Protein synthesis

• draw and label a tRNA molecule

  
• Transcription: Step 1


  RNA polymerase attaches to the DNA helix at the start of a gene
• Transcription: Step 2


  DNA helicase attached to the RNA polymerase hydrolyses the hydrogen bonds between bases on the DNA molecule, exposing the bases
• Transcription: Step 3


  One of the DNA strands is used as a template
• Transcription: Step 4


  RNA polymerase lines up free RNA nucleotides alongside the exposed bases, forming a complimentary copy of the DNA template
• Transcription: Step 5


  RNA polymerase moves along the strand, joining the free nucleotides with phosphodiester bonds to form mRNA
• Transcription: Step 6


  Hydrogen bonds reform between the uncoiled DNA strand as the RNA polymerase passes by
• Transcription: Step 7


  When RNA polymerase reaches a stop codon, it disassociates and the mRNA is released
• Transcription: Step 8


  mRNA moves out of the nucleus via nuclear pore and attaches to a ribosome
• splicing


  the process of removing introns and reconnecting exons in a pre-mRNA to form mRNA
• in what organisms does splicing occur

  eukryotes
• why does splicing not happen in prokaryotes

  Prokaryotic DNA does not contain introns
• Translation Step 1


  mRNA attaches itself to a ribosome and tRNA carries amino acids to it
• Translation Step 2


  tRNA with the anticodon complementary to the first codon on the mRNA attaches itself to the mRNA
• Translation Step 3


  Second tRNA attaches itself to the next codon in the same way
• Translation Step 4


  The two amino acids on the tRNA molecules are joined by a peptide bond
• Translation Step 5


  The first tRNA molecule moves away leaving its amino acid behind
• Translation Step 6


  A third tRNA binds and its amino acid joins the peptide chain, then the second tRNA moves away
• Translation Step 7


  Translation continues until a stop codon is reached
• Translation Step 8


  The polypeptide chain is released