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Biology 102

Biology 102. Gene Regulation and Expression Part 2. Lecture outline. Translation Review of what translation is Types of RNA and their functions Overview of translation Details of translation Information flow through cell. Review: Information Flow DNA=>mRNA=>Protein. mRNA. U. U. U.

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Biology 102

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  1. Biology 102 Gene Regulation and Expression Part 2

  2. Lecture outline • Translation • Review of what translation is • Types of RNA and their functions • Overview of translation • Details of translation • Information flow through cell

  3. Review: Information FlowDNA=>mRNA=>Protein

  4. mRNA U U U U U C A A A A A G G G G G G G 1 2 Three Types of RNA (review) mRNA catalytic site Largesubunit Ribosomecontains rRNA Smallsubunit tRNA docking sites Transfer RNA Met Attached amino acid anticodon

  5. Translation: An Overview

  6. Translation: Initiation • A tRNA with an attached methionine amino acid binds to a small ribosomal subunit, forming an initiation complex.

  7. Translation: Initiation (2) • The initiation complex binds to end of mRNA and travels down until it encounters an AUG codon in the mRNA. • The anticodon of the tRNA in the initiation complex forms base pairs with the AUG codon.

  8. Translation: Initiation (3) • The large ribosomal subunit binds to the small subunit, with the mRNA between the two subunits. • The methionine tRNA is in the first tRNA site on the large subunit.

  9. Translation: Elongation 1 • The second tRNA enters the second tRNA site • The tRNA that binds must be able to match its anticodon (CAA in this example) to base pair with the codon (GUU in this example) in the mRNA. • tRNAs with a CAA anticodon carry an attached valine amino acid, which was added to it by enzymes in the cytoplasm.

  10. Translation: Elongation 2 • The catalytic site on the large subunit catalyzes the formation of a peptide bond linking the amino acids • The two amino acids are now attached to the tRNA in the second binding position.

  11. Translation:Elongation 3 • The "empty" tRNA is released and the ribosome moves down the mRNA, one codon to the right. • The tRNA that is attached to the two amino acids is now in the first tRNA binding site and the second tRNA binding site is empty.

  12. Translation: Elongation 4 • Another tRNA enters the second tRNA binding site carrying its attached amino acid. • The tRNA has an anticodon that pairs with the codon. (Here, the CAU mRNA codon pairs with a GUA tRNA anticodon.) • The tRNA molecule carries the amino acid histidine (his).

  13. Translation: Elongation 5 • The catalytic site forms a new peptide bond, in this example, between the valine and the histidine. • A three-amino acid chain is now attached to the tRNA in the second tRNA binding site. • The empty tRNA in the first site is released and the ribosome moves one codon to the right.

  14. Translation:Termination • Binding of tRNAs, & formation of peptide bonds continues. • Ribosome reaches STOP codon (UAG). • Protein "release factors" signal the ribosome to release the protein. • The mRNA is also released and large & small subunits separate.

  15. U U U U U T T C A A A A A A A A A A T T G G G G G G C C C C C T G G G G G C C C C C Review: From DNA to amino acid chain gene etc. (a) complementaryDNA strand templateDNA strand etc. codons (b) mRNA etc. anticodons (c) tRNA etc. amino acids Methionine Glycine Valine etc. (d) protein

  16. (Cytoplasm) Overview ofInformation Flow within the cell DNA (Nucleus) Transcription 1 rRNA mRNA tRNA + Proteins tRNA Ribosomes mRNA tRNA-AA Translation 2 InactiveProtein Modification ActiveProtein 3 AminoAcids Degradation 4 Substrate Product

  17. The End

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