Chapter 22 Nucleic Acids and Protein Synthesis 22.1 Components of Nucleic Acids 22.2 Nucleosides and Nucleotides 22.3 Primary Structure of Nucleic Acids 22.4 DNA Double Helix: A Secondary Structure 22.5 DNA Replication

Nucleic Acids Nucleic acids are: Molecules that store information for cellular growth and reproduction. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Large molecules consisting of long chains of monomers called nucleotides.

Nitrogen Bases The nitrogen bases in nucleic acids consist of the: Pyrimidines C, T, and U And purines A and G.

Pentose Sugars The pentose (five-carbon) sugar: In RNA is ribose. In DNA is deoxyribose. Has carbon atoms numbered with primes to distinguish them from the nitrogen bases.

Nucleosides A nucleoside: Has a nitrogen base linked by a glycosidic bond to C1’ of a ribose or deoxyribose. Is named by changing the the nitrogen base ending to -osine for purines and –idine for pyrimidines HO

Nucleotides A nucleotide: Is a nucleoside that forms a phosphate ester with the C5’ OH group of ribose or deoxyribose. Is named using the name of the nucleoside followed by 5’-monophosphate.

Names of Nucleosides and Nucleotides

Nucleosides and Nucleotides with Purines

Nucleosides and Nucleotides with Pyrimidines

AMP, ADP, and ATP Adding phosphate groups to AMP forms the diphosphate ADP and the triphosphate ATP.

Primary Structure of Nucleic Acids In the primary structure of nucleic acids: Nucleotides are joined by phosphodiester bonds. The 3’-OH group of the sugar in one nucleotide forms an ester bond to the phosphate group on the 5’-carbon of the sugar of the next nucleotide.

Primary Structure of Nucleic Acids

Structure of Nucleic Acids A nucleic acid polymer: Has a free 5’-phosphate group at one end and a free 3’-OH group at the other end. Is read from the free 5’-end using the letters of the bases. This example reads 5’—A—C—G—T—3’.

Example of RNA In RNA, A, C, G, and U are linked by 3’-5’ ester bonds between ribose and phosphate.

Example of DNA In DNA, A, C, G, and T are linked by 3’-5’ ester bonds between deoxyribose and phosphate.

DNA Double Helix In DNA: There are two strands of nucleotides that wind together in a double helix. Two hydrogen bonds form between the complementary base pairs A-T. Three hydrogen bonds form between the complementary base pairs G-C.

DNA Double Helix Structure

DNA Replication DNA replication involves: Unwinding the DNA Pairing the bases in each strand with new bases to form new complementary strands. Producing two new DNA strands that exactly duplicate the original DNA.

Hydrolysis Energy Energy from the hydrolysis of each nucleoside triphosphate adding to the complementary strand is used to form the phosphodiester bond.

Direction of Replication During replication, helicase unwinds the parent DNA at several sections. At each open DNA section called a replication fork, DNA polymerase catalyzes the formation of 5’-3’ester bonds of the leading strand. The lagging strand, which grows in the 3’-5’ direction, is synthesized in short sections called Okazaki fragments. The Okazaki fragments are joined by DNA ligase to give a single 3’-5’ DNA strand.

Direction of Replication