Nucleic AcidsNucleic Acids

Structures of Nucleic AcidsDNA Replication

RNA and Transcription

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Nucleotides

Nucleic acids consist of nucleotides that have a sugar, nitrogen base, and phosphate

nucleoside

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Sugar

Base

PO4

Nitrogen-Containing Bases

N

N

N

NH

NH2

N

N

OCH3

O

H

H

N

N

N

N

OH

NH2H

N

N

NH2

CH3

OH

N

N

OCH3

O

H

H

adenine (A) thymine (T)

guanine (G) cytosine (C) uracil (U)

3

Sugars

O OHCH2

OHOH

HO HO O OHCH2

OH

ribose deoxyribose

(no O)

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Nucleosides in DNA

Base Sugar NucleosideAdenine (A) Deoxyribose AdenosineGuanine (G) Deoxyribose GuanosineCytosine (C) Deoxyribose CytidineThymine (T) Deoxyribose Thymidine

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Nucleosides in RNA

Base Sugar NucleosideAdenine (A) ribose

AdenosineGuanine (G) ribose

GuanosineCytosine (C) ribose CytidineUracil (U) ribose Uridine

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Example of a Nucleoside 7

O

OH

N

N

NH2

O

CH2OPO

O-O-

deoxyctyidine monophosphate (dCMP)

Nucleotides in DNA and RNADNAdAMP Deoxyadenosine monophosphatedGMP Deoxyguanosine monophosphatedCMP Deoxycytidine monophosphatedTMP Deoxythymidine monophosphate

RNAAMP adenosine monophosphateGMP guanosine monophosphateCMP cytidine monophosphateUMP uridine monophosphate

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Structure of Nucleic Acids

Polymers of four nucleotides Linked by alternating sugar-phosphate bonds RNA: ribose and A, G, C, U DNA: deoxyribose and A,G,C,T

nucleotide nucleotide nucleotide nucleotide

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P sugar

base

P sugar

base

P sugar

base

P sugar

base

Nucleic Acid Structure

3,5-phosphodiester bond

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O

N

N

NH2

O

CH2OPO

O-O-

OH

O

N

N

NH2

CH2OPO

O-

OH

O

N

N

AMP

CMP

3

5

Double Helix of DNA

DNA contains two strands of nucleotides H bonds hold the two strands in a double-

helix structure A helix structure is like a spiral stair case Bases are always paired as A–T and G-C Thus the bases along one strand

complement the bases along the other

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Complementary Base Pairs

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•Two H bonds for A-T•Three H bonds for G-C

Double Helix of DNA 13

Solution NA1

Write the complementary base sequence for the matching strand in the following DNA section:

-A-G-T-C-C-A-A-T-G-C-

• • • • • • • • • • • • • • • • • • • •-T-C-A-G-G-T-T-A-C-G-

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DNA Replication

DNA in the chromosomes replicates itself every cell division

Maintains correct genetic information Two strands of DNA unwind Each strand acts like a template New bases pair with their

complementary base Two double helixes form that are

copies of original DNA

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DNA Unwinds

G- -CA- -TC- -GT- -A

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G-CA-TC-GT-A

DNA Copied with Base Pairs

Two copies of original DNA strand

G-C G-CA-T A-TC-G C-GT-A G-A

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