Information Transfer part 1

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Lecture slides for Bio I, Hon. on 4/17/07.

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Information Transfer part 1

  1. 1. Information Transfer and Protein Synthesis
  2. 2. “Central Dogma” DNA mRNA Protein (polypeptide)
  3. 3. Molecular Code • DNA stores/transmits a “code” • 4 nitrogen bases A, T, C, G • 20 essential amino acids A colored scanning electron micrograph of a group of human chromosomes (x6,875)
  4. 4. Transcription Transcription is the process by which one strand of the DNA is copied to form a complimentary strand of messenger RNA (mRNA)
  5. 5. Transcription
  6. 6. Transcription initiation elongation termination
  7. 7. initiation • RNA polymerase binds to the DNA at the promoter region • DNA unwinds exposing the coding strand
  8. 8. elongation • DNA acts as a template (pattern) for the mRNA • RNA polymerase moves along DNA elongating (making longer) the mRNA strand
  9. 9. termination • RNA polymerase reaches the terminator region on the DNA • RNA is release RNA polymerase falls off
  10. 10. A transmission electron micrograph of an unidentified operon of the bacterium Escherichia coli, x72,600. Ribosomes attach to mRNA, and protein synthesis begins even before transcription is complete.
  11. 11. RNA Processing • the primary mRNA transcript may be 200,000 nucleotides in length • mRNA in the cytoplasm is only a few 1000 nucleotides in length • mRNA is modified (processed) before leaving the nucleus
  12. 12. Enzymes attach a cap of chemically modified guanine nucleotides (methyl- guanine, or mG) to the starting end of the mRNA molecule
  13. 13. Other enzymes then replace part of the opposite end with a tail of 100–200 adenine nucleotides called a poly- A tail
  14. 14. The final step in mRNA processing involves removal of some internal segments of the RNA that do not code for protein called introns
  15. 15. The parts of the transcript that remain (and code for protein) are called exons. They are joined together in a process called splicing.

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