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RNA ： Cyt 、 Ura

RNA ： Cyt 、 Ura. DNA ： Thy. Many steps require an activated ribose sugar. The committed step in the do novo synthesis of purine nucleotides. Purine Biosynthesis (de novo). (A bunch of steps you don ’ t need to know). IMP. (Inosine Monophosphate). ATP. GTP. AMP. GMP. Feedback

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RNA ： Cyt 、 Ura

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  1. RNA：Cyt、Ura

  2. DNA：Thy

  3. Many steps require an activated ribose sugar

  4. The committed step in the do novo synthesis of purine nucleotides

  5. Purine Biosynthesis (de novo) (A bunch of steps you don’t need to know) IMP (Inosine Monophosphate) ATP GTP AMP GMP Feedback Inhibition

  6. The synthesis of AMP and GMP from IMP

  7. The pyrimidine biosynthetic pathway

  8. CTP synthesis from UTP

  9. Biosynthesis: Purine vs Pyrimidine Purine Pyrimidine • Synthesized on PRPP • Regulated by GTP/ATP • Generates IMP • Requires Energy • Synthesized then added to PRPP • Regulated by UTP • Generates UMP/CMP • Requires Energy Both are very complicated multi-step process which your kindly professor does not expect you to know in detail

  10. Hydroxyurea • Specifically inhibits ribonucleotide reductase NDP dNDP • Inhibits DNA synthesis without affecting RNA synthesis or other nucleotide pools • Cleared from the body rapidly so not used extensively in the clinic

  11. Outline • Nitrogenous Bases • The Pentoses of Nucleotides and NA • Nucleosides are Formed by Joining a Nitrogenous Base to a Sugar • Nucleotides - Nucleoside Phosphates • Nucleic Acids are Polynucleotides • Primary Structure of Nucleic Acids • ABZs of DNA Secondary Structure • Denaturation and Renaturation of DNA • Secondary and Tertiary Structure of RNA

  12. Pentoses of Nucleotides Know these structures too • D-ribose (in RNA) • 2-deoxy-D-ribose (in DNA) • The difference - 2'-OH vs 2'-H • This difference affects secondary structure and stability

  13. Nitrogenous Bases Know the basic structures • Pyrimidines • Cytosine (DNA, RNA) • Uracil (RNA) • Thymine (DNA) • Purines • Adenine (DNA, RNA) • Guanine (DNA, RNA)

  14. Properties of Pyrimidines and Purines • Strong absorbance of UV light

  15. Nucleosides Linkage of a base to a sugar • Base is linked via a glycosidic bond

  16. （2） （1）

  17. (ψ) （3）

  18. Nucleotides Nucleoside phosphates • Know the nomenclature • "Nucleotide phosphate" is redundant! • Most nucleotides are ribonucleotides

  19. Functions of Nucleotides • Nucleoside 5'-triphosphates are carriers of energy • Bases serve as recognition units • Cyclic nucleotides are signal molecules and regulators of cellular metabolism and reproduction • ATP is central to energy metabolism • GTP drives protein synthesis • CTP drives lipid synthesis • UTP drives carbohydrate metabolism

  20. Nucleic Acids - Polynucleotides • Polymers linked 3' to 5' by phosphodiester bridges • Ribonucleic acid and deoxyribonucleic acid • Know the shorthand notations • Sequence is always read 5' to 3' • In terms of genetic information, this corresponds to "N to C" in proteins

  21. The DNA Double Helix Stabilized by hydrogen bonds! • "Base pairs" arise from hydrogen bonds • Erwin Chargaff had the pairing data, but didn't understand its implications • Rosalind Franklin's X-ray fiber diffraction data was crucial • Francis Crick knew it was a helix • James Watson figured out the H-bonds

  22. The Structure of DNA An antiparallel double helix • Diameter of 2 nm • Length of 1.6 million nm (E. coli) • Compact and folded (E. coli cell is only 2000 nm long) • Eukaryotic DNA wrapped around histone proteins to form nucleosomes • Base pairs: A-T, G-C

  23. Sec/Tert Structure of RNA Transfer RNA • Extensive H-bonding creates four double helical domains, three capped by loops, one by a stem • Only one tRNA structure (alone) is known • Phenylalanine tRNA is "L-shaped" • Many non-canonical base pairs found in tRNA

  24. Denaturation AND Renaturation of DNA • When double DNA molecules are subjected to conditions of pH, temperature or ionic strength that disrupt hydrogen bonds, the strands are no longer held together. The double helix is denatured. • If the temperature is the denaturing agent, the double helix is said to melt; • The phenomenon that the relative absorbance of the DNA solution at 260 nm increases as the bases unstack is called hyperchromic shift; • If one fellows the absorbance as a function of temperature, the midpoint temperature of the absorbance curve is termed melting temperature, Tm.

  25. Chain Termination Method Based on DNA polymerase reaction • Run four separate reactions • Each reaction mixture contains dATP, dGTP, dCTP and dTTP, one of which is P-32-labelled • Each reaction also contains a small amount of one dideoxynucleotide: either ddATP, ddGTP, ddCTP or ddTTP

  26. Lipid Metabolism

  27. 酶合成的阻遏作用

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