Transcription and Translation

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Transcription and Translation

  1. 1. Transcription and Translation www.ibscrewed.org
  2. 2. DNA vs. RNA DNA RNA Deoxyribose sugar (pentose) Ribose sugar (pentose) Bases: A, T, G, C Bases: A, U, G, C Double-strand helix Single-strand helix Very long Relatively short
  3. 3. What is transcription? Since our DNA molecules are too large to leave the nucleus, a smaller mRNA molecule is formed. Takes place in the nucleus – 5i to 3i direction
  4. 4. HL Stuff to know Starting point is the “promoter region” Nucleotides are attached by RNA polymerase Covalent bonds between nucleotides Moves along the antisense strand Stops when it reaches the “terminator sequence” Introns are removed through splicing and broken down in the nucleus – makes mature mRNA
  5. 5. DNA helicase – RNA polymerase
  6. 6. Codons Triplets of bases on the mRNA strand Some are start codons and stop codons
  7. 7. Translation Takes place in the cytoplasm – 5i to 3i Ribosomes are the enzymes – small subunit and large subunit
  8. 8. Activation of tRNA The corresponding amino acid binds to the tRNA at the 3i end Uses tRNA-activating enzyme The code is degenerate – one amino acid may bind to different types of tRNA
  9. 9. Code: A = Blue U = Red G = Yellow C = Green
  10. 10. Initiation First tRNA molecules binds to the start codon AUG
  11. 11. Elongation More tRNA bind, polypeptide bonds form between amino acids
  12. 12. Translocation The tRNA has detached from its amino acid and is released from the E (exit) site
  13. 13. Termination Ribosome reaches stop codon (no matching tRNA), mRNA is released and ribosome separates Polypeptide folds into secondary, tertiary structure
  14. 14. Gene = Polypeptide??? Most of the time, yes BUT! – some genes do not code for mRNA that produces polypeptides Some just control the expression of other genes Does it matter where the ribosome is?? YES! Free in the cytoplasm = protein used in the cell Attached to ER = secreted outside the cell
  15. 15. Peptide bond

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