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Translation Steps

Page history last edited by Jay 13 years, 3 months ago

Making Proteins: Synthesis

TRANSCRIPTION

  1. DNA in nucleus
  2. RNA polymerase binds to promoter region on sense strand of DNA
  3. DNA strands unwind ahead of RNA polymerase & separate (break H bonds)
  4. [template is "antisense" strand]
  5. [RNA nucleotides float into position and match with DNA complements on the template]
  6. [RNA polmerase binds RNA nucleotides to each other in 5' -> 3' direction]
  7. [RNA stops building at end of gene sequence when it reaches "terminator"]
  8. RNA processing (to produce mature RNA):
    1. Introns are cut OUT of RNA sequence....
    2. Exons are re-attached together
    3. Cap and Tail are added to RNA
    4. mRNA released into cytoplasm from nucleus

 

TRANSLATION

general overview

    • Translation include initiation, elongation, termination
    • mRNA translated in 5' --> 3' direction
    • tRNA have an anticodon which is complementary to codon on mRNA -AND- they carry cooresponding amino acid.
    • in cytoplasm, special enzymes attach correct amino acid to each tRNA
      • this requires ATP
    • tRNA with appropriate amino acid attached is called "activated tRNA"
    • mRNA released into cytoplasm from nucleus 

 

Initiation

  1. initiating tRNA (carrying methionine) binds to small ribosomal subunit
  2. Small ribosomal subunit/tRNA complex binds to mRNA
  3. ... complex moves along mRNA until it reaches start codon (AUG) 
  4. large ribosomal subunit binds to small ribosomal subunit / mRNA /tRNA complex
  5. Ribosome has 2 working sites: P site and A site ; tRNA is in P-site 
  6. 2nd tRNA with antiocodon complementary to second codon, fits into A site  

 

 Elongation 

[occurs in 5' --> 3' direction]

  1. next tRNA complementary the next codon (and carries the amino acid for that codon) fits into the A site
  2. ribosome catalyzes peptide bond formation between two amino acids
    • this requires energy in form of GTP
  3. SIMULTANEOUSLY - the ribosome/mRNA shift so that the second tRNA shifts to P site.
  4. SIMULTANEOUSLY - the first tRNA shifted into E site
  5. SIMULTANEOUSLY - tRNA in E site releases the first amino acid (now bonded to amino acid on tRNA in the P site)
  6. SIMULTANEOUSLY - tRNA in E site is released from mRNA and leaves to recharge in cytoplasm 
  7. SIMULTANEOUSLY - the polypeptide coils up to form 3-D shape
  8. [SIMULTANEOUSLY - other ribosomes can be decoding the SAME mRNA!!!!]
  9. When STOP codon enters site 2, ribosome splits into its two subunits and drifts away.
  10. ie. the come in to riboStart codon of mRNA attracts anti-codon of tRNA

 

Termination

  1. next asdf
  2. as

 

 

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