4. Transcriptase and Translation

• Stages of Transcription: 1. RNA polyermase attaches to DNA

  • RNA polyermase attaches to DNA at start of gene. Exposed bases are used as template to produce mRNA copy.
  • In eukaryote: hydrogen bonds between DNA strand broken with DNA helicase
  • in prokaryote: DNA strand are separated by only RNA polyermase
• Stages of Transcription: 2. Complementary mRNA is formed

  • RNA polyermase lines up free RNA complementary nucleotides alongside exposed bases on template strand
  • Complementary copy of template DNA strand is produced
  • RNA polyermase joins nucleotides together to form mRNA
• Stages of Transcription: 3. RNA polyermase moves down DNA strand

  • RNA polyermase moves along assembling mRNA
  • Hydrogen bonds between uncoiled strand of DNA reform once RNA polyermase has passed
  • strand coil back into double-helix
• Stages of Transcription: 4. RNA polyermase reaches stop signal

  • RNA polyermase reaches stop signal and detaches from DNA
  • In eukaryotes, mRNA moves out of nucleus through nuclear pore
• Editing mRNA- eukaryotes:

  • Introns and exons are copied into pre-mRNA during transcription
  • splicing: Introns removed, exons are joined, forming mRNA
• Editing mRNA- Prokaryote

  • mRNA is produced directly from DNA- prokaryotes don’t have introns
• Translation stage:1

  • mRNA attaches to ribosome
  • ATP provides energy to bond amino acids to tRNA
  • tRNA molecule carries amino acids to mRNA
• Translation stage:2

  • tRNA anticodon attaches to first codon on mRNA via complementary base pairing
  • second tRNA/ amino acid attaches to next codon
• Translation stage:3

  • 2 amino acids are joined by a peptide bond
  • the first tRNA molecule moves away
• Translation stage: 4

  • Process of 2 amino acids joined together continues, producing chain of linked amino acids
  • Ribosome reaches stop signal on mRNA and polypeptide chain moves away