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| Subject keyword(s) | Astronomy, Biochemistry, Biology, Cell, Cellular structures, DNA, Double helix, Earth science, Genetics, Geoscience, Life Science, Life science, Nucleic acids, Nucleotide bases, Nucleus, Phosphate molecules, Science, Space Science, Space sciences, Watson |
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| Intended audience | Educator, Learner |
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| Resource format | text, text/html |
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Register | Log In Library MyClassroom About Us Help Library > Biology > Nucleic Acids Module Questions & Quizzes Links en español print Nucleic Acids DNA and RNA by Anthony Carpi, Ph.D. Living organisms are complex systems. Hundreds of thousands of proteins exist inside each one of us to help carry out our daily functions (see our Fats and Proteins module for more information). These proteins are produced locally, assembled piece-by-piece to exact specifications. An enormous amount of information is required to manage this complex system correctly. This information, detailing the specific structure of the proteins inside of our bodies, is stored in a set of molecules called nucleic acids. The nucleic acids are very large molecules that have two main parts. The backbone of a nucleic acid is made of alternating sugar and phosphate molecules bonded together in a long chain, represented below: sugar phosphate sugar phosphate ... Each of the sugar groups in the backbone is attached (via the bond shown in red) to a third type of molecule called a nucleotide base: nucleotide base nucleotide base | | sugar phosphate sugar phosphate ... Though only four different nucleotide bases can occur in a nucleic acid, each nucleic acid contains millions of bases bonded to it. The order in which these nucleotide bases appear in the nucleic acid is the coding for the information carried in the molecule. In other words, the nucleotide bases serve as a sort of genetic alphabet on which the structure of each protein in our bodies is encoded. DNA In most living organisms (except for viruses), genetic information is stored in the molecule deoxyribonucleic acid, or DNA. DNA is made and resides in the nucleus of living cells. DNA gets its name from the sugar molecule contained in its backbone(deoxyribose); however, it gets its significance from its unique structure. Four different nucleotide bases occur in DNA: adenine (A), cytosine (C), guanine (G), and thymine (T). Chemical Structure of the DNA Nucleotides These nucleotides bind to the sugar backbone of the molecule as follows:� A T G C sugar phosphate sugar phosphate sugar phosphate sugar ... The versatility of DNA comes from the fact that the molecule is actually double-stranded. The nucleotide bases of the DNA molecule form complementary pairs: The nucleotides hydrogen bond to another nucleotide base in a strand of DNA opposite to theoriginal. This bonding is specific, and adenine always bonds to thymine (and vice versa) and guanine always bonds to cytosine (and vice versa). This bonding occurs across the molecule, leading to a double-stranded system as pictured below: sugar phosphate sugar phosphate sugar phosphate sugar ... T A C G � � � � A T G C sugar phosphate sugar phosphate sugar phosphate sugar ... In the early 1950s, four scientists, James Watson and Francis Crick at Cambridge University and Maurice Wilkins and Rosalind Franklin at King's College, determined the true structure of DNA from data and X-ray pictures of the molecule that Franklin had taken. In 1953, Watson and Crick published a paper in the scientific journal Nature describing this research. Watson, Crick, Wilkins and Franklin had shown that not only is the DNA molecule double-stranded, but the two strands wrap around each other forming a coil, or helix. The true structure of the DNA molecule is a double helix, as shown at right. The double-stranded DNA molecule has the unique ability that it can make exact copies of itself, or self-replicate. When more DNA is required by an organism (such as during reproduction or cell growth) the hydrogen bonds between the nucleotide bases break and the two single strands of DNA separate. New complementary bases are brought in by the cell and paired up with each of the two separate strands, thus forming two new, identical, double-stranded DNA molecules. This concept is illustrated in the animation below. The Replication of DNA Concept simulation - Reenacts replication of DNA. (Flash required) RNA Ribonucleic acid, or RNA, gets its name from the sugar group in the molecule's backbone - ribose. Several important similarities and differences exist between RNA and DNA. Like DNA, RNA has a sugar-phosphate backbone with nucleotide bases attached to it. Like DNA, RNA contains the bases adenine (A), cytosine (C), and guanine (G); however, RNA does not contain thymine, instead, RNA's fourth nucleotide is the base uracil (U). Unlike the double-stranded DNA molecule, RNA is a single-stranded molecule. RNA is the main genetic material used in the organisms called viruses, and RNA is also important in the production of proteins in other living organisms. RNA can move around the cells of living organisms and thus serves as a sort of genetic messenger, relaying the information stored in the cell's DNA out from the nucleus to other parts of the cell where it is used to help make proteins. A U G C sugar phosphate sugar phosphate sugar phosphate sugar ... RNA External Resources The Double Helix: A Personal Account of the Discovery of the Structure of DNA Rosalind Franklin: The Dark Lady of DNA Other Recommended Products Back to top Anthony Carpi, Ph.D. "Nucleic Acids: DNA and RNA," Visionlearning Vol. BIO-1 (1), 2003. http://www.visionlearning.com/library/module_viewer.php?mid=63 Visionlearning Resources Glossary Library Biology AdaptationCellsCharles Darwin ICharles Darwin IICharles Darwin IIIDNA IDNA IIDNA IIIGenetics IGenetics IITaxonomy ITaxonomy II: Nomenclature Chemistry Acids and BasesAtomic Theory IAtomic Theory IICarbohydratesChemical BondingChemical EquationsChemical ReactionsFats and ProteinsMatterMatter: States of MatterNuclear ChemistryOrganic ChemistryThe MoleThe Periodic Table of ElementsWater Earth Science Earth StructureEarth's AtmosphereMinerals IMinerals IIMinerals IIIPlate Tectonics IPlate Tectonics IIThe Carbon CycleThe Hydrologic CycleThe Nitrogen CycleThe Rock Cycle General Science DensityEnergyTemperatureThe Metric SystemThe Scientific MethodUnit Conversion Physics GravityLight ILight IIWaves and Wave Motion Process of Science Data: Analysis and InterpretationData: StatisticsData: Uncertainty, Error, and ConfidenceData: Using Graphs and Visual DataIdeas in Science: Scientific ControversyIdeas in Science: Theories, Hypotheses, and LawsResearch Methods: ComparisonResearch Methods: DescriptionResearch Methods: ExperimentationResearch Methods: ModelingResearch Methods: The Practice of ScienceScientific Communication: Peer ReviewScientific Communication: The How and Why of Scientific MeetingsScientific Communication: Understanding Scientific Journals and ArticlesScientific Communication: Utilizing the Scientific LiteratureScientific EthicsScientific Institutions and SocietiesScientists and the Scientific CommunityThe Nature of Scientific KnowledgeThe Process of Science Scientific Research Bone Changes in Rock ClimbersClassic Experiment: Meselson and StahlCreativity in ScienceFrom Stable Chromosomes to Jumping GenesStudying Climate Change with Kevin ArrigoThe Case of the Ivory-billed Woodpecker Toxicology & Pharmacology Absorption, Distribution and Storage of Chemicals Trigonometry Wave Mathematics Interactive Animations Bohr's Atom: Quantum Behavior in HydrogenThe reaction of sodium with chlorineAn example of an interactive learning tool: Mid-Ocean RidgesLeaning Tower of Pisa ExperimentThe formation of waterThe Virtual Animal CellNuclear FusionTwo Types of Nuclear Chain ReactionsDalton's PlayhouseDarwin's FinchesThe Illustrated Animal CellStates of MatterThe Illustrated Periodic Table External Resources The Double Helix: A Personal Account of the Discovery of the Structure of DNA Rosalind Franklin: The Dark Lady of DNA Other Recommended Products Quotes I was shown Rosalind Franklin's X-ray photograph and "Whooo! That was a helix!", and a month later, we had the structure... -James Watson, 1928- �The capacity to blunder slightly is the real marvel of DNA. Without this special attribute, we would still be anaerobic bacteria and there would be no music.� - Lewis Thomas The Process of Science Want ad-free content? Register here. Support for Visionlearning has been provided by: Copyright © 2003 - 2012, Visionlearning, Inc.