AP Biology - DNA and RNA

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  • 1. Chapters 16
    DNA Structure and Replication
  • 2. DNA = ?
    TH Morgan: “genes are located on chromosomes”
    Is protein or DNA the genetic material?
    “PROTEIN!” (Why?)
  • 3. Frederick Griffith’s Experiments
  • 4. Griffith’s Results
    Transformation: uptake of external DNA
    Descendants of transformed bacteria were virulent
  • 5. Hershey-Chase Experiments
  • 6. DNA
    Chargaff’s Rules:
    Found similarities in percentages of various bases
    A: 30.3%
    T: 30.3 %
    C: 19.9%
    G: 19.6%
    Watson and Crick, double helix: 1953
  • 7. Structure of DNA
    Nucleotide = sugar + Phosphate + base
    Sugar (3’ end) / phosphate (5’ end) make up anti-parallel “backbone”
    A/G: purines (2-ringed)
    C/T: pyrimidines (1-ringed)
  • 8. Structure of DNA
    Purine-purine and pyrimidine-pyrimidine pairing results in a variable diameter
    Full helical turn: 3.4 nm
    Base pair width: .34 nm
    1 nm = .000000001 m
  • 9. DNA Replication
    Can you ID the matching strand? YES!
    Semiconservative replication: each parental strand serves as a template
  • 10. DNA Replication
    12,000,000,000 bases to be replicated in only a few hours – wow!
    Catalyzed by DNA polymerase
    Terms: origins, replication forks
  • 11. DNA Elongation
    DNA polymerases use nucleoside triphosphates to elongate strand
    New DNA elongates only at 3’ end
    Leading strand (continuous) / lagging strand (fragmented)
  • 12. DNA Elongation
    Okazaki fragments 100-200 nucleotides long
    DNA ligase joins fragments eventually
  • 13. Priming DNA Synthesis
    Primases create a 5-10 nucleotide RNA primer
    Each Okazaki fragment (lagging strand) as well as the leading strand must be primed
    DNA polymerase I replaces RNA nucleotides with DNA
  • 14.
  • 15. Other Enzymes
    Helicase and topoisomerase “untwist” DNA
  • 16.
  • 17. Proofreading DNA
    Polymerases proofread as they synthesize
    Nucleases “cut out” mismatched base pairs (“nucleotide excision repair”)
  • 18. Telomeres
    Repeated “TTAAGG” at 3’ end (1000x)
    Telomerase functions in germ cells
    When would it be good to limit # of cell reproductions?
  • 19. Chapter 17
    Translation and Transcription
  • 20. One Gene-One Polypeptide Hypothesis
    Transcription: DNA  mRNA
    Translation: RNA  polypeptide at ribosome
    Benefits: protection for DNA, multiple RNA molecules made
  • 21. RNA
    Ribose sugar
    Single stranded
    Does not remain in nucleus
    Contains uracil base
    3 types
  • 22. Codons
    Each amino acid coded for by set of three bases
    Why are 3 needed?
  • 23. The DNA/RNA Code
    DNA: 3’ – A C C A AA C C G A G T – 5’
    RNA: 5’ – U G G U UU G G C U C A – 3’
    Polypep. TrpPheGly Ser
  • 24. mRNA Synthesis
    RNA polymerase synthesizes mRNA 5’  3’
    No primer
    Sections of genes start with a promoter, end with terminator
    Initiated by transcription factors (eukaryotes)
  • 25. mRNA Synthesis
    Untranslated regions also synthesized
    In eukaryotes, pre-mRNA is cut as RNA polymerase continues to function
    RNA processing creates finished mRNA
  • 26. RNA Processing
    5’ end gets a “cap” (modified G nucleotide)
    3’ gets poly-A tail
    Functions:
    mRNA exporting
    Protection from breakdown
    Ribosome attachment
  • 27. RNA Splicing
    On average, 80% of RNA must be removed
    Noncodingintrons between coding sections (exons)
    Small nuclear ribonucleoproteins (snRNPs) form spliceosomes
  • 28. Ribozymes
    RNA acts as an enzyme
  • 29. Why are introns important?
    Relatively small number of genes because of alternative RNA splicing
    Different exons – different protein domains
    Longer chromosomes = more crossing over
  • 30. Transfer RNA in Translation
    Transfers amino acids to ribosome
    Structure important
    Anticodon (opposite of RNA code)
    “translator” molecule
  • 31. Transfer RNA in Translation
    1 of 20 aminoacyl-tRNA-synthetases binds tRNA to amino acid
    “Wobble” explains similarities in third base
  • 32. Ribosomes
    2 subunits
    rRNA and protein
    3 sites: P, A, and E
  • 33. Translation: Initiation
    Small subunit “scans” for start codon
    Start codon of mRNA binds to initiator tRNA and ribosome
    Requires: initiation factors (proteins) and GTP for energy
  • 34. Translation: Elongation
    mRNA moves 5’ end first
    Codon recognized
    Amino acid joined to chain by peptide bond
    tRNA exits as ribosome awaits next one
    Requires GTP (energy)
  • 35. Translation: Termination
    Stop codon: mRNA accepts release factor protein
    Polypeptide released; ribosome dissociates
  • 36. Ribosome Efficiency
    Polyribosomes allow multiple polypeptides from one strand of mRNA
    Bonding of signal recognition particles allow for synthesis of polypeptide within E.R.
  • 37. Importance/Function of RNA
    Hydrogen bond to other DNA/RNA
    Fold into a 3D shape
    Can act as catalyst (ribozyme)
  • 38. Mutations
    “point mutations” change a single base pair
    Base-pair substitution
    Insertion
    Deletion
    Missense mutation
    Nonsense mutation
    Frameshift mutation
  • 39. In Review,
    A gene is “a region of DNA whose final product is a polypeptide or RNA molecule