Translation

Types of RNA

  • 3 main types of RNA involved in translating

    • Messenger RNA (mRNA)

      • coded strip that will be converted to protein

      • taken from DNA

      • carries instructions from DNA, which is like a blueprint, for ribosome to make protein (for example what type, etc.)

    • Ribosomal RNA (rRNA)

      • makes up part of the structure of ribosome (regulates)

      • involved in decoding the mRNA

    • Transfer RNA (tRNA)

      • short RNA chain

      • Carries a amino acids

      • the 3 bottom coding have a specific top

      • carries amino acids and drops it into mRNA when building protein

Translation

  • 4 nucleotides → A T C G are converted into 20 amino acid

  • 3 nucleotides = one amino acids

  • Codon = 3 letter code of amino acids

  • AUG code → MET will always start protein

  • UAA, UAG, UGA → stop the protein from being built

tRNA

  • has a distinct shape with amino acid on one and an anticodon

  • anticodon the part that attaches to codon

  • aminoacylation →when tRNA binds to it’s specific amino acid

    • creates aminoacyl-tRNA

  • The Wobble hypothesis → the first two nucleotide positions of the codon will bind normally that last don’t matter

    Ribosomes

  • are made of large and small subunits each containing protein and rRNA

  • ribosomes decode mRNA into protein strand

  • they have 3 binding sites for tRNA

    • A (aminoacyl) site

    • P (petidyl) site

    • E (exit) site

Step 1: Initiating Translation

  • methionine-tRNA binds to P-site on the small ribosomal subunit

  • Ribosomes scans until it find the AUG start codon

  • aminoacyl-tRNA binds to AUG codon

  • the large ribosome attaches after

Step 2: Elongating Polypeptide Strand

  • tRNA enters the A site

  • ribosome moves along the mRNA

  • at P site the amino acid is removed from tRNA by peptidyl transferase and attached to tRNA at the A site

    • peptidyl transferase → transfer enzyme

    • Once the amino acid is removed the RNA shifts one codon position moving the empty tRNA to the E site, the tRNA with the growing chain to the P site and making space in the A site for the next aminoacyl-tRNA

Step 3: Termination

  • when the A site reaches the stop codon (UAA,UAG, UGA)

  • protein release factor binds instead of aminoacyl-tRNA

  • the polypeptide chain is released from P site as normal, but there is no amino acid in A site to bind to. So the polypeptide is let go

  • the ribosomal subunits detach

Mass-Producing Protein

  • one strand of mRNA can be translated by several ribosomes at once → which forms a polysome

    • When done the ribosomes go back to the beginning of mRNA & start again

  • allows the cell to make lots of protein