Transcription

• What is the genome?

  The complete set of genes in a cell (including in mitochondria and chloroplasts)
• What is the proteome?

  The full range of proteins produced by the genome.
• What are the two stages of protein synthesis called?

  Transcription and translation
• Describe the structure of mRNA.

  A long, single strand. Its base sequence is complementary to the DNA it was formed from.
• What is the role of mRNA?

  mRNA carries genetic information from DNA to the ribosomes for protein synthesis
• Suggest the advantages of using mRNA rather than DNA for translation.

  • Shorter and contains uracil which means that it breaks down quickly so no excess polypeptide forms
  • Single-stranded and linear which means that the ribosomes moves along the strand & tRNA binds to the exposed bases
  • Contains no introns
• Describe the structure of tRNA.

  A single strand that is folded into a clover leaf shape. On one end there is an anti-codon, and on the opposite end there is an amino acid binding site.
• What is the role of tRNA?

  tRNA transports amino acids to the ribosomes to build a polypeptide chain.
• What is produced by transcription?

  mRNA
• What is transcription in simple terms?

  The production of mRNA from DNA
• Where does transcription take place?

  In the nucleus
• What has to happen to the mRNA before it can leave the nucleus?

  Pre-mRNA must be spliced to remove introns which leaves only the coding regions. Then it moves out of the nucleus through a nuclear pore and attaches to a ribosome.
• How is transcription different in eukaryotic cells vs prokaryotic cells?

  In prokaryotes, transcription results directly in the production of mRNA from DNA whereas in eukaryotes transcription results in the production of pre-mRNA; this is then spliced to form mRNA.
• Why do hydrogen bonds need to broken in transcription?

  To unwind the double helix and separate the DNA strands
• What is the role of RNA polymerase in transcription?

  RNA polymerase forms phosphodiester bonds between RNA nucleotides to form an mRNA molecule
• What happens when RNA polymerase reaches a stop signal?

  It stops making mRNA and detaches from the DNA
• What is splicing?

  Splicing is the process of removing introns from a pre-mRNA molecule.
• Why does prokaryotic mRNA not undergo splicing?

  It does not contain introns.
• What are the steps involved in transcription?

  1. Hydrogen bonds are broken to unwind the double helix and separate the DNA strands
  2. Free RNA nucleotides attract to their complementary bases on one DNA strand.
  3. RNA polymerase forms phosphodiester bonds between RNA nucleotides to make mRNA
  4. When RNA polymerase reaches a stop signal, it stops making mRNA and detaches from the DNA.
• Which enzymes are involved in transcription?

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

  Catalyses the breaking of hydrogen bonds between the two strands of DNA
• What is the role of RNA polymerase during transcription?

  Joins adjacent RNA nucleotides together, forming a phosphodiester bond