Chapter 8 - Nucleotides and Nucleic Acids

Chapter 8 - Nucleotides and Nucleic Acids - Chapter 8...

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Chapter 8: Nucleotides and nucleic acids 3 classes of RNA 1. Ribosomal RNA (rRNA) – components of ribosome’s, complexes that carry out the synthesis of proteins 2. Messenger RNA (mRNA) – intermediaries, carrying genetic information from one or a few genes to a ribosome, where the corresponding protein can be synthesized 3. Transfer RNA (tRNA) – are adapter molecules that faithfully translate the information in mRNA into a specific sequence of amino acids Nucleotides =>3 characteristics 1. Nitrogenous base 2. pentose 3. phosphate nucleoside => molecule with out phosphate group pyrimidine and purine => bases and pentose of common nucleotides, heterocyclic compounds Bases of nucleotide joined covalently in an N-β-glycosly bond to the 1’ carbon of the pentose, and the phosphate is esterifies to the 5’ carbon. N-β-glycosly bond is formed by removal of the elements of water Major groups of DNA and RNA A,T,C,G DNA extra major group is thymine RNA extra major group is Uracil Two kinds of pentose Recurring deoxyribonucleotide units of DNA contain 2’-deoxy-d-ribose Ribonucleotide units of RNA contain D-ribose DNA minor bases that are most common are methylated forms of the major bases There are many minor bases of RNA Nomenclature Indicate the ring position of the substituent by its number The element to which the substituent is attached is not identified EXOCYCLIC nomenclature Type of atom is identified and the ring position to which it is attached is denoted with a superscript. Ribonucleoside 2’,3’-cyclic monophosphates – phosphate group in position other that 5’, isolatable intermediates Ribonucleoside 3’-monophosphates – products of the hydrolysis of RNA by certain ribbonucleases. DNA and RNA are covalently linked through phosphate group bridges, in which the 5’-phosphate group of one nucleotide unit is joined to the 3’-hydroxyl group of the next nucleotide, creating a phosphodiester linkage DNA and RNA are held together by phosphodiester linkage.
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All have same orientation Linear nucleic acid strand a specific polarity and distinct 5’ and 3’ ends Covalent backbone is subject to slow, nonenzymatic hydrolysis of the phosphodiester bonds. RNA hydrolyzed rapidly under alkaline conditions, but DNA is not 2’-hydroxyl groups in RNA are directly involved in the process. DNA and RNA back bone hydrophilic Hydroxyl groups of the sugar residues form hydrogen bonds with water Phosphate groups pka ≈ 0 =>completely ionized and negatively charged at ph 7 Negative charge generally neutralized by ionic interactions with positive charges on proteins, metal ions, and polyamines Oligonucleotide – short nucleic acid Polynucleotide – long nucleic acid
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Chapter 8 - Nucleotides and Nucleic Acids - Chapter 8...

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