Transcription & Translation

Transcription DNA  mRNA (occurs in the nucleus) RNA polymerase binds to & separates the DNA strands at promoter sites Promoter - 3 base sequence that serves as a starting and ending points for RNA to be made

Transcription RNA polymerase uses one strand of DNA as a template to make the complementary strand of mRNA

DNA contains… Introns – nucleotide sequences that do NOT code for proteins   Exons – nucleotide sequences that do code for proteins

RNA polymerase copies both introns and exons, but before mRNA leaves the nucleus… Introns are cut out of the sequence Exons are spliced (glued) back together to form the final mRNA

mRNA travels to the ribosomes (outside of nucleus)

Translation

Translation mRNA  protein (occurs on ribosomes) mRNA attaches to a ribosome Starting at codon “AUG,” ribosome reads each codon Codon = 3 nucleotides

Translation For each codon, an amino acid is brought into the ribosome by tRNA Each tRNA molecule carries only one kind of amino acid Each tRNA has the anticodon, that is complementary to one mRNA codon

Translation A peptide bond forms between each amino acid as it is brought into the ribosome  polypeptide chain tRNA is released Polypeptide chain stops growing when the ribosome reaches a stop codon on the mRNA

Translation Polypeptide (protein) & mRNA are released from the ribosome

Review

Important Facts: 3 nucleotides = 1 codon = 1 amino acid 64 codon combinations, but only 20 different amino acids The properties of proteins are determined by sequence of amino acids