CEN 551

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Central Dogma Movie(A0042201)
DNA Movie(A0002902)
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REPLICATION
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5 and 3 Ends of DNA
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Replication- Making New DNA

• Enzymes break hydrogen bonds between DNA strands
• DNA strands separate
• RNA primer added at initiation site to start
  DNA synthesis
• primer is small piece of RNA that is
  complimentary to a specific section of DNA and
  will bind to that section of DNA
• DNA synthesized by enzyme DNA polymerase

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• nucleotides of DNA always added to terminal 3
  group
• Leading strand synthesized continuously
• DNA polymerase must jump ahead and work backward
  on lagging strand
• DNA fragments on lagging strand are called
  Okazaki fragments
• Fragments joined by an enzyme called DNA ligase

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DNA Replication
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Replication is Semi-conservative
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EM photo of E. coli DNA Replication
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DNA Replication Movie(A0002701)
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TRANSCRIPTION
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Transcription RNA Synthesis

• Necessary parts of DNA become unbound
• One strand is the template for each gene.
• Definition of a gene encodes for one protein
• RNA polymerase reads DNA and synthesizes mRNA
• RNA polymerase consists two parts core and sigma
  subunit

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Transcription (continued)

• Three steps Initiation, elongation, termination
• An operon (in procaryotes) consists of a
  promoter, genes, and a terminator
• Initiation begins with binding of sigma factor to
  promoter region of DNA

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Transcription (continued)

• Promoters vary in binding affinity for the sigma
  factor
• When the sigma factor is released, elongation
  begins
• MRNA synthesis stops when RNA polymerase
  encounters a terminator (specific sequence of
  bases) (can vary in strength also)

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Transcription (continued)

• Procaryotic transcription can be polygenic
  (multiple genes controlled by one promoter)
• In procaryotes, transcription and translation
  occur simultaneously.
• mRNA in eucaryotes can have nonsense segments,
  called introns
• Introns make it more difficult to transfer
  eucaryotic genes to procaryotes

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RNA Post Processing (Eucaryotes)
exon intron exon
intron degraded before translation
mRNA rejoined
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Eucaryotic mRNA Processing Movie(A0158701)
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Transcription Movie(A0001001)
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TRANSLATION
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Translation Making Protein

• Three steps again Initiation, elongation,
  termination
• In procaryotes, initiation is the formation of a
  30s and 50s rRNA initiation complex.
• rRNA means ribosomal RNA, 30s and 50s are the
  sizes of two parts of the ribosome
• Elongation uses tRNA with attached amino acids
• Three letter words of four possible letters
  (U,C,A,G) form codons on mRNA (64 possible,
  many redundant)
• anti-codons on tRNA match the codons on mRNA

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tRNA Structure
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Code for Protein Synthesis
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Translation (continued)

• Three codons (UAA, UAG, and UGA) do not code for
  amino acids and are stop codons. Translation
  stop, or translation terminations sequence.
• Translation start codon is AUG.
• Two sites on the ribosome for the tRNA called P
  and A

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Translation Movie (A0001404)
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Posttranslational Processing

• Folding chaperones (proteins) that assist in
  folding.
• Secretion signal sequence a sequence of 20-25
  amino acids on the front of a protein that
  directs the protein to be secreted out of the
  cell. The signal sequence is clipped off during
  secretion.
• Glycosylation addition of sugars to the protein
  structure.

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Secretion

• Procaryotes secretion through the cytoplasmic
  membrane.
• Eurcaryotes transport vesicles bud around the
  proteins and transport to the membranes.

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Three main mechanisms by which membrane-bounded
organelles import proteins. The protein remains
folded during the transport steps in mechanisms 1
and 3 but usually has to be unfolded in mechanism
2. All of these processes require energy.
http//www.accessexcellence.org/AB/GG/Anchor-Cell
-33869
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Glycosylation

• N-linked glycosylation is only accomplished in
  eucaryotic organisms.
• Glycosylation pattern is a target for the body to
  clear (remove) proteins. Non-native
  glycosylation patterns will be removed. Critical
  implications for producing therapeutic proteins
  for human injection.