Nucleic Acids

Nucleic Acids Nucleic Acids Structures of Nucleic Acids DNA Replication RNA and Transcription

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

PO4 Sugar nucleoside 2

Nitrogen-Containing Bases O

NH2 N

N N

N

H

NH2

N

N H

guanine (G)

N H thymine (T) NH2

N

N

N

O

H adenine (A) O H

CH3

CH3

N O

N H cytosine (C)

O H O

CH3

N N H

uracil (U)3

Sugars HOCH2 O

OH ribose

OH

OH

HOCH2 O

OH

OH

(no O)

deoxyribose 4

Nucleosides in DNA Base Adenine (A) Guanine (G) Cytosine (C) Thymine (T)

Sugar Deoxyribose Deoxyribose Deoxyribose Deoxyribose

Nucleoside Adenosine Guanosine Cytidine Thymidine

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Nucleosides in RNA Base Adenine (A) Guanine (G) Cytosine (C) Uracil (U)

Sugar ribose ribose ribose ribose

Nucleoside Adenosine Guanosine Cytidine Uridine

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Example of a Nucleoside NH2 N O -

O

O

P O CH2 -

O

N

O

OH deoxyctyidine monophosphate (dCMP)

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Nucleotides in DNA and RNA DNA dAMP dGMP dCMP dTMP

Deoxyadenosine monophosphate Deoxyguanosine monophosphate Deoxycytidine monophosphate Deoxythymidine monophosphate

RNA AMP GMP CMP UMP

adenosine monophosphate guanosine monophosphate cytidine monophosphate uridine monophosphate 8

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 base

P

sugar

nucleotide

base

P

sugar

base

P

sugar

base

P

sugar

nucleotide nucleotide nucleotide

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Nucleic Acid Structure NH2 N O

O -

O

P O CH2 -

O

CMP N

O

3

NH2

3,5-phosphodiester bond

OH O

5

O P O CH2 -

O

N

N N O

N AMP

OH

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Double Helix of DNA • DNA contains two strands of nucleotides • H bonds hold the two strands in a doublehelix 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 •Two H bonds for A-T •Three H bonds for G-C

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Double Helix of DNA

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Learning Check 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• • • •

• • • • • • • • • • • • • • • • 14

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-G15

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 16

DNA Unwinds

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

GACT-

-C -T -G -A

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DNA Copied with Base Pairs Two copies of original DNA strand

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

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

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