1 22.1 components of nucleic acids 22.2 nucleosides and nucleotides 22.3 primary structure of...
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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