Cards (6)

  • 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