1. Nucleic acids consist of nucleotides which contain a nitrogenous base, a 5-carbon sugar (ribose in RNA and deoxyribose in DNA), and a phosphate group. 2. The four nitrogenous bases in DNA are adenine, guanine, cytosine, and thymine, while in RNA thymine is replaced by uracil. 3. Nucleotides are linked together by phosphodiester bonds between the sugar of one nucleotide and the phosphate of the next, forming long chains that make up DNA and RNA.

1. 1
Nucleic Acids
Nucleic Acids
Structures of Nucleic Acids
Structure of DNA
Nucleotides

2. 2
Nucleotides
Nucleic acids consist of nucleotides that
have a sugar, nitrogen base, and phosphate
nucleoside
Sugar
Base
PO4

3. 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)

4. 4
Sugars
O OH
CH2
OH
OH
HO HO O OH
CH2
OH
ribose deoxyribose
(no O)

5. 5
Nucleosides in DNA
Base Sugar Nucleoside
Adenine (A) Deoxyribose Adenosine
Guanine (G) Deoxyribose Guanosine
Cytosine (C) Deoxyribose Cytidine
Thymine (T) Deoxyribose Thymidine

6. 6
Nucleosides in RNA
Base Sugar Nucleoside
Adenine (A) ribose Adenosine
Guanine (G) ribose Guanosine
Cytosine (C) ribose Cytidine
Uracil (U) ribose Uridine

7. 7
Example of a Nucleoside
O
OH
N
N
NH2
O
CH2
O
P
O
O
-
O-
deoxyctyidine monophosphate (dCMP)

8. 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

9. 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
P sugar
base
P sugar
base
P sugar
base
P sugar
base

10. 10
Nucleic Acid Structure
3,5-phosphodiester bond
O
N
N
NH2
O
CH2
O
P
O
O
-
O
-
OH
O
N
N
NH2
CH2
O
P
O
O-
OH
O
N
N
AMP
CMP
3
5

11. 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

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

13. 13
Double Helix of DNA

14. 14

15. 15
Question ?
Write the complementary base sequence
for the matching strand in the following
DNA section:
-A-G-T-C-C-A-A-T-G-C-
• • • • • • • • • •
• • • • • • • • • •

16. 16
Solution
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-

17. 17
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

18. 18
DNA Unwinds
G- -C
A- -T
C- -G
T- -A
G-C
A-T
C-G
T-A

19. 19
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