Nucleic acids are made up of nucleotides which contain a nitrogenous base, a 5-carbon sugar (either ribose or deoxyribose), and a phosphate group. DNA and RNA are nucleic acids that differ in their sugar and one of their bases. DNA contains the bases adenine, guanine, cytosine, and thymine and uses deoxyribose while RNA contains adenine, guanine, cytosine, and uracil and uses ribose. Nucleic acids form double helix structures through base pairing between complementary bases and phosphate-sugar backbones to store and transmit genetic information.

1. Nucleic Acids
Nucleic Acids
Structures of Nucleic Acids
DNA Replication
RNA and Transcription
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2. Nucleotides
Nucleic acids consist of nucleotides that have
a sugar, nitrogen base, and phosphate
nucleoside
2
Sugar
Base
PO4

3. Nitrogen-Containing Bases
N
N
N
N
H
NH2
N
N
O
CH3
O
H
H
N
N
N
N
O
H
NH2
H
N
N
NH2
CH3
O
H
N
N
O
CH3
O
H
H
adenine (A) thymine (T)
guanine (G) cytosine (C) uracil (U)
3

4. Sugars
O OHCH2
OHOH
HO HO O OHCH2
OH
ribose deoxyribose
(no O)
4

5. Nucleosides in DNA
Base Sugar Nucleoside
Adenine (A) Deoxyribose Adenosine
Guanine (G) Deoxyribose Guanosine
Cytosine (C) Deoxyribose Cytidine
Thymine (T) Deoxyribose Thymidine
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6. Nucleosides in RNA
Base Sugar Nucleoside
Adenine (A) ribose Adenosine
Guanine (G) ribose Guanosine
Cytosine (C) ribose Cytidine
Uracil (U) ribose Uridine
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7. Example of a Nucleoside 7
O
OH
N
N
NH2
O
CH2OP
O
O
-
O
-
deoxyctyidine monophosphate (dCMP)

8. Nucleotides in DNA and RNA
DNA
dAMP Deoxyadenosine monophosphate
dGMP Deoxyguanosine monophosphate
dCMP Deoxycytidine monophosphate
dTMP Deoxythymidine monophosphate
RNA
AMP adenosine monophosphate
GMP guanosine monophosphate
CMP cytidine monophosphate
UMP uridine monophosphate
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9. 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

10. Nucleic Acid Structure
3,5-phosphodiester bond
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O
N
N
NH2
O
CH2OP
O
O
-
O
-
OH
O
N
N
NH2
CH2OP
O
O
-
OH
O
N
N
AMP
CMP
3
5

11. 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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12. Complementary Base Pairs 12
•Two H bonds for A-T
•Three H bonds for G-C

13. Double Helix of DNA 13

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-G-
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15. 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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16. DNA Unwinds
G- -C
A- -T
C- -G
T- -A
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G-
C
A-T
C-
G
T-A

17. DNA Copied with Base Pairs
Two copies of original DNA strand
G-C G-C
A-T A-T
C-G C-G
T-A G-A
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