Biology · MU Sofia

5. Transcription.

Explains transcription as RNA synthesis from a DNA template, covering its general characteristics, the role and structure of RNA polymerase, and the energy source for the reaction. It then walks through initiation, elongation and termination, the transcription unit, and differences between prokaryotic and eukaryotic systems. Includes a clinical note on the death cap mushroom toxin, plus mnemonics for the stages, subunits and eukaryotic polymerases.

Inside: 11 sections · 2 labelled pictures · 25 flashcards · 2 min

Topic 6 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 11 sections, about 275 words (2 min of reading), with 25 flashcards.

In this note

  1. Transcription:
  2. Definition
  3. General Characteristics
  4. Enzymes Involved
  5. Energy in Transcription
  6. Stages of Transcription
  7. Transcription Unit
  8. Prokaryotic Transcription
  9. Eukaryotic Transcription
  10. Clinical Note: Death Cap Mushroom
  11. Mnemonics

Definition

Transcription is the process by which RNA is synthesized using a DNA segment as a template.

General Characteristics

  • DNA stores genetic information.
  • Genes are expressed via transcription into RNA.
  • RNA is synthesized from the 5' to 3' direction.
  • RNA and DNA strands are antiparallel and complementary.
  • Specific promoter and terminator sequences define start and end.

Enzymes Involved

DNA-dependent RNA Polymerase:

  • Separates DNA strands temporarily.
  • Uses one DNA strand as a template.
  • Catalyzes phosphodiester bond formation.
  • Involved in gene regulation.

Structure: Complex quaternary protein.

Energy in Transcription

  • Ribonucleotides (ATP, UTP, GTP, CTP) provide energy.
  • Energy released from phosphate bond cleavage.
  • Pyrophosphate hydrolyzed by pyrophosphatase, pushing reaction forward.

Stages of Transcription

1. Initiation

  • Transcription factors bind TATA box (promoter).
  • RNA Polymerase forms the transcription initiation complex.
  • DNA unwinds, and phosphodiester bonds begin forming.

2. Elongation

  • RNA Polymerase adds complementary nucleotides to the 3' end of RNA.
  • DNA helix reforms after polymerase passes.
  • Topoisomerases relieve supercoiling.

3. Termination

  • RNA Polymerase halts at terminator sequence.
  • Transcript is released.

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