Molecular genetics

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Molecular genetics

• Chromosomes carry genes
• Hershey and Chase showed the DNA was the genetic
  material and not proteins
• - phage lab
• Watson and Crick showed the structure of DNA

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Structure of DNA

• Watson and Crick showed
• Double helix

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Base pairs

• Purines and pyrimidines
• Adenine and guanine are purines
• Cytosine and thymine are pyrimidines
• In DNA, Adenine pairs with Thymine (A and T)
• Cytosine pairs with Guanine (C and G)

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Why does a purine have to pair with a pyrimidine?
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Antiparallel

• Remember where the 5 and 3 names come from?
• 5 end is the end where the phosphate group is
  exposed it is coming off of the 5th carbon
• 3 end is the end where the hydroxyl group is
  exposed it is coming off of the 3rd carbon

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DNA replication

• Semiconservative
• At the end of replication, the new DNA consists
  of one original daughter strand

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DNA Replication

• Six major points
• 1. Starts at points of origin

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DNA Replication

• Initiation proteins bind to the points of origin
  and form a replication bubble. Replication then
  begins in both directions from 5 to 3

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DNA Replication

• 3. DNA polymerases elongate the DNA from the
  replication fork out

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DNA Replication

• 4. DNA polymerase works from 5 to 3 on the new
  strand adding complimetary bases one at a time

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DNA Replication

• 5. Remember that the strands are antiparallel
  leading strand and lagging strand

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DNA Replication

• 6. Lagging strand a series of Okazaki
  fragments that are sealed together with DNA ligase

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Accuracy of replication

• Base pairing
• Mismatch repair enzymes fix incorrectly paired
  nucleotides
• Nucleotide excision repair wrong ones cut out
  with nucleases and the remaining gap is filled

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Chromosomes

• Bacterial vs. eukaryotic
• Bacterial one double stranded, circular DNA
  molecule with small amts of protein
• Eukaryotic linear DNA associated with large
  amounts of protein

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Chromosome packing

• DNA wrapped around histones nucleosome
• String of nucleosome folds
• Further folding forms a looped domain

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Gene to Protein

• Transcription
• - reading (transcribing) DNA to make messenger
  RNA
• - occurs in the nucleus
• Eukaryotics
• - transcription makes pre-mRNA modified to
  mRNA
• Prokaryotics directly makes mRNA

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Steps to transcription

• Initiation
• - DNA sequence where the RNA polymerase binds to
  is called the promoter
• - DNA sequence where the RNA polymerase stops
  transcribing is called the terminator
• RNA polymerase and transcription factors bind to
  the promoter in eukaryotic cells (bacteria do not
  need the transcription factors)

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Steps to transcription

• Elongation
• -RNA polymerase moves along the DNA untwisting
  the double helix and adding RNA nucleotides to
  the 3 end
• - as it reads DNA and moves on, the DNA rewinds

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DNA Transcription

• Termination
• - hits the terminator sequence
• - RNA transcript is released
• - polymerase detaches

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Processing RNA after transcription

• In eukaryotes, there are key post transcription
  modifications to RNA
• Addition of a 5 cap
• Addition of a poly-A tail
• These help the export of the mRNA form the
  nucleus, protect it from enzymes, and help
  attachment to the ribosome

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Processing RNA after transcription

• In addition to the 5 cap and poly-A tail,
  splicing occurs
• Introns are cut out
• Exons are left and spliced together by spliceosome

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Other types of RNA

• In addition to mRNA, there are two other primary
  types of RNA used in protein synthesis
• Transfer RNA (tRNA)
• Ribosomal RNA (rRNA)