8.4 - Polypeptide Synthesis - Transcription

• stages of polypeptide synthesis

  transcription

  translation
• what's transcription?

  process of making pre-mRNA using part of the DNA as a template
• polypeptide synthesis in eukaryotes

  transcription happens in the nucleus

  translation happens in the ribosomes in the cytoplasm
• polypeptide synthesis in prokaryotes

  don't have a nucleus so transcription and translation both happen in the cytoplasm
• What enzyme attaches to DNA at the start of a gene during transcription?

  RNA polymerase
• What is the role of DNA helicase in transcription?

  It breaks hydrogen bonds to unwind DNA
• What is used as a template to make pre-mRNA?

  Template strand of DNA
• How do free RNA nucleotides pair with the template strand?

  By forming complementary base pairs
• What does RNA polymerase do as it moves along the DNA strand?

  Joins nucleotides together to form pre-mRNA
• What happens to the DNA strands after RNA polymerase passes?

  Hydrogen bonds between DNA strands reform
• What signals RNA polymerase to stop making pre-mRNA?

  A particular base sequence (stop signal)
• What is the process of splicing in pre-mRNA?

  Introns are removed, leaving exons
• What is formed after splicing pre-mRNA?

  mRNA
• How does mRNA exit the nucleus?

  Through nuclear pores
• Where does mRNA attach after leaving the nucleus?

  To ribosomes in the cytoplasm
• What are the main steps of transcription?

  1. RNA polymerase attaches to DNA
  2. DNA unwinds as hydrogen bonds break
  3. Template strand is used to synthesize pre-mRNA
  4. RNA polymerase joins nucleotides to form pre-mRNA
  5. RNA polymerase stops at the stop signal
  6. Pre-mRNA is spliced to remove introns
  7. mRNA exits the nucleus through nuclear pores
  8. mRNA attaches to ribosomes for translation
• does splicing happen in eukaryotes and prokaryotes?

  only happens in eukaryotes

  doesn't happen in prokaryotes because they don't have introns
• Why does splicing need to happen?

  introns don't Code for anything so would prevent the synthesis of a polypeptide if it isn't removed

  pre-mRNA molecules are too large to leave the nucleus where as RNA molecules are smaller so can leave