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Nucleic Acids
The nucleic acids DNA and
RNA
consist of monomers called
nucleotides that consist of a
• Pentose sugar.
• Nitrogen-containing base.
• Phosphate.
nucleotide
Nitrogen Bases
The nitrogen bases in
DNA and RNA are
• Pyrimidines C, T, and U
• Purines A and G.
Pentose Sugars
The pentose (five-carbon) sugar
• In RNA is ribose.
• In DNA is deoxyribose with no O atom on
carbon 2’.
• Has carbon atoms numbered with primes to
distinguish them from the atoms in nitrogen
bases.
Nucleosides
A nucleoside
• Has a nitrogen base linked by a
glycosidic bond to C1’ of a sugar
(ribose or deoxyribose).
• Is named by changing the the
nitrogen base ending to
• -osine for purines and
-idine for pyrimidines.
HO
Nucleotides
A nucleotide
• Is a nucleoside that forms a
phosphate ester with the
C5’ –OH group of a sugar
(ribose or deoxyribose).
• Is named using the name of
the nucleoside followed by
5’-monophosphate
Nucleosides and Nucleotides
with Purines
Nucleosides and Nucleotides
with Pyrimidines
Primary Structure of Nucleic
Acids
Structure of RNA
The primary
structure of RNA
• Is a single strand of
nucleotides.
• Consists of the
bases A, C, G, and
U linked by 3’-5’
ester bonds between
ribose and
phosphate.
Structure of DNA
In the primary
structure of DNA,
A, C, G, and T
are linked by 3’-5’
ester bonds between
deoxyribose and
phosphate.
Data of Erwin Chargaff
Organism
%A
%T
%C
%C
A/T
G/C
Maize
Octopus
Chicken
Human
Rat
Wheat
E.coli
X174
26.8
33.2
28.0
29.3
28.6
27.3
24.7
24.0
27.2
31.6
28.4
30.0
28.4
27.1
23.6
31.2
22.8
17.6
22.0
22.0
22.0
22.0
22.0
22.0
23.2
17.6
21.6
20.0
20.5
22.8
25.7
21.5
1.0
1.1
1.0
1.0
1.0
1.0
1.1
0.8
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.1
Chargaff’s Rules: %A = %T; %G = %C
X–Ray Diffraction Pattern of DNA
Helical Cross
DNA Secondary Structure
Double Helix
DNA Replication
Watson-Crick Idea
“It has not escaped our notice that the specific pairing we have
postulated immediately suggests a possible copying mechanism
for the genetic material.”
Watson, J.D and F.H.C. Crick
Nature 171, 737-738 (1953)
DNA Replication
DNA Replication
Transcription: DNA to RNA
Transcription of mRNA
tRNA Structure
Induction of genes normally repressed
(Inducer)
Negative Regulation
(bound repressor + corepressor inhibits transcription)
Repression of genes normally expressed
corepressor
Posttranscriptional Processing
of mRNA
Genetic Code
Protein Synthesis
Amino Acid Activation
Transfer energized
amino acid to its
specific tRNA.
Energize the amino
acid. Costs equivalent
to 2 ATP.
Protein
Synthesis
Translation
Protein Synthesis:
Role of Polysomes
Antibiotics: Inhibitors
of Protein Synthesis
Streptomycin: inhibits initiation and
causes misreading of the genetic code
Tetracyclines: inhibit binding of aa-tRNA
Chloramphenicol: inhibits peptide bond
formation
Erthromycin: inhibits translocation
Mutations
Recombinant DNA
Polymerase Chain Reaction (PCR)
3’
5’
Third
Cycle
Second
Cycle
First
Cycle
5’
3’
heat to separate
the two strands
add primers,
cool to 55oC
use DNA
polymerase,
to extend chains
heat to separate
the two strands
heat to separate
the two strands
add primers,
cool to 55oC
use DNA
polymerase,
to extend chains
add primers,
cool to 55oC
use DNA
polymerase,
to extend chains
DNA Fingerprinting
Retrovirus Action
AIDS Virus and Treatment
Examples of protease inhibitors:
saquinavir, indinavir, ritonavir
Examples of non-nucleoside
reverse transcriptase inhibitors:
etravirine, efavirenz, nevirapine
AZT (3’-azido-3’deoxythymidine)
(nucleoside analog reverse
transcriptase inhibitor)