Protein synthesis

• Where does protein synthesis occur?

  Ribosomes.
• What are the 2 stages of protein synthesis?

  Transcription and translation.
• What happens in transcription?

  A mRNA copy complementary to one gene on the DNA is created in the nucleus.
• Describe the process of transcription(5)

  1.DNA helicase breaks hydrogen bonds between the bases in the DNA which causes the DNA helix to unwind.

  2.One chain of the DNA acts as a template.

  3.Free RNA nucleotides in the nucleus align opposite exposed complementary DNA bases.

  4.The enzyme RNA polymerase bonds together the RNA nucleotides to create this RNA polymer chain.

  5.This is called pre-mRNA which still has to be modified into mRNA that is ready to leave the nucleus.
• What is the process that modifies pre-mRNA into mRNA?

  Splicing- a spliceosome splices out the introns and leaves behind just the exons(coding regions)
• What happens during translation?

  The process of creating the polypeptide chain by converting the genetic code carried by mRNA- and then tRNA brings the amino acid the mRNA is coding for.
• What happens at the start of translation?

  Once the modified mRNA has left the nucleus, it attaches to a ribosome in the cytoplasm. The ribosome attaches at the start codon.
• What happens once the mRNA is attached to the ribosome?

  The tRNA molecule with the complementary anticodon to the start codon align opposite the mRNA, held in place by the ribosome.

  The ribosome moves along the mRNA molecule to enable another complementary tRNA to attach to the next codon on the mRNA.
• What happens once the tRNA delivers the amino acids?

  The amino acids are joined by peptide bonds, this is catalysed by an enzyme and requires ATP.
• What happens toward the end of translation?

  This continues until the ribosome reaches the stop codon at the end of the mRNA molecule. The stop codon doesn't code for an amino acid and therefore the ribosome detaches and transcription ends.
• What kind of protein does translation create and what happens to it after?

  A primary structure of a protein.

  This polypeptide chain will now enter the golgi apparatus for further folding and modification to create the final protein.