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Molecular Biology 2.6 Structure of DNA and RNA Nucleic Acids The nucleic acids DNA and RNA are polymers of nucleotides Nucleic Acids Nucleotides A sugar 5 consist of 3 parts: carbon sugars = pentose sugars A base contains nitrogen 1 or 2 rings of atoms 1 ring = Pyrimidine 2 rings = Purine A phosphate group negatively acidic charged Nucleic Acids Covalent bonds are formed between the phosphate of one nucleotide and the sugar of the next. This creates a “backbone” of alternating sugar and phosphate. Nucleic Acids The bonds holding the phosphate group to the sugar and the base to the sugar are both products of condensation reactions. Water is eliminated when they form. The oxygen to form the water has come from the sugar's -OH groups. Nucleic Acids DNA differs from RNA in the number of strands normally present, the base composition and the type of pentose Make a chart DNA # of strands Base composition Sugar RNA Nucleic Acids DNA has 2 polymers of nucleotides (double-stranded) RNA has 1 polymer (single-stranded) Nucleic Acids The sugar within DNA is deoxyribose The sugar with RNA is ribose Draw both sugars. Compare the structures. Predict the reason for the difference in their names. Compare to the previously examined carbohydrate sugars. Nucleic Acids There are 4 different bases for each type of nucleic acid These can be linked in any sequence Draw the 2 generic base types. Complete the “databased question” p109 Nucleic Acids Data-based #1 Nucleic Acids Data-based question #2 Nucleic Acids Data-based #3 and #4 Nucleic Acids The amino acid sequence of polypeptides is coded for by genes The sequence of nucleotide bases provides the code 3 bases of the gene are needed to code for each amino acid More about this later Nucleic Acids The variety of combinations of bases is the key to nucleic acids acting as a store of genetic information. Nucleic Acids DNA Pyrimidines = Thymine (T) and Cytosine (C) Purines = Adenine (A) and Guanine (G) Nucleic Acids RNA Pyrimidines = Uracil (U) and Cytosine (C) Purines = Adenine (A) and Guanine (G) Note the change from T to U Nucleic Acids DNA is a double helix made of 2 antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs Nucleic Acids The strands are held together by hydrogen bonds between the complementary base pairs. Adenine always pairs with Thymine Guanine always pairs with Cytosine The 2 strands are parallel but run in opposite directions one runs 5’ to 3’ the other 3’ to 5’ Nucleic Acids Draw simple diagrams of DNA using circles, pentagons, and rectangles to represent phosphates, pentoses, and bases. The base is attached to the C1 The phosphate is linked to the C5 The phosphate of another nucleotide will link to the C3 Review quiz http://www.rsc.org/Education/Teachers/R esources/cfb/quiz.cfm?qzid=15
