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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

Chapter 22 Nucleic Acids and Protein Synthesis

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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.

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Nitrogen Bases

The nitrogen bases in nucleic acids consist of the:

Pyrimidines C, T, and U

And purines A and G.

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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.

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HO

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

Nucleosides

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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.

Nucleotides

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Names of Nucleosides and Nucleotides

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Nucleosides and Nucleotides with Purines

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Nucleosides and Nucleotides with Pyrimidines

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AMP, ADP, and ATP

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

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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.

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Primary Structure of Nucleic Acids

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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’.

Structure of Nucleic Acids

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Example of RNA

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

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Example of DNA

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

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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.

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DNA Double Helix Structure

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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.

DNA Replication

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Hydrolysis Energy Energy from the

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

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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.

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Direction of Replication