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Chapter 12 Nucleic Acids

Chapter 12 Nucleic Acids. A. Nucleic Acids Macromolecules composed of subunits called nucleotides  polymers made of monomers Nucleotides :“ building blocks ” for DNA (deoxyribonucleic acid) & RNA (ribonucleic acid). Cont. Nucleotides. Based on sugar (2 general types of nucleotides)

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Chapter 12 Nucleic Acids

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  1. Chapter 12Nucleic Acids

  2. A. Nucleic Acids • Macromolecules composed of subunits called nucleotidespolymers made of monomers • Nucleotides:“building blocks” for DNA (deoxyribonucleic acid) & RNA (ribonucleic acid)

  3. Cont. Nucleotides • Based on sugar (2 general types of nucleotides) a. Ribotides ribose nucleotides b. Deoxyribotidesdeoxyribose nucleotides

  4. Cont. Nucleotides • Nucleotides composed of 3 subunits: a. Pentose sugar (C5) RNA: ribose (R) DNA: deoxyribose (D)

  5. Cont. Nucleotides b. Phosphate group (H2PO3) • Derived from phosphoric acid (H2PO3 - inorganic compound) c. Nitrogen base • DNA: adenine (A) , cytosine (C), guanine (G), thymine (T) • RNA: adenine, cytosine, guanine, uracil (U)

  6. c. Nitrogen bases are 1 of 2 types: • Pyrimidine- C, T, U (consist of single-ring) • Purines- A, G (consist of double-ring) Cytosine Thymine Uracil Adenine Guanine

  7. B. Ribose and DNA Nucleotides *** NOTE: Uracil only in ribose series; thymine only in deoxyriboseseries!!!

  8. C. Nucleotides can be synthesized into: 1. Energy carriers ATP, CTP, GTP, TTP, UTP 2. Coenzymes(carry H2) FMN (Flavin Mononucleotide) FAD (Flavin Adenine Dinucleotide) NAD (Nicotinamide Adenine Diphosphate) NADP (Nicotinamide Adenine DinucleotidePhosphate) 3. Genetic Systemspolymers called DNA & RNA

  9. DNA Nucleotides A-T or A-U (2 H-bonds) G-C (3 H-bonds)

  10. D. DNA(Watson-Crick Model); proposed 1953 1. Genetic material composed of 2 long chains of nucleotides 2. A=T ; C=G (*base pairs rulepyrimidinealways pairs with purine 3. 2 chains run in opposite directions, connected by nitrogen bases to form double helix. 4. Hydrogen bonds between bases

  11. Cont. DNA (Watson-Crick Model) 5. DNA forms genes genetic information that passes from parent to offspring

  12. E. RNA(essential to protein synthesis) 1. Contains ribose instead ofdeoxyribose 2. Contains uracil instead of thymine 3. Nucleotides in long chains, in single strands unless RNA is the only nucleic present in the organism 4. THREE types of RNA: a. messenger RNA (mRNA) b. transfer RNA(tRNA) Essential in protein synthesis! c. ribosomal RNA (rRNA)

  13. RNA vs DNA

  14. Chapter 12: DNA Replication ***RECAP: DNA replication occurs in S phase of cell cycle A. DNA Structure 1. Double-stranded polymer composed of paired nucleotides 2. Because A combines with T, C with G, SEQUENCE of bases varies to produce different genes 3. Once nucleotide sequence is fixed, sequence in other strand is also determined

  15. B. DNA Replication (S phase) 1. Requires a team of enzymes (DNA polymerase) 2. Steps in replication: a. One enzyme unwinds portion of DNA b. Another enzyme breaks H-bonds between paired nucleotides and separates strands c. New nucleotides are added to each original strand in proper direction according to original strand d. Phospatesof new nucleotides bond to sugars e. New strand attached to original

  16. DNA Replication

  17. Cont. DNA Replication 3. SemiconservativeReplication (validated!) each new DNA molecule contains ½ of original

  18. Cont. DNA Replication 4. Conservative Replication (negated) one DNA molecule = 2 “old” strands one DNA molecule = 2 “new” strands 5. Each new cell formed after M phase (mitosis) in cell cycle contains same set of chromosomes & genes as parent cell (each DNA ½ old, ½ new)

  19. C. Replication Forks 1. DNA is a giant molecule! 2. If replication began at one end, process would take TOO LONG! 3. Replication forksmultiple sites of DNA replication

  20. Cont. Replication Fork 4. Replication different along each strand (done by DNA POLYMERASE!) a. Leading strandsynthesis continues in ONE direction • Nucleotides added one at a time- in order b. Lagging strand short, discontinuous segments of DNA synthesized • Segments then joined by DNA ligases 5. Result: Synthesis of 2 new DNA molecules behind the replication fork as it moves along original DNA molecule

  21. Chemical Evidence for Watson-Crick Model • Erwin Chargaff- analyzed nuclei of different cell types *** SIGNIFICANCE: The concentration of specific bases (A & T)/ (C & G) approached a 1:1 ratio  (A=T) and (C=G) Upon analysis of many tissues from many different species, Chargaff concludedthat the amounts of A & T and C & G were ALMOST EXACTLY EQUAL!

  22. Cont. Watson-Crick Model 2. Watson and Crick reasoned that these the 1:1 ratio was due to PAIR BONDING between the 2 bases that were equal (A-T) and (C-G) 3. Watson and Crick reasoned that these specific bases would bond according to SIZE always 1 pyrimidine paired with 1 purine • Size of these base pairings was proven experimentally by the x-ray diffraction work of Wilkins and Franklin 4. Watson and Crick used the 1:1 ratio of A-T and C-G to propose a mechanism of replication or making an exact copy of itself • Proposed in 1953 that the method of replication of DNA would be SEMI-CONSERVATIVE • Each new strand molecule retains ½ of the original DNA molecule

  23. Cont. Watson-Crick Model 5. Watson-Crick Model for the structure of DNA in 1953 revolutionized Biology a. Nature of the gene b. Explanation of mutations c. Variations w/in species sequence of nucleotides make specific types of genes d. Cell division and reproduction e. Abnormal cell divisioncancer

  24. Meselson- Stahl confirmed semi-conservative replication

  25. 1928- Griffith’s Transformation

  26. Avery, MacLeod, McCarty 1944- DNA was transforming agent

  27. 1952- Chase & Hershey’s Experiment

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