AP Bio Ch 17 part 1 translation


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AP Bio Ch 17 part 1 translation

  1. 1. From Genes to Proteins Transcription Ch. 17 Sections 17.1, 17.2, & 17.3
  2. 2. To aid in your notetaking… Key vocabulary terms are in orange, bold font and underlined
  3. 3. Overview of Concepts 1. The information in DNA is in the sequence of nucleotides 2. Transcription is the production of RNA 1. There are several types of RNA 2. mRNA is the transcribed code for a protein based on the DNA 3. mRNA is modified in eukaryotic cells before it is functional
  4. 4. “One gene-one polypeptide” hypothesis The work of Beadle & Tatum in the early 1900s w/ Neurospora supported the hypothesis that each gene codes for a particular enzyme “one gene-one enzyme revised to “one gene-one protein”, then “one geneone polypeptide”
  5. 5. RNA is the bridge between DNA & proteins There are some key differences between DNA & RNA DNA Sugar deoxyribose RNA Sugar - ribose Bases - A, T, C, G Bases - A, U, C, G Double stranded & very long Single stranded & shorter
  6. 6. To go from the DNA to proteins requires 2 major steps: Transcription & Translation Transcription - DNA to RNA Translation - RNA to protein We will focus on Transcription today
  7. 7. What is transcription? The DNA strand serves as a template for the synthesis of a complementary RNA strand
  8. 8. Why can’t we just go straight from DNA to proteins? Having a “middleman” in the form of RNA protects the all important DNA It is more efficient many copies of that gene can be made & used simultaneously
  9. 9. Quick Think What is transcription and why is it important in the synthesis of proteins?
  10. 10. Prokaryotes vs. Eukaryotes Prokaryotes - both transcription & translation occur in the cytosol, since there is no nucleus These processes can happen simultaneously Eukaryotes - transcription in nucleus, translation in cytosol
  11. 11. The synthesis of mRNA Messenger RNA is made in much the same way that DNA is replicated The DNA strand serves as a template for the linking of complementary base pairs
  12. 12. RNA polymerase This enzyme separates the DNA strands It also bonds the RNA nucleotides together It attaches at a special sequence of bases on the DNA called the promoter region
  13. 13. Types of RNA polymerase Only 1 type in prokaryotes Three types in eukaryotes RNA pol II is used in the synthesis of mRNA RNA polymerase
  14. 14. The stretch of DNA that gets transcribed is called the transcription unit This is the region of the DNA that contains the information for making the protein
  15. 15. Quick Think How does the process of transcription begin?
  16. 16. The 3 stages of Transcription 1. Initiation 2. Elongation 3. Termination start build break-off
  17. 17. Initiation  In prokaryotes - RNA pol recognizes the promoter region and binds directly to it  In eukaryotes - proteins called transcription factors attach to promoter 1st, then RNA pol II attaches  This whole thing is called a transcription initiation complex  An important promoter sequence in eukaryotes is called a TATA box It contains the bases TATAAAA
  18. 18. Elongation RNA pol untwists the DNA 10-20 bases at a time RNA strand is made in the 5’ to 3’ direction, with new bases added to the 3’ end As it gets longer, it peels away from the DNA chain & the DNA double helix reforms Several RNA pol can be working on the same gene at the same time, increasing the rate of transcription
  19. 19. Termination in Prokaryotes In prokaryotes RNA pol goes through a termination sequence, detaches, & releases the transcript. The transcript is available for immediate use by the cell
  20. 20. Quick Write Describe the process of transcription, including the 3 stages, in prokaryotes
  21. 21. Termination in Eukaryotes The pre-mRNA strand is cut off from the growing RNA chain RNA pol is still attached to the DNA and continues to transcribe it RNA pol continues much further down the DNA and eventually falls off
  22. 22. Quick Write How is termination of transcription different in prokaryotes versus eukaryotes? eukaryotes
  23. 23. Modification of the mRNA in eukaryotes Enzymes in eukaryotic cells modify the mRNA before it becomes functional This is why it is called premRNA In general, both ends of the pre-mRNA are altered Some of the middle parts may be cut out and the remains sliced together
  24. 24. 5’ cap The 5’ end is the end that was transcribed first A modified guanine nucleotide is added This is called the 5’ cap
  25. 25. 3’ poly-A tail 50-250 adenines are added at the 3’ end
  26. 26. Why??? The 5’ cap and the 3’ tail help to: Export mRNA from the nucleus Protect mRNA from hydrolytic enzymes Allow ribosomes to attach at the 5’ end
  27. 27. In eukaryotic genes and the transcribed mRNA, there are long non-coding regions between coding regions We call regions We call regions the non-coding introns the coding exons RNA splicing removes the introns & joins the exons to make a continuous coding sequence in the mRNA RNA splicing
  28. 28. How does it know what to cut out? There are regions at the ends of introns that are recognized by molecules called spliceosomes (an assembly of RNA and proteins) The spliceosomes cut out the introns and fuse the remaining exons
  29. 29. Quick Write What are some ways the RNA is modified before it is translated in eukaryotic cells?
  30. 30. Ribozymes Ribozymes are RNA molecules that function as enzymes in the splicing of RNA Their discovery eliminated the hypothesis that all enzymes were proteins
  31. 31. Why introns? Allows for alternative RNA splicing to occur Genes can code for more than one polypeptide depending on which segments are treated as exons during RNA splicing Introns increase the likelihood of crossing over (more places for it to occur if gene is longer) Exons from different genes may get combined Exon shuffling can lead to new proteins, increasing genetic variation
  32. 32. Quick Write How is the functional mRNA different from the DNA template that was used to produce it? Think of as many differences as you can. I can think of at least 7 differences.