The lower the twist angle, the higher the number of base pairs per turn. Building Blocks of Nucleic Acids 1. Figure \(\PageIndex{19}\) shows the Watson Crick and first set of alternative non-canonical base pairs. Google Scholar. Before this information can be used for protein synthesis, however, an RNA copy (transcript) of the gene must first be made. The structure of RNA has evolved to serve those added functions. It is forme by the deamination of adenosine by the enzyme adenosine deaminase. The peptide is shown in cyan and its arginine side chains are shown as cyan lines. Phosphate Group 3. Crick, Wilkins, and Watson each received one third of the 1962 Nobel Prize in Physiology or Medicine for their contributions to the discovery. Guerrini, L. and Alvarez-Puebla, R.A. Nanomaterials 2021, 11, 326. https://doi.org/10.3390/nano11020326. Direct link to tyersome's post Within a gene *usually* o, Posted 7 years ago. Nucleic acids are categorised into two different forms, DNA, i.e., Deoxyribonucleic Acid and RNA, i.e., Ribonucleic Acid. This process of transmission is called heredity. Such a domain called a nucleotide-binding fold, is found in many enzymes that bind ATP and nucleotide cofactors. The most common nucleic acids in nature are DNA and RNA. Biological Functions of Nucleic Acids - unacademy.com If the binding of the third strand in the major groove occurs at site where RNA polymerase binds to a gene, then third stand can inhibit gene transcription. DNA reserves genetic information and is responsible for maintaining the identity of species over the centuries. Figure \(\PageIndex{27}\): parallel quadruplexes from human telomeric DNA (1KF1). The knot consists of a hairpin in the nucleic acid structure with the loop between the helices paired to another part of the nucleic acid. These can be formed in DNA and RNA from G-rich sequences involving tetrads of guanine bases that are hydrogen bonded. The primary act of nucleic acid is to store information. Prokaryotic Chromosomes (2017) In MediaWiki, Available at: https://www.wikilectures.eu/w/Prokaryotic_Chromosomes, Wikipedia contributors. Carbohydrates, lipids, proteins and nucleic acids are the 4 major classes of biological macromolecules that are necessary for life and survival. Adenosine 5'-ATP, triphosphate, is by far the most widely used for this purpose, but in some reactions, UTP, GTP, and CTP are also used. (2019, July 19). Nucleic Acids - Structure and Function - ThoughtCo Also, AT/GC are found in DNA while RNA is made from AU/GC. New insights gained from recent studies suggest that nucleic acids not only code genetic information in sequences but also have unknown functions regarding their structures and stabilities through drastic structural changes in cellular . The excess stability of dsDNA enriched in GC base pairs can still be explained by the extra stabilization for an additional hydrogen bond per GC base pair. Some Nucleotides Are Regulatory Molecules. Under standard conditions, hydrolysis of the ester bond yields about 14 kJ / mol, whereas hydrolysis of each bond yields about 30 kJ / mol. (b) Matove B-DNA with nearly 11 base pairs within one helical turn. Other Functions of Nucleic Acid Nucleotides Carry Chemical Energy in Cells One or two additional phosphates may be attached to the phosphate group covalently linked to a ribonucleotide's 5' hydroxyl. RNA uses the same nitrogenous bases as DNA, except for Thymine. Biological Functions of Nucleic Acids - DNA and RNA. Hydrolysis of Pi-Pi 2Pi has a G = -7 kcal/mol (-29 kJ/mol) and is essential to provide the overall negative G (-6.5 kcal/mol, 27 kJ/mol) of the DNA synthesis reaction. Learn about nucleic acids, biological functions of Nucleic Acids, and topics related to them. Hover over the guanine bases in one layer and you will find that one layer consists of guanines 4, 10, 16 and 22, which derive from the last G in each of the repeats in the sequence of the oligomer used (5'-AGGGTTAGGGTTAGGGTTAGGG-3'). Nucleic acids are found in every living thing plants, animals, bacteria, viruses, fungi that uses and converts energy. Legal. The triplet base pair are antiparallel to each other. The tRNA that binds, and thus the amino acid that's added, at a given moment is determined by the sequence of the mRNA that is being "read" at that time. Only two nucleic acids are believed to exist in nature: DNA and RNA, or ribonucleic acid. A nucleic acid is a chain of nucleotides which stores genetic information in biological systems. To log in and use all the features of Khan Academy, please enable JavaScript in your browser. Direct link to StephYakir87's post The first part is true, T, Posted 7 years ago. The answer is a definite no. If there are only four base pairs of RNA and DNA, then why do we list five? Every living thing on Earth uses nucleic acids as a source or location for storing information of source code or hereditary information. Sugimoto, K., Sugisaki, H., Okamoto, T., Takanami, M. (1975) Nucl. Biologydictionary.net, September 07, 2017. https://biologydictionary.net/nucleic-acid/. Larger propeller angles are associated with increased rigidity. Nucleotides are building blocks of nucleic acids (DNA and RNA).A nucleic acid contains a chain of nucleotides linked together with covalent bonds to form a sugar-phosphate backbone with protruding nitrogenous bases. DNA is the genetic material found in all living organisms, ranging from single-celled bacteria to multicellular mammals. 6.2: What Are Lipids? - Medicine LibreTexts In that process the homologous DNA strand but exchange with a paired homolog. Adapted from Calladine and Drews schematic box representation. Nucleic acid is a natural chemical compound that can be broken down to produce phosphoric acid, sugars and a combination of organic bases (nucleotide, purines, and pyrimidines). Although this requirement for adenosine has not been investigated in detail, it must involve the binding energy between enzyme and substrate (or cofactor) that is used both in catalysis and in stabilizing the initial enzyme-substrate complex. How do mRNA and tRNA communicate with eachother during the formation of the proteins? Dickson, R.C., Abelson, J., Barnes, W.M., Reznikoff, W.S. We also learn the importance of XeF6 molecular geometry and bond angles importance and much more about the topic in detail. How Nucleic Acids Work They are the cell's main information-carrying molecules and they ultimately determine the inherited traits of every living organism by guiding the entire process of protein synthesis. Quadruplex can be forme in 1 strand of a nucleic acid (as in the above model) or from 2 or 4 separate strands. The general principles of recognition of nucleic acids by proteins are among the most exciting problems of molecular biology. They write new content and verify and edit content received from contributors. Get subscription and access unlimited live and recorded courses from Indias best educators. "Nucleic Acid. You would be in general correct in this belief, but you'd be missing the more important contributor to ds-DNA stability, base () stacking and the noncovalent interactions associated with the stacking. DNA is the chemical basis of heredity and may be regarded as the reserve of genetic information. Pseudoknots can be found in mRNA and in ribosomal RNA and affect the translation of the RNA (decoding to instruct the synthesis of a protein sequence). The major function of nucleic acids is to store the genetic code of living organisms. DNA and RNA are both important information-carrying molecules, although their . Human genome. Click the image for a popup or use the external links in column 1. Figure \(\PageIndex{30}\) shows an interactive iCn3D model of a solution conformation of a parallel DNA triple helix (1BWG). Composed of fats and oils, lipids are molecules that yield high energy and have a chemical composition mainly of carbon, hydrogen, and oxygen. Before understanding the biological function of nucleic acids, we need to understand the term Nucleic Acid first. The main differences between the two is that, while DNA includes the bases A, C, G and T, RNA includes A, C, G and U. Detection of Triple Helical Nucleic Acids with Vibrational Circular (Assuming that you are refering to DNA and RNA) DNA is really important for cell division (which is important for growth, development, and regeneration) and stores genetic information. Furthermore, slide or flip effects can also modify the geometrical orientation of the helix. Review of 4 major types of biomolecules and their functions. The structure contains a single DNA strand (5'-AGGGTTAGGGTTAGGGTTAGGG-3') which contains four TTAGGG repeats. Triple helices can form when single stranded DNA formed during replication, transcription or DNA repair with half of the required mirror symmetry folds back into the adjacent major grove and base pairs using Hoogsteen/reverse Hoogsteen bonding, which can be stabilized by Mg2+. During normal cell metabolism, RNA is constantly being made and broken down. The well-known structure of the DNA double helix allows this information to be copied and passed on to the next generation. The two rings in purines are synthesized while attached to the ribose phosphate during the assembly of adenine or guanine nucleosides. The hydrogen bond interaction energy is hence more favorable in the stack. KOBAS-i: intelligent prioritization and exploratory visualization of RNA is single stranded but may adopt many secondary and tertiary conformations not unlike that of a protein. From Chargaffs rules, the two strands will pair A with T and G with C. This pairs a keto base with an amino base, a purine with a pyrimidine. Basics of Biomolecules Carbon is the central atom Carbon will bond covalently because of 4 valence electrons Carbon likes to share electrons with sulfur, phosphorous, oxygen, nitrogen, other. Unacademy is Indias largest online learning platform. If you examine the iCn3D models of nucleic acids presented above, you will see the the base pairs are not perfectly flat but are twisted. Nucleotides Carry Chemical Energy in Cells, One or two additional phosphates may be attached to the phosphate group covalently linked to a ribonucleotide's 5' hydroxyl. The phosphate group connects successive sugar residues by bridging the 5-hydroxyl group on one sugar to the 3-hydroxyl group of the next sugar in the chain. 2023 Leaf Group Ltd. / Leaf Group Media, All Rights Reserved. John's University and Western Oregon University, Additional Alternative Structures: Quadruplexes and Triple Helices, https://commons.wikimedia.org/wiki/FDNA_RNA-EN.svg, https://en.Wikipedia.org/wiki/File:D_structure.svg, https://en.Wikipedia.org/wiki/Nucleic_acid_sequence, Creative Commons Attribution-ShareAlike License, https://structure.ncbi.nlm.nih.gov/ib5HUbmuQrCobg8, https://structure.ncbi.nlm.nih.gov/i8C7qBqgh8ZTJH9, https://structure.ncbi.nlm.nih.gov/iZtdeJqQXvjCKfA, https://structure.ncbi.nlm.nih.gov/icn3d/share.html?WQWkYi1FrM4DSY2i7, https://structure.ncbi.nlm.nih.gov/i5kLYSSfG7rsmS9, https://en.Wikipedia.org/wiki/File:A_and_Z-DNA.png, Lenglet and David-Cordonnier (2010) Journal of Nucleic Acids, http://dx.doi.org/10.4061/2010/290935, ://x3dna.org/highlights/schematiair-parameters, https://structure.ncbi.nlm.nih.gov/iT8CJ3pCe986Vx9, https://structure.ncbi.nlm.nih.gov/iLtwfzyeqDCaPEA, https://structure.ncbi.nlm.nih.gov/ireyeD6JQM1djq6, https://doi.org/10.1038/s41467-018-03221-z, http://creativecommons.org/licenses/by/4.0/, https://doi.org/10.1038/s41467-018-03516-1Creative, https://structure.ncbi.nlm.nih.gov/iSLLRv1m8HQXKcA, https://structure.ncbi.nlm.nih.gov/iy5joFHDgWJQsQ6, https://creativecommons.org/licenses/by/4.0/, https://structure.ncbi.nlm.nih.gov/i5JU813eNjND8E7, http://creativecommons.org/licenses/by-nc/4.0/, https://commons.wikimedia.org/wiki/Fomosome_en.svg, https://www.researchgate.net/publication/303846502_Metal_ion_induced_heterogeneity_in_RNA_folding_studied_by_smFRET, https://bio.libretexts.org/Bookshelves/Genetics/Book%3A_Working_with_Molecular_Genetics_(Hardison)/Unit_I%3A_Genes%2C_Nucleic_Acids%2C_Genomes_and_Chromosomes/2%3A_Structures_of_Nucleic_Acids/2.5%3A_B-Form%2C_A-Form%2C_and_Z-Form_of_DNA, https://www.hindawi.com/journals/jna/2010/290935/, https://www.mechanobio.info/genome-regulation/what-are-chromosomes-and-chromosome-territories/, https://www.genome.gov/human-genome-project, https://en.Wikipedia.org/w/index.php?title=DNA&oldid=905364161, https://www.wikilectures.eu/w/Prokaryotic_Chromosomes, avatar@https://bio.libretexts.org/@api/deki/files/67680/Patty_Flatt.jpg, status page at https://status.libretexts.org. Direct link to kind of blue's post How do mRNA and tRNA comm, Posted 7 years ago. Image of a ribosome (made of proteins and rRNA) bound to an mRNA, with tRNAs bringing amino acids to be added to the growing chain. Note that when looking from the top view, down on a DNA base pair, that the position where the base pairs attach to the DNA backbone is not equidistant, but that attachment favors one side over the other. Please refer to our Nucleic Acid Structure article for more information. 1. The nucleic acids are vital biopolymers found in all living things, where they function to encode, transfer, and express genes. W. A. Benjamin, Inc., New York, 1976. Vikrant Kumar Sinha - Postdoctoral Researcher - LinkedIn (ii) Nucleic acids (both DNA and RNA) are responsible for protein synthesis in a cell. Nucleic Acids- Nucleosides and Nucleotides - Microbe Notes Biological functions of Nucleic Acids - slideshare.net By far the most important function of nucleic acids for living things is their role as carriers of information. A more detailed description of polymerase reaction mechanisms will be covered in Chapters X and Y, covering DNA Replication and Repair, and DNA Transcription. https://www.khanacademy.org/science/organic-chemistry/aromatic-compounds/aromatic-stability/v/aromatic-heterocycles-i, https://en.wikipedia.org/wiki/Heterocyclic_compound, https://en.wikipedia.org/wiki/Abiogenesis, https://en.wikipedia.org/wiki/Nucleic_acid_analogues, https://www.sciencedaily.com/terms/rna.htm, Involved in protein synthesis and gene regulation; carrier of genetic information in some viruses. The tRNA carries an amino acid, our ingredient to make the protein. Direct link to Katherine's post Why do some nitrogenous b, Posted 6 years ago. There are two purposes in the genetic information stored in the DNA nucleotide sequence. The phosphate groups serve as links between the sugars in each strand of DNA. Nitrogenous Base Types of Nucleotide Bases 1. 4. Nucleic acids can be defined as organic molecules present in living cells. 2023 Springer Nature Switzerland AG. 2008. doi: 10.1016/j.biochi.2008.02.011. Nucleic acids are naturally occurring chemical compounds that serve as the primary information-carrying molecules in cells. Lab. Longitudinal helical extensions might be important when homologous gene recombine. Biology, 21.06.2019 20:40. The same DNA without bound protein has no Hoogsteen base pairs. Figure \(\PageIndex{1}\) shows a low resolution comparison of the structure of DNA and RNA. The third type of double helix formed is a left-handed helical structure known as the Z-form, or Z-DNA. The structure contains many GU wobble base pairs as well as two CU base pairs between two pyrimidine bases. Thus, DNA is directional and is always synthesized in the 5 to 3 direction. Adenine Nucleotides are Components of many Enzyme Cofactors. Biological functions of Nucleic Acids Aiswarya Surendran Follow B.Ed physical science at KUCTE, Kumarapuram, TVPM at Student Advertisement Recommended Structure and Function of Nucleic Acids cgales 17k views 15 slides Nucleic Acid / Protein structure & Functions RGCL 12k views 20 slides Structure of nucleic acid Dr Muhammad Mustansar 1.4k views Direct link to Greacus's post If A-T bonds have 2 hydro, Posted 6 years ago. So, in a chain of DNA or RNA, each nucleotide has just one phosphate group. Read More: How do you use gel permeation chromatography? The two main classes of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA and RNA structure and function. What are the biological functions of nucleic acids? - Quora Nucleic acids are long chainlike molecules composed of a series of nearly identical building blocks callednucleotides. The double stranded canonical helix (D1D2) consist of 31 base pairs in which strand D1 is pyrimidine rich and D2 is purine-rich strand (D2). Inosine, a variant of the base adenine, can be found in RNA. Many other cytoplasmic RNA molecules (ribosomal RNAs; rRNAs) have major structural roles in which they contribute to the formation and function of ribosomes (organellar protein synthesis machinery) or serve as adapter molecules (transfer RNAs; tRNAs) for translating RNA information into specific polymerized amino acid sequences. The term polymer comes from poly for many and mer for parts, referring to the fact that each nucleic acid is made of many nucleotides. After looking at the myriad of structures showing the nearly parallel hydrogen bonded base pairs, and from ideas from most textbooks and classes you have taken, you probably think that double-stranded DNA is held together and stabilized by hydrogen bonds between the bases. In Wikipedia, The Free Encyclopedia. The solitary A68 base is shown projecting away from the RNA. An additional phosphate group from ATP is then added by another kinase to form a deoxyribonucleoside triphosphate, the immediate precursor of DNA. The two strands are held together by H-bonding between the complementary base pairs (A pairs with T and G pairs with C) as shown in Figure \(\PageIndex{10}\) below. For instance, if you know that the sequence of one strand is 5-AATTGGCC-3, the complementary strand must have the sequence 3-TTAACCGG-5. Nucleic acids are large biomolecules that play essential roles in all cells and viruses. Uracil (Pyrimidines) Importance of Nucleotides References What Is A Nucleotide? Nucleic acids are molecules that store and transmit hereditary information and energy in living things. The six-atom pyrimidine ring is synthesized first and subsequently attached to the ribose phosphate. DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are the most famous nucleic acids. http://creativecommons.org/licenses/by/4.0/. Since then numerous biochemical and structural analyses have established that nucleic acid sequences, both DNA and RNA, containing runs of guanines (G-tracts) separated by other bases spontaneously fold into G-quadruplex structures in vitro. Figure \(\PageIndex{15}\): Localized Structural Modification of the DNA Double Helix. Proteins and nucleic acids play important biological functions : they catalyze and regulate reactions, transport substrates, code and transcribe genetic information. The associated sequence composition is complex, representing many elaborations during evolution of form and function. RNA, unlike DNA, usually but not always exists in a single-stranded form. The propellor angles for A, B and Z DNA are +18o, + 16 +/-7 o, and about 0o, respectively. Acad. Gene set enrichment (GSE) analysis plays an essential role in extracting biological insight from genome-scale experiments. If it could be possible how would DNA and RNA have to rearrange themselves? As stated, nucleic acid is a specific large molecule that is made up of a polymer or strings that are made up of nucleotides. DNA uses RNA as a sort of protective mechanism, separating the DNA from the chaotic environment of the cytoplasm. DNA and RNA are both needed to build proteins, which are essential for the proper functioning of cells. The prior model was triple-stranded DNA. Dhar, R., Weissman, S.M., Zain, B.S., Pan, J., Lewis, A.M. jr. (1974) Nucl. (2019, July 8). The noncanonical structures are also important for RNA-protein interactions in the RNA region which binds proteins. The 3 bases on the mRNA are called the codon, and the 3 complementary bases on the tRNA are called the anticodon. If you are right-handed, you have right-handed nucleic acids. Figure \(\PageIndex{22}\): Wobble bases pairs using hypoxanthine with the base inosine. A single protein domain that binds adenosine can be used in a wide variety of enzymes. RNA also helps in protein synthesis. What is the role of U(uracil).Why we can't use uracil in DNA or use T(thymine) in RNA, what's the difference between them? These include the Purines: Adenine (A) and Guanine (G), and the Pyrimidines: Cytosine (C) and Thymine (T). Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). The realization that the structure of DNA is that of a double-helix elucidated the mechanism of base pairing by which genetic information is stored and copied in living organisms and is widely considered one of the most important scientific discoveries of the 20th century. This is possible because the chemical properties of nucleotides allow 5 carbons to bond to multiple phosphates. Direct link to Jon Hill's post A creationist would say t, Posted 6 years ago. Download preview PDF. The normal "anti" orientation allows "Watson-Crick" (WC) base pairing between AT and GC base pairs while the altered rotation allows "Hoogsteen" base pairs. What is the basic structure of a nucleic acid? The sugar in DNA is deoxyribose while in RNA it is ribose. We have grown leaps and bounds to be the best Online Tuition Website in India with immensely talented Vedantu Master Teachers, from the most reputed institutions. If A-T bonds have 2 hydrogen bonds and G-C bonds have 3 Would it be true that longer periods of A-T bonds in DNA (so like: AATAATTATTTTAATTAAAA) are less stable parts of the DNA helix than parts that have more (or only) G-C bonds in them? Answer (1 of 11): Nucleic acid is essential for the body of an organism. Which of the following are functions of nucleic acids? a. building and Because nucleic acids can be made naturally by reacting inorganic ingredients together, and because they are arguably the most essential ingredient for life on Earth, some scientists believe that the very first life on Earth may have been a self-replicating sequence of amino acids that was created by natural chemical reactions. Small molecules like urea, as we saw with proteins, can also denature DNA into single strands. In Wikipedia, The Free Encyclopedia. A major function of nucleic acids involves the storage and expression of genomic information. In the nucleus, nucleotide monomers are linked together . In molecular biology shorthand, the nitrogenous bases are often just referred to by their one-letter symbols, A, T, G, C, and U. DNA contains A, T, G, and C, while RNA contains A, U, G, and C (that is, U is swapped in for T). Nucleic acids are formed mainly with the elements carbon, oxygen, hydrogen, nitrogen, and phosphorus. These ribozymes activity often involves a nucleic acid's cleavage. Figure \(\PageIndex{29}\) shows the base pairing of purine and pyrimidines of the third strand to the canonical AT dn GC base pairs of the original double-stranded DNA. The LibreTexts libraries arePowered by NICE CXone Expertand are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Nucleotides are synthesized from readily available precursors in the cell. Purine is salvaged in the form of the corresponding nucleotide, whereas pyrimidine is salvaged as the nucleoside. However as our ability to record information on silicon has advanced, little attention has been given to research into genetic computers.. If you're seeing this message, it means we're having trouble loading external resources on our website. Modulation of Figure \(\PageIndex{xx}\)Hoogsteen dynamics on DNA recognition. Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. Each nucleotide, in turn, is composed of three distinct elements: a five-carbon ribose sugar, a phosphate group and a nitrogenous base. (2019, July 26). Figure \(\PageIndex{6}\) shows types of "secondary (flat representations) and their 3D or tertiary representations found in nucleic acids. Based upon years of work using hydrolysis to break down and analyze yeast nucleic acids, Levene proposed that nucleic acids were composed of a series of nucleotides, and that each. There are two types of nucleic acid: RNA and DNA. They knew its three-dimensional form resembled a double helix, and at least as importantly, they understood that DNA contains the genetic code, or "blueprint," for all organisms (some viruses excepted, and not all scientists accept that viruses are in fact alive). The nucleic acids consists of two major macromolecules, Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) that carry the genetic instructions for the development, functioning, growth and reproduction of all known organisms and viruses. Nucleic acids Flashcards | Quizlet Maniatis, T. Ptashne, M., Backmann, K., Kleid, D., Flashman, S., Jeffrey, A., Maurer, R. (1975) Cell 5, 109113. Retrieved 06:16, July 27, 2019, from en.Wikipedia.org/w/index.php?title=Gene_structure&oldid=906938498. Just as your computer can create entire virtual realities simply by reading strings of 1s and 0s, cells can create entire living organisms by reading strings of the four DNA base pairs. Nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), carry genetic information which is read in cells to make the RNA and proteins by which living things function. Corrections? Z-DNA Unlike others, the Z-DNA is left-handed DNA. these include . A biological polymer made of amino acid monomers is a answer choices protein lipid carbohydrate nucleic acid Question 3 30 seconds Q. The complementarity of the double-stranded DNA model Watson and Crick strongly suggests that semi-conservative replication of the DNA molecule occurs. Lenglet and David-Cordonnier (2010) Journal of Nucleic Acids, http://dx.doi.org/10.4061/2010/290935. What is the 3 roles of nucleic acid? - scienceoxygen.com 1976. The Biological Function of Nucleic Acids. What is a nitrogenous base? Nucleic acids are the main information-carrying molecules of the cell, and, by directing the process of protein synthesis, they determine the inherited characteristics of every living thing. The TFO binds along the major grove of the D2 strand which is purine rich. For example, DNA contains two such chains spiraling round each other in the famous double helix shape. In Wikipedia, The Free Encyclopedia. Let us know if you have suggestions to improve this article (requires login). Provided by the Springer Nature SharedIt content-sharing initiative, Over 10 million scientific documents at your fingertips. What are examples of biological functions? [Facts!] Nucleosome. Could there ever be an instance where there are more than just five kinds of nitrogenous bases (Adenine, Thymine, Guanine, Cytocine and Uracil)?
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