protein synthesis

• Protein synthesis


  The process where proteins are made
• Protein synthesis


  1. Transcription (in the nucleus)

  2. Translation (in the cytoplasm)
• Transcription


  The first step where a copy of the gene of interest on DNA is made into mRNA
• Transcription


  • DNA is too big to leave the nucleus, so a copy is made in the form of mRNA
  • mRNA is a much shorter molecule than DNA, so it can move through the nuclear pores into the cytoplasm
• Transcription


  1. DNA double helix unwinds

  2. One DNA strand acts as a template

  3. RNA nucleotides align complementarily and are joined by RNA polymerase

  4. Pre-mRNA is formed

  5. Introns are spliced out by spliceosome, leaving only exons
• Introns


  Sequences of bases in DNA that do not code for amino acids
• Exons


  Coding regions of DNA
• Translation


  The second step where the polypeptide chain (primary structure of a protein) is created using mRNA and tRNA
• Translation


  1. mRNA attaches to ribosome at start codon

  2. tRNA molecules bring specific amino acids to match codons on mRNA

  3. Ribosome holds mRNA and tRNA in place

  4. Peptide bonds form between amino acids

  5. Ribosome moves along mRNA, adding amino acids

  6. Translation stops at stop codon
• Start codon


  First three mRNA bases that mark the beginning of the coding sequence
• Stop codon


  Last three mRNA bases that do not code for an amino acid and cause the ribosome to detach
• Protein synthesis requires energy (ATP) to form peptide bonds
• The final 3D shape of the protein is determined by further modifications in the Golgi body