Chapter 4 Notes

Chapter 4 Notes - Chapter 4 Notes Nucleic Acids and the RNA World Many researches believe that life began as a polymer called nucleic acid RNA

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Chapter 4 Notes Nucleic Acids and the RNA World Many researches believe that life began as a polymer called nucleic acid – RNA o “RNA world hypothesis” Chemical evolution led to the existence of an NA molecule that could make a copy of itself o Chance errors made variations that underwent natural selection 4.1 What Is a Nucleic Acid? Nucleic acids: polymers made up of monomers called nucleotides Three components of a nucleotide: o Phosphate group o A sugar o A nitrogenous base Phosphate bonded to the sugar molecule which is bonded to the nitrogenous base Sugar: organic compound with a carbonyl group and several hydroxide groups Ribonucleotides: sugar is ribose, hydroxide group on 2’ carbon Deoxyribonucleotides: sugar is deoxyribose, H on 2’ carbon (deoxy = lacking carbon) Cells have four different ribonucleotides each with a different nitrogenous base o Bases belong to groups called purines and pyrimidines o Ribonucleotides have the purines adenine (A) and guanine (G) and the pyrimidines cytosine (C) and uracil (U) o Deoxyribonucleotides have AG and C but instead of uracil they have thymine (T) Could Chemical Evolution Result in the Production of Nucleotides? “Ribose problem” A mechanism for the synthesis of pyrimidines has not been discovered How Do Nucleotides Polymerize to Form Nucleic Acids? ***Nucleic acids form when nucleotides polymerize Bond between the phosphate group of one nucleotide and hydroxyl group of the sugar component of another nucleotide o Result is phosphodiester linkage When the nucleotides involved contain the sugar ribose, the polymer that is produced is called ribonucleic acid (RNA) If they include deoxyribose instead, then deoxyribonucleic acid or DNA DNA and RNA Strands are Directional o The sugar-phosphate backbone of a nucleic acid is directional o In RNA or DNA one end has an unlinked 5’ carbon and the other end has an unlinked 3’ carbon (unlinked: not linked to another nucleotide) o Written in 5’ 3’ direction o The sequence of nitrogenous bases forms the primary structure of the molecule Polymerization is an Endergonic Process o Polymerization reactions that form nucleotides are catalyzed by enzymes
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o Phosphorylated: the addition of a phosphate group to a molecule o The addition of one or more phosphate groups raises the potential energy of substrate molecules enough to make an otherwise endergonic reaction possible o Nucleic acid polymerization “activated” Could Nucleic Acids Form in the Prebiotic Soup? o
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This note was uploaded on 02/12/2012 for the course SCI 2341 taught by Professor Yates during the Spring '11 term at Alabama.

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Chapter 4 Notes - Chapter 4 Notes Nucleic Acids and the RNA World Many researches believe that life began as a polymer called nucleic acid RNA

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