topic 4

• Describe the process of transcription

  1. DNA helicase breaks hydrogen bonds, separating the strands
  2. The antisense strand only acts as a template
  3. Free RNA nucleotides join by complementary base pairing
  4. Uracil with adenine (not thymine)
  5. RNA polymerase catalyses condensation reactions between adjacent nucleotides forming phosphodiester bonds
  6. In eukaryotes, pre-mRNA is spliced to remove introns (exons joined together)
• Describe the process of translation

  1. mRNA leaves the nucleus and binds to the ribosome
  2. mRNA codon binds to the complementary anticodon on tRNA
  3. tRNA brings a specific amino acid
  4. adjacent amino acids join via codensation reactions using ATP, forming peptide bonds
  5. tRNA molecule is released to pick up new amino acids from the cytoplasm
  6. The ribosome moved along the mRNA until a stop codon is reached, producing a polypeptide