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Chapter 21

Chapter 21. Nucleic Acids. Queen Victoria. Hemophilia. Goals. Describe nucleotides, RNA and DNA, polypeptides Know the 3D structure of nucleic acids Describe mutations and their effects Describe viruses and Recombinant DNA technology. Chromosomes. Humans have 46 Germ cells have 23

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Chapter 21

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  1. Chapter 21 Nucleic Acids

  2. Queen Victoria • Hemophilia

  3. Goals • Describe nucleotides, RNA and DNA, polypeptides • Know the 3D structure of nucleic acids • Describe mutations and their effects • Describe viruses and Recombinant DNA technology

  4. Chromosomes • Humans have 46 • Germ cells have 23 • Contain all genetic information of the organism

  5. RNA • Leave nucleus

  6. Nucleotides • Monomers that make up DNA and RNA

  7. Nucleotides • Made from

  8. Naming • Sugar and base • Adenine + sugar = • Cytosine + sugar = • is second part of the name • dGMP

  9. 5’ – 3’ Phosphodiester • In making DNA – • This is the direction used for naming

  10. DNA Structure • Watson and Crick 1953 • Complementary pairs

  11. Complementary Strands • Bases located • Maximum • Maximum • Hydrophobic bonds to the bases above and below

  12. Given… • G A T T A C A • What is the complementary strand?

  13. Size of DNA • 3x109 base pairs • Organized around • Around 200 base pairs/

  14. RNA • Single strand • Different types

  15. RNA Pairing • Only about ½ molecules base pair • Acceptor stem: • Anticodon -

  16. Information flow • Replication: • Transcription: • Translation:

  17. Replication • Copy all 46 chromosomes in less than a day (about 8 hrs) • Error – • Always in 5’  3’ direction and two strands grow opposite • DNA

  18. DNA Polymerase • “Checks” the accuracy of the pairing and correcting errors

  19. Practice • What is the corresponding daughter strand to the parent

  20. Transcription • Transcription bubble • RNA Polymerase acts on the template strand only • There is a start site • There is a termination site

  21. RNA Polymerase • No proofreading function • Error • Initial RNA is called primary transcript RNA, ptRNA • Later modified to the other types

  22. What RNA is formed? • If the DNA sequence is: • What is the RNA that is synthesized?

  23. Post transcription • End capping • Base modification • Splicing

  24. Translation • Protein synthesis • Sequence of bases specifies amino acid sequence • 64 codons for 20 amino acids

  25. Translation • Each tRNA carries ONLY ONE aa • Aminoacyl-tRNA synthetase • Peptidyl transferase • Synthesis terminates when STOP codon is reached

  26. Posttranslational Processing • Most lose • Folding begins • Disulfide-bridging • Quaternary structures assembled

  27. Control at every step • Not every cell expresses every gene • Specialized • Repressor proteins • Inducer proteins

  28. Mutations • Error in base sequence • Substitution (point) mutations • Frameshift mutations

  29. Spontaneous Mutations and Mutagens • Spontaneous mutations • Sodium nitrite • In processed meats • Converts cytosine to uracil • Overall danger thought to be low • Reduces occurrence of botulism

  30. Spontaneous Mutations and Mutagens • Benzopyrene • Found in car exhaust, tobacco smoke, burnt meats • Radiation

  31. Silent Mutations • Base-sequence errors that don’t affect organism • 64 codons for 20 amino acids • Change may be in unimportant region • Genes have 2 or more copies

  32. Mutations • Somatic cells • Germ cells

  33. Antibiotics • Chemicals to fight infection • Block protein synthesis • Must finish whole course • Bacteria • Antibiotic resistant bacteria

  34. Viruses • DNA or RNA with protein coat • No functions outside cell • Enter cell and “hijack” it • Each virus attacks only specific cells • TMV • AIDS

  35. DNA Viruses • Enter host cell and nucleus • Insert themselves into • Hiding inside cell – hard for immune system to detect • Can stay indefinitely

  36. RNA Viruses • Enters cell • Directs synthesis of • Uses machinery of host to make copies of itself

  37. Retroviruses • Special RNA virus • Enters cell and directs synthesis of viral DNA using reverse transcriptase • DNA inserts into host genome • Can hide or remain dormant for long periods of time • HIV

  38. Treatment • Antibiotics don’t work • Body doesn’t recognize virus once hiding in host cell • Best method:

  39. Recombinant DNA Technology • Began in mid-70s • Transplanting or altering of DNA • Benefits • Therapeutic drugs • Improvements to crops and herds • Curing/treating of genetic diseases

  40. Production of human insulin • First application of recombinant DNA technology • Uses yeast and bacteria as vehicle • Bacteria have genomic DNA and a plasmid • Less side effects than cow or pig insulin

  41. Process Identify gene encoding wanted protein • Isolate this gene from the donor DNA • Splice into plasmid (vector DNA) • Restriction enzymes • Recombinant DNA (new plasmid) back into E. coli • Chemical shock • Heat shock

  42. Other techniques • Microinjections • Direct injection of DNA into nucleus of another cell • Cloning ~~~ Dolly • Viral vectors • Altered virus (usually retrovirus) • Carries new DNA to host cell • Research now for cystic fibrosis

  43. A Little More About Cloning • Enucleation of cell: • http://gslc.genetics.utah.edu/units/cloning/whatiscloning/images/enucleation.mpg • Nuclear Transfer: • http://gslc.genetics.utah.edu/units/cloning/whatiscloning/images/transfer.mpg • Cloning “Practice”: • http://gslc.genetics.utah.edu/units/cloning/clickandclone/

  44. Transgenic Breeding • Organisms with altered DNA • Grow faster, larger, etc. • Resistant to pests • http://www.pbs.org/wgbh/harvest/engineer/transgen.html • Many already in your supermarket

  45. Gene Therapy • Human Genome Project • Finished with sequence • Now identify genes and proteins • Insert correct gene for defective one • Modified adenovirus (common cold) • Aerosol spray inhaled • Injection into bloodstream • Incubation of cells

  46. Ethical Considerations • Effects of recombinant DNA? • Can we test people for diseases? • Alzheimer’s; Huntington’s • Gene Therapy • Enhance intelligence, strength • Pick eye color • Who will benefit? Will anyone suffer?

  47. Internet Sites of Interest • PBS Site about GMOs • http://www.pbs.org/wgbh/harvest/ • Genetic Science Learning Center • http://www.pbs.org/wgbh/harvest/ • NWABR • http://www.nwabr.org

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