Transcription

• Where does it occur ?

  in the nucleus
• Transcription steps ( 6 marks)?

  1.DNA double helix unzipped by helicase ( hydrogen bonds broken)- this is the template strand

  2. RNA nucleotides align next to their complementary bases on the template strand forming H bonds and Uracil replaces thymine in RNA

  3.RNA polypeptide joins adjacent nucleotides ( condensation reactio)

  4. Forming phosphodiester bonds

  5.When RNA polymerase reaches stop codon mRNA/ pre-mRNA detaches from DNA

  6. mRnA leaves the nucleus via nuclear pores
• Eukaryotic genes contain exons , what are they ?


  coding regions
• What are introns?

  non- coding regions
• What is splicing?

  Splicing is the process of removing introns and joining exons together in different combos for different proteins to be formed.
• Prokaryotic DNA doesn’t contain introns, so it is shorter than eukaryotic DNA and so mRNA produces directly from DNA. no splicing needed
• Why Does prokaryotic DNA not need splicing?

  Lack of introns