Nucleic Acids
Nucleotides
Nucleic acids consist of nucleotides that have a
sugar, nitrogen base, and phosphate
Nucleic Acids
Structures of Nucleic Acids
DNA Replication
RNA and Transcription
Base
PO4
Sugar
nucleoside
1
2
Nitrogen-Containing Bases
O
NH2
H
N
N
N
N
NH2
N
N
H
guanine (G)
HOCH2
N
thymine (T)
NH 2
OH
HOCH2
O
OH
O
O
CH3
N
H
N
O
H
CH3
N
OH
OH
(no O)
deoxyribose
H
cytosine (C)
Sugar
Deoxyribose
Deoxyribose
Deoxyribose
Deoxyribose
OH
ribose
N
uracil (U)3
Nucleosides in DNA
Base
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
O
H
N
N
CH3
N
O
H
adenine (A)
O
H
Sugars
4
Nucleosides in RNA
Nucleoside
Adenosine
Guanosine
Cytidine
Thymidine
Base
Adenine (A)
Guanine (G)
Cytosine (C)
Uracil (U)
5
Sugar
ribose
ribose
ribose
ribose
Nucleoside
Adenosine
Guanosine
Cytidine
Uridine
6
1
Nucleotides in DNA and RNA
Example of a Nucleoside
NH2
N
O
O
O-
P O CH2
-
N
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
O
O
OH
deoxyctyidine monophosphate (dCMP)
7
Structure of Nucleic Acids
8
Nucleic Acid Structure
NH2
•
•
•
•
N
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
base
base
CMP
O
O
-
O
P O CH2
-
O
P
P
nucleotide
sugar
P
sugar
O
3
NH2
OH
base
3,5-phosphodiester bond
sugar
P
sugar
N
O
5
O P O CH2
O-
N
N
N
N
O
AMP
nucleotide nucleotide nucleotide
9
Double Helix of DNA
OH
10
Complementary Base Pairs
•Two H bonds for A-T
•Three H bonds for G-C
• 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
11
12
2
Learning Check
Double Helix of DNA
Write the complementary base sequence for
the matching strand in the following DNA
section:
-A-G-T-C-C-A-A-T-G-C• •
• •
• • • • • • • •
• • • • • • • •
13
14
DNA Replication
DNA Unwinds
• 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 helices form that are copies of original
DNA
16
G-C
A-T
C-G
T-A
GACT-
-C
-T
-G
-A
17
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
•
•
•
18
3