Protein Synthesis

• Give the two types of molecule from which a ribosome is made.

  Ribosomal proteins; ribosomal RNA.
• Describe the role of a ribosome in the production of a polypeptide. Do not include transcription in your answer.

  1. mRNA binds to ribosome;
  2. Two binding sites;
  3. Allow tRNA with anticodons to bind;
  4. Catalyses the formation of peptide bond between amino acids;
  5. Moves along mRNA to the next codon (translocation).
• In a eukaryotic cell, the base sequence of the mRNA might be different from the sequence of the pre-mRNA. Explain why.

  The pre-mRNA strand is spliced and introns are removed.
• Describe the process of protein transcription.

  • DNA helicase binds to a complementary start codon on the DNA and breaks the hydrogen bonds, causing the DNA to unwind and expose its bases, to which free-floating RNA nucleotides bind
  • RNA polymerase moves along the DNA strand, causing hydrogen bonds to form between the RNA bases to make a strand of RNA nucleotides
  • the double helix reforms behind polymerase, which detaches once it reaches a stop codon
  • pre-mRNA is too large to fit through the nuclear pores and leave the nucleus so it gets spliced to remove its non-coding introns
• Messenger RNA (mRNA) is used during translation to form polypeptides. Describe how mRNA is produced in the nucleus of a cell (AKA describe the process of transcription).

  • helicase;
  • breaks hydrogen bonds;
  • only one DNA strand acts as a template;
  • RNA nucleotides are attracted to the exposed bases;
  • attraction according to the base pairing rule;
  • RNA polymerase joins RNA nucleotides together;
  • pre-mRNA is spliced to remove introns;
• Describe the structure of proteins.

  • polymer of amino acids;
  • joined by peptide bonds;
  • formed by condensation;
  • the primary structure is the order of amino acids;
  • the secondary structure is the folding of the polypeptide chain due to hydrogen bonding;
  • the tertiary structure is 3-D folding due to hydrogen bonding and ionic/disulfide bonds;
  • the quaternary structure is two or more polypeptide chains;