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AP Biology - DNA and RNA
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AP Biology - DNA and RNA

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    AP Biology - DNA and RNA AP Biology - DNA and RNA Presentation Transcript

    • Chapters 16
      DNA Structure and Replication
    • DNA = ?
      TH Morgan: “genes are located on chromosomes”
      Is protein or DNA the genetic material?
      “PROTEIN!” (Why?)
    • Frederick Griffith’s Experiments
    • Griffith’s Results
      Transformation: uptake of external DNA
      Descendants of transformed bacteria were virulent
    • Hershey-Chase Experiments
    • 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
    • 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)
    • 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
    • DNA Replication
      Can you ID the matching strand? YES!
      Semiconservative replication: each parental strand serves as a template
    • DNA Replication
      12,000,000,000 bases to be replicated in only a few hours – wow!
      Catalyzed by DNA polymerase
      Terms: origins, replication forks
    • DNA Elongation
      DNA polymerases use nucleoside triphosphates to elongate strand
      New DNA elongates only at 3’ end
      Leading strand (continuous) / lagging strand (fragmented)
    • DNA Elongation
      Okazaki fragments 100-200 nucleotides long
      DNA ligase joins fragments eventually
    • 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
    • Other Enzymes
      Helicase and topoisomerase “untwist” DNA
    • Proofreading DNA
      Polymerases proofread as they synthesize
      Nucleases “cut out” mismatched base pairs (“nucleotide excision repair”)
    • Telomeres
      Repeated “TTAAGG” at 3’ end (1000x)
      Telomerase functions in germ cells
      When would it be good to limit # of cell reproductions?
    • Chapter 17
      Translation and Transcription
    • One Gene-One Polypeptide Hypothesis
      Transcription: DNA  mRNA
      Translation: RNA  polypeptide at ribosome
      Benefits: protection for DNA, multiple RNA molecules made
    • RNA
      Ribose sugar
      Single stranded
      Does not remain in nucleus
      Contains uracil base
      3 types
    • Codons
      Each amino acid coded for by set of three bases
      Why are 3 needed?
    • 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
    • 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)
    • mRNA Synthesis
      Untranslated regions also synthesized
      In eukaryotes, pre-mRNA is cut as RNA polymerase continues to function
      RNA processing creates finished mRNA
    • RNA Processing
      5’ end gets a “cap” (modified G nucleotide)
      3’ gets poly-A tail
      Functions:
      mRNA exporting
      Protection from breakdown
      Ribosome attachment
    • RNA Splicing
      On average, 80% of RNA must be removed
      Noncodingintrons between coding sections (exons)
      Small nuclear ribonucleoproteins (snRNPs) form spliceosomes
    • Ribozymes
      RNA acts as an enzyme
    • Why are introns important?
      Relatively small number of genes because of alternative RNA splicing
      Different exons – different protein domains
      Longer chromosomes = more crossing over
    • Transfer RNA in Translation
      Transfers amino acids to ribosome
      Structure important
      Anticodon (opposite of RNA code)
      “translator” molecule
    • Transfer RNA in Translation
      1 of 20 aminoacyl-tRNA-synthetases binds tRNA to amino acid
      “Wobble” explains similarities in third base
    • Ribosomes
      2 subunits
      rRNA and protein
      3 sites: P, A, and E
    • 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
    • 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)
    • Translation: Termination
      Stop codon: mRNA accepts release factor protein
      Polypeptide released; ribosome dissociates
    • Ribosome Efficiency
      Polyribosomes allow multiple polypeptides from one strand of mRNA
      Bonding of signal recognition particles allow for synthesis of polypeptide within E.R.
    • Importance/Function of RNA
      Hydrogen bond to other DNA/RNA
      Fold into a 3D shape
      Can act as catalyst (ribozyme)
    • Mutations
      “point mutations” change a single base pair
      Base-pair substitution
      Insertion
      Deletion
      Missense mutation
      Nonsense mutation
      Frameshift mutation
    • In Review,
      A gene is “a region of DNA whose final product is a polypeptide or RNA molecule