DNA and protein synthesis

• What are the two stages of protein synthesis?


  transcription and translation
• where does transcription occur?

  in the nucleus
• what does transcription involve?

  DNA and mRNA
• What does translation involve?

  mRNA , tRNA , and RIBOSOMES
• what happens during transcription?


  A section of a DNA strand is transcribed into mRNA which is then TRANSLATED into a polypeptide chain formed of amino acids
• what does mRNA stand for?

  messenger RNA
• what does tRNA stand for?


  transfer RNA
• What is messenger RNA?


  This is a long, single strand created during transcription in which the base sequence is complementary to DNA. Each set of three bases (called the codon) match a triplet on the DNA as well as the tRNA
• How many nucleotides is tRNA made out of?

  around 80
• is tRNA a small or big molecule?

  a small molecule made up of around 80 nucleotides
• what is tRNA?

  • small molecule made from 80 nucleotides
  • single strand folded up into a clover leaf shape in which one end extends from the others - this is where an amino acid attaches
  • at the opposite end is an anti-codon
  • the anti-codon is specific to the amino acid that the tRNA attaches to.
• briefly what happens during transcription?

  a molecule of mRNA is made in the nucleus
• How is mRNA produced from a template strand ofDNA that is exposed?


  Free nucleotides form complementary base pairs

  Phosphodiester bonds form by the action of RNA polymerase
• in eukaroytes, how is mRNA produced from transcription?

  • hydrogen bonds between DNA bases break
  • only one DNA strand acts as a template
  • free RNA nucleotides align by complementary base pairing
  • in RNA uracil base pairs with adenine on DNA
  • RNA polymerase joins adjacent RNA nucleotides by phosphodiester bonds between adjacent nucleotides
  • pre-mRNA is spliced to form mRNA
• How is mRNA produced in the nucleus of a cell (6 marks )?

  • helicase
  • breaks hydrogen bonds
  • only one DNA strand acts as a template
  • RNA nucleotides attached to exposed bases
  • attraction according to base pairing rule
  • RNA polymerase joins (RNA ) nucleotides together
  • pre-mRNA spliced to remove introns