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Biochemistry

Biochemistry. Lecture 6. Functions of Nucleotides and Nucleic Acids. Nucleotide Functions: Energy for metabolism (ATP) Enzyme cofactors (NAD + ) Signal transduction (cAMP) Nucleic Acid Functions: Storage of genetic info (DNA) Transmission of genetic info (mRNA)

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Biochemistry

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  1. Biochemistry Lecture 6

  2. Functions ofNucleotides and Nucleic Acids • Nucleotide Functions: • Energy for metabolism (ATP) • Enzyme cofactors (NAD+) • Signal transduction (cAMP) • Nucleic Acid Functions: • Storage of genetic info (DNA) • Transmission of genetic info (mRNA) • Processing of genetic information (ribozymes) • Protein synthesis (tRNA and rRNA)

  3. Discovery of DNA Structure • One of the most important discoveries in biology • Why is this important • "This structure has novel features which are of considerable biological interest“ --- Watson and Crick, Nature, 1953 • Good illustration of science in action: • Missteps in the path to a discovery • Value of knowledge • Value of collaboration • Cost of sharing your data too early

  4. Covalent Structure of DNA (1868-1935) • Friedrich Miescher isolates “nuclein” from cell nuclei • Hydrolysis of nuclein: • phosphate • pentose • and a nucleobase • Chemical analysis: • phosphodiester linkages • pentose is ribofuranoside Structure of DNA: 1929 (Levene and London) Structure of DNA: 1935 (Levene and Tipson)

  5. Road to the Double Helix • Franklin and Wilkins: • “Cross” means helix • “Diamonds” mean • that the phosphate- • sugar backbone • is outside • Calculated helical • parameters • Watson and Crick: • Missing layer means • alternating pattern • (major & minor groove) • Hydrogen bonding: • A pairs with T • G pairs with C • Double helix fits the data! Watson, Crick, and Wilkins shared 1962 Nobel Prize Franklin died in 1958

  6. Other forms of DNA

  7. Nucleotide Nucleoside Nucleobase

  8. Pyrimidine Nucleobases

  9. Purine Nucleobases

  10. b-N-Glycosidic Bond

  11. Polynucleotides

  12. Hydrolysis of RNA

  13. Hydrogen Bonding!

  14. The Central Dogma

  15. DNA Replication “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material” Watson and Crick, in their Nature paper,1953

  16. Using DNA Structure

  17. Why detect Transcription Factor targets? • Transcription factors are medically relevant • ~10% of human genes • Crucial roles in development and cell life cycle • Misregulation and mutation cause disease • Critically, most cancers involve TF overactivity Darnell, Nature Reviews Cancer 2, 740 (2002)

  18. Traditional methods for Transcription Factor detection Western Blots Expression Microarrays Gel Shift Assays The challenge: Most of these methods are indirect, slow (hours), or can’t differentiate active and inactive protein.

  19. Velcro: inspired by burrs Conformation Switching Probes Marvin J S et al. PNAS 1997;94:4366-4371 Bio-mimicry is a powerful motivation

  20. Optical Conformation SwitchingTF Switch Sensors

  21. Rationally Tuning TF Sensors KS = 10 [ ] [ ] [ ] KS = KS = 1 KD = [ ] [ ] KS = 0.001 % switches open KS = 0.01 KS = 0.1 KS [target] % switches open = KD (1+ KS) + KS [target] Target [M]

  22. TF Beacon Actual Performance

  23. Quantitative Detection in 4 easy steps

  24. Thermal Denaturation

  25. Molecular Mechanisms of Spontaneous Mutagenesis • Deamination • Very slow reactions • Large number of residues • The net effect is significant: 100 C  U • events /day in a mammalian cell • Depurination • N-glycosidic bond is hydrolyzed • Significant for purines: 10,000 purines • lost/day in a mammalian cell • Cells have mechanisms to correct most of these modifications.

  26. UV Absorption of Nucleobases

  27. Pyrimidine Dimers from UV http://highered.mcgraw-hill.com/olc/dl/120082/micro18.swf

  28. DNA Technologies

  29. DNA Cloning

  30. Restriction Enzymes

  31. PCR Polymerase Chain Reaction

  32. Antibiotic Selection • Antibiotics, such as penicillin and ampicillin, kill bacteria • Plasmids can carry genes that give host bacterium a resistance against antibiotics • Allows growth (selection) of bacteria that have taken up the plasmid

  33. Site-Directed Mutagenesis

  34. Expression of Cloned Genes

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