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8. Nucleotides and Nucleic Acids

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1 8. Nucleotides and Nucleic Acids
Chapter 8 Lehninger 5th ed.

2 Nucleotides “Energy rich” compounds Nucleic Acids 3 components
Chemical signals Enzyme co-factors Nucleic Acids DNA and RNA Polymers of nucleotides 3 components Nitrogenous “base” Ribose (or deoxyribose) Phosphate

3 “Bases” A G C T U 2 purine bases Bases 2 pyrimidine bases (in DNA)
Adenine: A Guanine: G A G Bases Pyrimidines Purines C T U 2 pyrimidine bases (in DNA) Cytosine: C Thymine: T or Uracil: U (in RNA, instead of Thymine)

4 Ribose carbons numbered: DNA: 1’,2’,3’,4’,5’ 2’ Deoxyribose
or just deoxyribose 5’ 1’ 4’ 3’ 2’

5 Nucleotides Summary DNA A,C,G,T deoxyribose RNA A,C,G,U ribose

6 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’

7 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

8 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

9 X-Ray Diffraction Predict Double helix 2 periodicities 3.4Å 34Å

10 Base Pairing A – T basepair G – C basepair 2 anti-parallel DNA strands
2 h-bonds G – C basepair 3 h-bonds 2 anti-parallel DNA strands

11 The Double Helix 3.4Å per basepair 10 basepairs per turn
10-11 in aqueous solution 2 anti-parallel strands

12 DNA Replication By DNA Polymerase

13 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

14 RNA Secondary Structure
RNA single stranded Can form base pairs internally

15 RNA Secondary Structure
Many functional RNAs have secondary structure G-U basepairs allowed

16 DNA Sequencing

17 DNA Sequencing


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