Chapter Outline 14 1 Nucleic Acid Building Blocks

Chapter Outline 14. 1 Nucleic Acid Building Blocks 14. 2 Nucleoside di- and Triphosphates, Cyclic Nucleotides 14. 3 Polynucleotides 14. 4 DNA Structure 14. 7 DNA Replication 14. 8 RNA 14. 9 Translation 1

14. 1: Nucleic Acid Building Blocks • • Nucleic acids consist of nucleotide residues. Each nucleotide is put together from three building blocks: 1) phosphoric acid 2) a monosaccharide 3) an organic base 2

Two types of Bases: 3

Nucleosides: A G C U In RNA A G C T In DNA 4

Nucleotides: 5

14. 2: Nucleoside di- and Triphosphates, Cyclic Nucleotides 6

Dinucleotides 7

14. 3: Polynucleotides in DNA: 8

Polynucleotides in RNA: 9

14. 4 DNA Structure The structure of DNA is understood in terms of three levels of structure: 1) primary (sequence of nucleotide residues) 2) secondary 3) tertiary 10

Secondary Structure • In DNA, secondary structure pertains to the helix formed by the interaction of two DNA strands. • In the most commonly found form of DNA, two single strands lie side by side in an antiparallel arrangement, with one running 5’ to 3’ and the other running 3’ to 5’. • The two DNA strands are held to one another by base pairing, hydrogen bonding between the bases attached to the sugar-phosphate backbone. • This base pairing is complementary, which means that A forms hydrogen bonds with T and G forms hydrogen bonds with C. 11

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Base Pairing: 13

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DNA Replication: • When DNA is replicated, each strand of the double helix serves as a template for the manufacture of a new strand of DNA. • In each of the daughter DNA strands, one strand from the parent DNA is present. • This is called semiconservative replication. 15

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14. 8: RNA differs from DNA in that: 1) It contains a different monosaccharide residue 2) It contains the bases A, G, C, and U instead of A, G, C, and T 3) It exists as a single strand instead of a double strand The first step in using the information stored in DNA to produce proteins is transcription - using DNA as a template to make RNA. 17

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Three Types of RNA 1) 2) 3) Transfer RNA (t. RNA) are the smallest of the three types (73 -93 nucleotide residues), and they carry the correct amino acid to the site of protein synthesis. Messenger RNA (m. RNA) are of variable size, depending on the protein to be manufactured, and carry the information that specifies which protein should be made. This message is carried as a sequence of nucleotides that is complementary to the template strand of DNA. Ribosomal RNAs (r. RNA) are relatively long RNA strands (hundreds or thousands of nucleotide residues) that combine with proteins to form ribosomes, the multisubunit complexes in which protein synthesis takes place. 19

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14. 9: Translation 21

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