Protein Synthesis

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Protein Synthesis

• Transfer of the information of DNA into amino
  acids
• Transcription
• DNA template used to synthesize RNA
• Single stranded
• mRNA, rRNA and tRNA
• Translation
• Message of RNA used to generate amino acid chain
• Primary protein structure
• Requires cooperation of all three forms of RNA

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• Transcription
• Enzymes break DNA strands apart at specific sites
• Only one DNA strand serves as a template
• Information stored in sequence of DNA nucleotides
  is rewritten into RNA nucleotide sequence
• RNA is only formed in the 5 to 3 direction
• Nucleotides can only be added to the free 3 end
• RNA polymerase binds to DNA at promoter site and
  adds complementary bases
• RNA synthesis continues until a terminator is
  reached

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• Takes place in the cytoplasm of prokaryotic cells
  and the nucleus of eukaryotic cells
• nucleolus
• Eukaryotic DNA is more complex
• Exons
• regions of DNA that code for proteins
• Introns
• non-coding regions that separate exons
• Ribozymes removes the introns from mRNA
• RNA enzymes

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• Translation
• Rewrites the message of RNA into the language of
  proteins
• mRNA molecule consists of a series of codons
• Three base sequence that code for specific amino
  acids
• tRNA is the interpreter
• transfers amino acids from the cytoplasms amino
  acid pool to a ribosome
• Ribosomes are made of rRNA and proteins

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• tRNA molecule arrives at a ribosome with a
  specific amino acid at one end and an anticodon
  on the other
• pairs with the complementary codon on mRNA
• 64 codons (61 sense 3 non-sense)
• Some tRNAs have anticodons that can recognize two
  or more different codons
• Translation starts at a start codon (AUG) and
  releases the finished protein at a stop codon
  (UAA, UGA, or UAG)

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The structure of a tRNA molecule fits its
function
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Translation
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• In a prokaryotic cell, many molecules of mRNA can
  by transcribed simultaneously
• Why can translation begin before transcription
  has been completed in a prokaryote but not in a
  eukaryote?