Adv Biology 1-2

Translation  Translation-the transfer of information from an RNA molecule into a polypeptide. Using the information in RNA to make a polypeptide. Polypeptide-a chain of amino acids, the precursor to a protein.

Translation cont’d  Translation is carried out by the ribosome. Ribosome-organelle that carries out translation. Made of two subunits (large and small). Subunits made of ribosomal RNA (rRNA) and proteins.

Translation cont’d  Translation begins when the two ribosomal subunits bind to the mRNA. Read the mRNA 5’ to 3’. Begins translation at the sequence AUG (start codon).

Translation cont’d  The ribosome reads the mRNA codons to find out which amino acids to use. Codon-a three base sequence of mRNA that codes for an amino acid. ○ AUG establishes the reading frame (which three bases make a codon). ○ Starting with AUG, the ribosome reads every three bases.

Translation cont’d  tRNA (transfer RNA) bring amino acids to the ribosome. Each amino acid has its own tRNA. Each tRNA has an anticodon, a three base sequence that recognizes a particular codon on an mRNA.

Translation cont’d  Base pairing between codon and anticodon ensures amino acids are put in the right order. The ribosome forms peptide bonds between amino acids, creating a chain. Once the peptide bond forms, the tRNA leaves to pick up another amino acid.

Translation cont’d  Translation ends when the ribosome reaches a stop codon. Stop codons (UAA, UAG, and UGA) signal for a protein to bind, not an amino acid. ○ A signal to terminate translation. The ribosome releases the polypeptide and splits back into its two subunits.

Translation cont’d  During translation, multiple ribosomes can read the same mRNA, one after the other. Allows multiple proteins to be made simultaneously. After translation, the mRNA is reused or recycled.