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Transcription. Central Dogma of Biology. Information flows from DNA  RNA  Proteins Think of it as exchanging money in a different country: proteins cannot be built directly from DNA Three main processes involved: Replication (copies DNA) Transcription : DNA  RNA

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  2. Central Dogma of Biology • Information flows from DNA  RNA  Proteins • Think of it as exchanging money in a different country: proteins cannot be built directly from DNA • Three main processes involved: • Replication (copies DNA) • Transcription: DNA  RNA • Translation: RNA  Protein

  3. RNA vs. DNA • 3 main differences: • Sugar is called ribose (DNA has deoxyribose) • Uracil (U) instead of thymine • pairs with adenine (A) • Single-stranded

  4. RNA Molecules • 3 major types • Messenger RNA (mRNA): codes for proteins • Ribosomal RNA (rRNA): part of the ribosome • Transfer RNA (tRNA): helps read the mRNA code to build proteins during the process of translation

  5. What is Transcription? • Transcription is a process that uses a portion of DNA to make a complementary RNA strand • Similar to replication • Just one gene at a time is transcribed, not the whole DNA molecule

  6. Transcription Process • 3 basic steps, just as in replication: • Part of DNA double helix unwinds (initiation) • Complementary RNA bases are assembled (elongation) • Completed RNA strand detaches from DNA (termination)

  7. Initiation • RNA polymerase finds the beginning of a gene • A transcription complex made of RNA polymerase and other enzymes begins to unwind part of the DNA strand

  8. Elongation • RNA polymerase uses the DNA strand as a pattern to build a complementary RNA strand • C pairs with G • A pairs with U • RNA strand hangs off the DNA strand, and DNA helix zips back together

  9. Termination • After the whole gene has been transcribed, the RNA strand detaches completely from the DNA. • The transcription complex made of RNA polymerase and other proteins falls apart.

  10. Replication vs. Transcription

  11. Replication vs. Transcription

  12. Replication vs. Transcription

  13. Replication vs. Transcription

  14. Replication vs. Transcription

  15. Replication vs. Transcription

  16. Transcription Practice • Write a DNA sequence 6 bases long • Write the complementary strand, showing H bonds between bases • Count how many of each base are in your DNA molecule. How does this relate to Chargaff’s rule? • List 3 differences between DNA and RNA • Circle one DNA strand. Simulate transcription by writing its complementary RNA sequence. • Does the RNA strand more closely resemble the DNA strand from which it was transcribed or the complementary strand that wasn’t used? Why? • What is the main enzyme involved in transcription? What is its function? • List 3 types of RNA and briefly describe each one.

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