TRANSCRIPTION

• What is the first stage of protein synthesis called?

  Transcription
• Describe what happens during transcription

  An mRNA copy of a gene is made from DNA.
• Where does transcription take place in eukaryotic cells?

  In the nucleus
• Where does transcription take place in prokaryotic cells

  In the cytoplasm
• Why does transcription take place in the cytoplasm in prokaryotic cells?


  Prokaryotes do not hace a nucleus
• When does transcription start?

  When an enzyme called RNA polymerase attaches to the DNA double-helix at the beginning of the genee
• What is the first stage of transcription?

  Transcription starts when the enzyme RNA polymerase attaches to the DNA double-helix at the beginning of a gene
• what is the second stage of transcription?

  (Eukaryotes) The hydrogen bonds between the two DNA strands in the gene are broken by a DNA helicase attached to the RNA polymerase

  • this separates the strands and the DNA molecule uncoils, exposing some of the bases
• what is the third stage of transcription?

  One of the strands used as a template to make an mRNA copy
• what is the fourth stage of transcription?

  RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand.

  • the free bases are ATTRACTED to the exposed bases
  • specific complementary base pairing = the mRNA strand ends up being a complementary copy of the DNA template strand ( but T replaced by U)
• What is stage 5 of transcription?

  Once the RNA nucleotides have paired up with their specific bases on the DNA strand they are joined together by RNA polymerase, forming an mRNA molecule
• What is stage 6 of transcription?

  RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand
• What is stage 7of transcription?

  The hydrogen bonds between the uncoiled strands of DNA re-form once the RNA polymerase has passed by and the strands coil back into a double-helix
• What is stage 8 of transcription?

  When RNA polymerase reaches a particular sequence of DNA called a stop signal, it stops making mRNA and detaches from the DNA
• What is stage 9 of transcription?

  (eukaryotes)mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm , where the next stage of protein synthesis takes place