8.5 - Polypeptide Synthesis - Translation

• Where does translation happen?

  in the ribosomes in the cytoplasm (both in eukaryotes and prokaryotes)
• What happens during translation?

  amino acids are joined together to form a polypeptide chain
• What is the first step in the stages of translation?

  Ribosome attaches to starting codon
• What does tRNA do during translation?

  It pairs with codon on mRNA
• What provides energy for the bond between tRNA and amino acid?

  ATP
• How does the ribosome move during translation?

  It moves along mRNA bringing tRNA together
• What happens to the two amino acids on tRNA during translation?

  They are joined by a peptide bond
• What role does the enzyme play in translation?

  It helps form peptide bonds
• What happens to tRNA after it releases its amino acid?

  It moves away to pick up more amino acids
• When does the process of translation stop?

  When there's a stop codon on mRNA
• What happens to the ribosome, mRNA, and last tRNA after translation?

  They all separate and complete the polypeptide chain
• What are the main stages of translation?

  1. Ribosome attaches to starting codon
  2. tRNA pairs with mRNA codon
  3. Peptide bond forms between amino acids
  4. tRNA moves away, picks up more amino acids
  5. Process repeats until stop codon is reached
  6. Ribosome, mRNA, and tRNA separate, polypeptide chain is complete
• how do genes control the cell's activities?

  gene determines sequence of codons on mRNA which determines the order tRNA lines up which determines the sequence of amino acids so determines what proteins are made, many of which are enzymes
• who discovered what codes for each amino acid?

  Nirenberg and Khorana
• what was Nirenberg's experiment?

  cell extracts with components to make polypeptides lwere obtained and treated with DNase

  synthetic mRNA Mas oadded to extract & all 20 amino acids attached to their tRNA

  One amino acid was radioactively labelled with 14-C & the other 19 had normal, non-radioactive 12-C

  extracts were incubated & polypeptide produced was later extracted

  radioactivity level of polypeptide produced in each case was measured
• how many codons did Nirenberg decode?

  47 out of 64 codons
• Khorana's experiment

  decoded the other 17 codons by forming very long MRNA Molecules that had repeating sequences of nucleotide bases b seing what amino acids they made