LS1a_L12_notes08-1

LS1a_L12_notes08-1 - LIFE S CI ENC 1a ES PROF. ROBERT LUE...

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PROF. ROBERT LUE OCTOBER 23, 2008 1a L I F E S C I E N C E S 1
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Nucleic acids and the chemistry of replicating information 1. The biological role of DNA - Information storage in DNA 2. Double helix structure of DNA - The bases of DNA and base pairing; redundancy - The sugar group in DNA; strand orientation - The chemical driving force for the double helix structure 3. Chemical interactions involving DNA - The phosphate group in DNA; physiological consequences - Major & minor grooves; DNA-binding proteins 2
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DNA is a double helix made up of nucleotides O O N N N NH 2 O N P O O O Base Sugar Phosphate Polymer Monomer Nucleic acids are polymers of nucleotides Each nucleotide consists of a phosphate, a sugar, and a nitrogenous base The primary structure of DNA The information carrying function of DNA depends on the four different nitrogenous bases, but each base is part of a so-called nucleotide monomer that includes a deoxyribose sugar and a phosphate group. Thus, DNA is a polymer consisting of nucleotides. Each of your cells contains ~6,200,000,000 DNA nucleotides. The four bases, when connected to just a deoxyribose sugar, are called the nucleosides adenosine, cytidine, guanosine, and thymidine. As you have learned before, DNA exists in the cell as a double-stranded polymer, meaning that two chains of nucleotides are closely associated with each other. In two dimensions, you can think of double-stranded DNA as a ladder. In three dimensions, double-stranded DNA usually adopts its famous “double helix” structure. 3
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Watson-Crick base pairing O O P O O O N N N N N O H H N N CH 3 O O H O O P O O O O adenosine A thymidine T O O P O O O N N N N O N H H H O O P O O O N O N N O H H cytidine C guanosine G Each base displays a unique arrangement of hydrogen bond donors and acceptors that can pair when juxtaposed Width of the double stranded molecule is fairly constant Bases are precisely arranged to form hydrogen bonds Although A, C, G, and T differ in structure, they share some important common features. In addition to being planar heterocycles, all four bases contain a nitrogen atom that in DNA is covalently bonded with the 1’ carbon atom of deoxyribose. Also, the four DNA bases each contain a unique constellation of hydrogen bond donors and acceptors. The donors and acceptors are precisely arranged such that A can form two hydrogen bonds with T, and C can form three hydrogen bonds with G at every nucleotide position within double- stranded DNA. James Watson and Francis Crick are credited with first deducing that A pairs with T and G pairs with C in the manner shown here. Watson and Crick apparently knew this discovery was important, as they walked into the Eagle Pub in Cambridge, England on February 28, 1953 and announced to the pub patrons “We have found the secret of life!”. Their seminal 1953 discovery was recognized with the 1962 Nobel Prize in Physiology or Medicine, awarded to Watson, Crick, and their collaborator Maurice Wilkins.
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LS1a_L12_notes08-1 - LIFE S CI ENC 1a ES PROF. ROBERT LUE...

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