nucleic acids the nucleic acids dna and rna consist of monomers called nucleotides that consist of a...
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Nucleic AcidsThe nucleic acids DNA and
RNAconsist of monomers callednucleotides that consist of a• Pentose sugar.• Nitrogen-containing base.• Phosphate.
nucleotide
Nitrogen Bases
The nitrogen bases inDNA and RNA are • Pyrimidines C, T, and U • Purines A and G.
Pentose SugarsThe 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.
HO
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.
Nucleosides
A nucleotide • Is a nucleoside that forms a
phosphate ester with the C5’ –OH group of a sugar (ribose or deoxyribose).
Nucleotides
• 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 RNAThe primarystructure 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 DNAIn the primarystructure of DNA, A, C, G, and T are linked by 3’-5’ester bonds betweendeoxyribose andphosphate.
Data of Erwin Chargaff
Organism %A %T %C %C A/T G/C
Maize 26.8 27.2 22.8 23.2 1.0 1.0Octopus 33.2 31.6 17.6 17.6 1.1 1.0Chicken 28.0 28.4 22.0 21.6 1.0 1.0Human 29.3 30.0 22.0 20.0 1.0 1.0Rat 28.6 28.4 22.0 20.5 1.0 1.0Wheat 27.3 27.1 22.0 22.8 1.0 1.0E.coli 24.7 23.6 22.0 25.7 1.1 1.0Φ 174X 24.0 31.2 22.0 21.5 0.8 1.1
Chargaff’s Rules: %A = %T; %G = %C
X–Ray Diffraction Pattern of DNA
Helical Cross
DNA Secondary Structure Double Helix
DNA ReplicationWatson-Crick Idea
5’– AGTACTGGCATCG – 3’3’– TCATGACCGTAGC – 5’
5’– AGTACTGGCATCG – 3’3’– TCATGACCGTAGC – 5’
5’– AGTACTGGCATCG – 3’3’– TCATGACCGTAGC – 5’
“It has not escaped our notice that the specific pairing we havepostulated immediately suggests a possible copying mechanismfor the genetic material.”
Watson, J.D and F.H.C. CrickNature 171, 737-738 (1953)
G
3’ OH
P
C
C
T
T
G
P
P
P
5’
P3’
P
P
P
5’
A
AO P OO P
O O
O P
O
O O O
3’ OH
5’
OHO P
O
O P
O
O O
G
P
C
C
T
T
G
P
P
P
5’
P3’
P
P
P
5’
A
AP
3’ OH
H2O
O P OH
O
O
2
DNA Replication
DNA Replication
Transcription: DNA to RNA
Transcription of mRNA
tRNA Structure
(Inducer)
Induction of genes normally repressed
Negative Regulation(bound repressor + corepressor inhibits transcription)
Repression of genes normally expressed
corepressor
Posttranscriptional Processingof mRNA
Genetic Code
Protein SynthesisAmino Acid Activation
Energize the aminoacid. Costs equivalentto 2 ATP.
Transfer energizedamino acid to itsspecific tRNA.
Protein SynthesisTranslation
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)
heat to separate the two strands
add primers, cool to 55oC
use DNA polymerase, to extend chains
5’3’
3’5’
FirstCycle
SecondCycle
heat to separate the two strands
ThirdCycle
heat to separate the two strands
add primers, cool to 55oC
add primers, cool to 55oC
use DNA polymerase, to extend chains
use DNA polymerase, to extend chains
DNA Fingerprinting
Retrovirus Action
AIDS Virus and Treatment
AZT (3’-azido-3’deoxythymidine)(nucleoside analog reverse
transcriptase inhibitor)
Examples of protease inhibitors:saquinavir, indinavir, ritonavir
Examples of non-nucleosidereverse transcriptase inhibitors: etravirine, efavirenz, nevirapine