protein synthesis

• messenger RNA:

  • used to transfer DNA code from the nucleus to the ribosome (transcription)
  • single stranded
  • ribose sugar
  • contains uracil instead of thymine
  • built up by the complementary bases pairing of DNA strand
• transfer RNA:

  • used to decode the mRNA sequence into a protein (translation)
  • small molecule (approx 80 nucleotides)
  • single stranded, clover leaf shaped with one end slightly longer that can attach to an amino acid
  • anti codon = 3 bases that pair with the complementary codon on mRNA
• transcription:

  1. helicase breaks down the hydrogen bonds between the bases on a section of DNA
  2. RNA polymerase moves along the template DNA (antisense strand - 3' to 5')
  3. free nucleotides join up with the complementary bases on the antisense strand
  4. C - G, G - C, A - U, T - A
  5. RNA polymerase forms the phosphodiester bonds between the nucleotides
  6. when a stop codon is reached, the chain is terminated and the mRNA strand moves out of the nucleus via nuclear pore
• translation:

  1. mRNA attaches to the start codon on the ribosome
  2. tRNA with a complementary anti codon attaches to the mRNA
  3. another tRNA anticodon binds to the next mRNA
  4. the amino acids on the tRNA molecule are joined by a peptide bond
  5. the ribosome moves along the mRNA strand, releasing the first tRNA
  6. another tRNA is added and the process continues until a stop codon is reached
  7. a polypeptide is released which forms the primary protein structure
• start codon - AUG (methionine)
• stop codons = UAA, UGA or UAG