8. nucleotides and nucleic acids chapter 8 lehninger 5 th ed
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8. Nucleotides and Nucleic Acids
Chapter 8 Lehninger 5th ed.
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Nucleotides
• “Energy rich” compounds– Chemical signals– Enzyme co-factors
• Nucleic Acids– DNA and RNA– Polymers of nucleotides
• 3 components– Nitrogenous “base”– Ribose (or deoxyribose)– Phosphate
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“Bases”
•Bases•Pyrimidines•Purines
•2 pyrimidine bases (in DNA)•Cytosine: C•Thymine: T
•or Uracil: U(in RNA, instead of Thymine)
A G•2 purine bases
•Adenine: A•Guanine: G
C T U
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Ribose• carbons numbered:
– 1’,2’,3’,4’,5’
• DNA: – 2’ Deoxyribose
– or just deoxyribose
2’3’
4’
5’
1’
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Nucleotides
SummaryDNA A,C,G,T
deoxyriboseRNA A,C,G,U
ribose
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Polymerise Nucleotides
• nucleotides can be linked– phosphates linked to 2 pentoses
– phosphodiester linkages• Link PO4 at
– 5’ end to 3’ OH of next nucleotide
• chain has POLARITY–distinct ends
•5’ end•3’ end
–usually “read” 5’ -> 3’
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Nucleotides as Energy Carriers
• ATP – Adenosine triphosphate
• ADP, AMP– Adenosine diphosphate
– Adenosine monophosphate
ATP ADP + PO4
ADP AMP + PO4
• Main energy exchange reactions in cells
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Structure of DNA?• The Genetic Material• Crick and Watson
– Race with Linus Pauling to predict structure
• Chargaff’s rules:– Chemical analysis:
[A] = [T][G] = [C]
– Constant • for each organism
– over time– across all tissues
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X-Ray Diffraction• Predict
– Double helix
– 2 periodicities• 3.4Å
• 34Å
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Base Pairing
• A – T basepair– 2 h-bonds
• G – C basepair– 3 h-bonds
• 2 anti-parallelDNA strands
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The Double Helix
• 3.4Å per basepair• 10 basepairs per turn
– 10-11 in aqueous solution
• 2 anti-parallel strands
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• DNA Replication• By DNA Polymerase
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RNA
• Usually single stranded• Genetic material of RNA virus• Functional:
– e.g. Translation machinery• rRNA (ribosomal RNA)• tRNA (transfer RNA)
• Regulatory:– Control of gene expression
• miRNA (microRNA)
• Gene Expression– mRNA (messenger RNA)– Copy of 1 gene for translation by ribosomes
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RNA Secondary Structure
• RNA single stranded• Can form base pairs internally
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RNA Secondary Structure
• Many functional RNAs have secondary structure
• G-U basepairs allowed
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DNA Sequencing
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DNA Sequencing