Chapter 4 Nucleic Acids What Are the Building Blocks of DNA Review Session Next Wednesday September 26th from 5 30 6 30 pm Will be in room 1213 No new information will be covered only a review and time for you to ask questions about the material for the exam Exam will cover Chapters 1 5 What Is a Nucleic Acid 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 Watson and Crick inferred the structure from several pieces of information known at the time What is the Nature of DNA s Secondary Structure Erwin Chargaff established two empirical rules for DNA 1 2 Building blocks of nucleic acids Chemists had worked out the structure of nucleotides and knew that DNA was polymerized through the formation of As a result Watson and Crick knew the molecule had to have a What is the Nature of DNA s Secondary Structure Rosalind Franklin and Maurice Wilkins had performed experiments where they bombarded DNA with X ray crystallography and analyzed how it scattered the radiation Calculated three repeating distances By running the strands anti parallel hydrogen bonds could form Watson and Crick inferred the structure from several pieces of information known at the time What structure could explain both Chargaff s rules and the Franklin Wilkins measurements 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 Watson and Crick s Model Revealed how DNA might biological information Complementary base pairing allows each strand of a DNA double helix to be producing two identical copies DNA s primary structure serves as a RNA Differs from DNA Structurally DNA contains that can participate in chemical reactions The lack of a on each deoxyribonucleotide makes the polymer much reactive than RNA and more resistant to degradation RNA Structure and Function The hydroxyl group on the 2 carbon is much more reactive making RNA RNA can also form by folding back on itself and forming H bonds The most common are hairpin structures 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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