Chapter 4 Nucleic Acids What Are the Building Blocks of DNA What Is a Nucleic Acid A nucleic acid is a polymer of Nucleotides are each composed of The sugar is ribose in ribonucleotides and deoxyribose in deoxyribonucleotides There are two groups of nitrogenous bases purines adenine guanine pyrimidines cytosine uracil and thymine Uracil U is found only in ribonucleotides and thymine T is found only in deoxyribonucleotides Building blocks of nucleic acids Deoxy means lacking Nucleotides Polymerize to Form Nucleic Acids Nucleic acids form when nucleotides polymerize A condensation reaction forms a between the phosphate group on the 5 carbon of one nucleotide and the OH group on the 3 carbon of another Types of nucleotides involved 1 which contain the sugar ribose and form RNA 2 which contain the sugar deoxyribose and form DNA Joins the 5 carbon on the ribose of one nucleotide to the 3 carbon on the ribose of the other Polymerization of nucleic acids is an process catalyzed by enzymes The sugar phosphate backbone of a nucleic acid is directional one end has an unlinked 5 carbon and the other end has an unlinked 3 carbon The nucleotide sequence is written in the direction This reflects the sequence in which nucleotides are added to a growing molecule This nucleotide sequence comprises the nucleic acid s Energy for polymerization comes from the of the nucleotides Phosphorylation is the transfer of one or more phosphate groups to a substrate molecule This raises the potential energy of the substrate and enables endergonic reactions In nucleic acid polymerization two phosphates are transferred creating a Review Backbone of Proteins Primary Secondary Tertiary and Quaternary Structure Written Backbone of DNA and RNA Primary and Secondary Structure DNA and Tertiary and Quaternary RNA Written What is the Nature of DNA s Secondary Structure Erwin Chargaff established two empirical rules for DNA 1 2 Watson and Crick inferred the structure from several pieces of information known at the time What was known DNA was polymerized through phosphodiester linkages Chargaff s two rules Purines Pyrimidines A T C G Wilkins and Franklin X Ray Crystallography showed 3 distances 0 34 nm 2 0 nm and 3 4 nm What structure could explain both Chargaff s rules and the Franklin Wilkins measurements By running the strands anti parallel hydrogen bonds could form between G C pairs and A T pairs James Watson and Francis Crick determined 1 DNA strands run in an 2 DNA strands form a double helix The hydrophilic sugar phosphate backbone faces the exterior Nitrogenous base pairs face the interior 3 Purines always pair with pyrimidines Specifically strands form A T have two hydrogen bonds C G have three hydrogen bonds 4 DNA has two different sized grooves the major groove and the minor groove RNA Structure and Function RNA can also forms secondary structures by folding back on itself and forming H bonds The most common are RNA Structure and Function RNA molecules can also fold into complex shapes to form tertiary and even quaternary structures RNA s can even function as catalytic molecules called
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