to each other in an alternating chain, linked by shared oxygens, forming a phosphodiester bond. In conventional nomenclature, the carbons to which the phosphate groups attach are the 3' end and the 5' end carbons of the sugar. This gives nucleic acids polarity. The bases extend from a glycosidic linkage to the 1' carbon of the pentose sugar ring. Bases are joined through N-1 of pyrimidines and N-9 of purines to 1' carbon of ribose through N-β glycosyl bond.Ribonucleic acid, or RNA, is a nucleic acid polymer consisting of nucleotide monomers, which plays several important roles in the processes of transcribing genetic information from deoxyribonucleic acid (DNA) into proteins. RNA acts as a messenger between DNA and the protein synthesis complexes known as ribosomes, forms vital portions of ribosomes, and serves as an essential carrier molecule for amino acids to be used in protein synthesis. The three types of RNA include tRNA (transfer), mRNA (messenger) and rRNA (ribosomal).
Artificial nucleic acids include peptide nucleic acid (PNA), Morpholino and locked nucleic acid (LNA), as well as glycol nucleic acid (GNA) and threose nucleic acid (TNA). Each of these is distinguished from naturally-occurring DNA or RNA by changes to the backbone of the molecule.The term "nucleic acid" is the generic name for a family of biopolymers, named for their role in the cell nucleus. It was later discovered that some nucleic acids are exclusive of the mitochondrion (e.g. Mitochondrial DNA). The monomers from which nucleic acids are constructed are called nucleotides. Nucleic acids are linear, unbranched polymers of nucleotides.
Each nucleotide consists of three components: a nitrogenous heterocyclic base, which is either a purine or a pyrimidine; a pentose sugar; and a phosphate group. Nucleic acid types differ in the structure of the sugar in their nucleotides - DNA contains 2-deoxyribose while RNA contains ribose (where the only difference is the presence of a hydroxyl group). Also, the nitrogenous bases found in the two nucleic acid types are different: adenine, cytosine, and guanine are found in both RNA and DNA, while thymine only occurs in DNA and uracil only occurs in RNA. Other rare nucleic acid bases can occur, for example inosine in strands of mature transfer RNA.
Nucleic acids are usually either single-stranded or double-stranded, though structures with three or more strands can form. A double-stranded nucleic acid consists of two single-stranded nucleic acids held together by hydrogen bonds, such as in the DNA double helix. In contrast, RNA is usually single-stranded, but any given strand may fold back upon itself to form secondary structure as in tRNA and rRNA. Within cells, DNA is usually double-stranded, though some viruses have single-stranded DNA as their genome. Retroviruses have single-stranded RNA as their genome.
The sugars and phosphates in nucleic acids are connected to each other in an alternating chain, linked by shared oxygens, forming a phosphodiester bond. In conventional nomenclature, the carbons to which the phosphate groups attach are the 3' end and the 5' end carbons of the sugar. This gives nucleic acids polarity. The bases extend from a glycosidic linkage to the 1' carbon of the pentose sugar ring. Bases are joined through N-1 of pyrimidines and N-9 of purines to 1' carbon of ribose through N-β glycosyl bond.Ribonucleic acid, or RNA, is a nucleic acid polymer consisting of nucleotide monomers, which plays several important roles in the processes of transcribing genetic information from deoxyribonucleic acid (DNA) into proteins. RNA acts as a messenger between DNA and the protein synthesis complexes known as ribosomes, forms vital portions of ribosomes, and serves as an essential carrier molecule for amino acids to be used in protein synthesis. The three types of RNA include tRNA (transfer), mRNA (messenger) and rRNA (ribosomal).
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