RNA, DNA, and Protein Synthesis

1
RNA, DNA, and Protein Synthesis

• Daria Z. Hall
• Chem 504
• Biochemistry
• Dr. Thornton

2
Transcription

• DNA acts as a template for the creation of RNA
• Transcription factor protein that binds to DNA
  and helps regulate the formation of RNA
• These bind to a promoter site on the 5 end of
  the gene to be transcribed

3
Transcription

• Next, RNA polymerase binds to the transcription
  factor
• This complex forces open the DNA double helix

http//trc.ucdavis.edu/biosci10v/bis10v/week5/tran
scription.gif
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Transcription

• The RNA polymerase moves down the single strand
  of DNA in the 3 to 5 direction.
• As it moves along, it creates a strand of RNA by
  assembling ribonucleotides that are complementary
  to the DNA.

5
Transcription

• Complementary bases
• Follows similar rules to DNA replication
• G is read, C is placed
• C is read, G is placed
• T is read, A is placed
• BUT when A is read, U is placed

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Transcription

• Synthesis of RNA proceeds in 5 to 3 direction
• As the polymerase proceeds, the DNA helix reforms
  behind it
• When transcription is complete, the RNA
  polymerase releases the DNA

http//www.modares.ac.ir/elearning/mnaderi/Genetic
20Engineering20course20II/images/DNA3c.gif
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From Transcription to Translation

• Once the RNA has been synthesized from the DNA
  template, it is used for translation
• Translation is the synthesis of amino acids using
  the RNA formed via transcription as a template
• This occurs in the cytoplasm where the ribosomes
  are found

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Translation (Initiation)

• The small subunit of a ribosome binds to the DNA
  upstream (in the 5 direction) of the start of
  the protein coding section
• It moves from the 5 to the 3 direction until it
  sees the START codon (AUG)
• At this point, the large subunit of the ribosome
  also binds to the RNA
• A methionine tRNA (coded by AUG) also binds to
  the ribosome

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Translation (Initiation)
http//trc.ucdavis.edu/biosci10v/bis10v/week5/init
iation.gif
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Translation (Elongation)

• A tRNA coding for the next codon in line now
  comes in
• An elongation factor and GTP (energy source) are
  also required
• The new amino acid is linked to the preceding
  methionine by a peptide bond
• The initiator tRNA is released, and the ribosome
  moves one codon downstream

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Translation (Elongation)
http//trc.ucdavis.edu/biosci10v/bis10v/week5/elon
gation.gif
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Translation (Elongation)

• A new tRNA associated with the next codon comes
  in
• It also uses the elongation factor and GTP to
  link a new amino acid to the growing peptide
  chain by a peptide bond
• This process continues until the ribosome reaches
  a STOP codon

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Translation (Termination)

• The STOP codon is UAA, UAG, or UGA
• These codons are recognized by protein release
  factors
• The protein release factors cause the release of
  the polypeptide from the ribosome
• The ribosome splits back into its two subunits
  that can be recycled

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Translation (Termination)
http//kvhs.nbed.nb.ca/gallant/biology/translation
_termination.jpg
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Translation (Overall)
http//nobelprize.org/educational_games/medicine/d
na/a/translation/index.html
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Protein Synthesis (Overall)
http//stemcells.nih.gov/StaticResources/info/scir
eport/images/figurea6.jpg