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Gene Expression: From DNA to Protein

Gene Expression: From DNA to Protein. Background. Watson & Crick Beedle & Tatum. How Genes are Expressed. Processes: Transcription (DNA to mRNA) Translation (mRNA to protein) Importance of location Eukaryotes Prokaryotes. RNA. Review Types of RNA in Gene Expression

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Gene Expression: From DNA to Protein

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  1. Gene Expression: From DNA to Protein

  2. Background • Watson & Crick • Beedle& Tatum

  3. How Genes are Expressed • Processes: • Transcription (DNA to mRNA) • Translation (mRNA to protein) • Importance of location • Eukaryotes • Prokaryotes

  4. RNA • Review • Types of RNA in Gene Expression • mRNA (messenger)-provides code for protein • tRNA (transfer)-carries amino acids • rRNA (ribosomal)-directs translation

  5. Transcription • Requires DNA-dependent RNA Polymerase • Core enzyme + sigma factor = holoenzyme • Three forms in Eukaryotic Nuclei • RNA Pol I –Pre-rRNA • RNA Pol II**--Pre-mRNA • RNA pol III –Pre-tRNA

  6. Stage One: Intiation • RNA recognizes region to be transcribed • Promotor regions • TATA box • CAAT box

  7. Stage Two: Elongation • Complementary mRNA produced from DNA

  8. Stage Three: Termination • Often zones with high GC levels • Loop and release of mRNA • Protection • 5’ capped with 7-methyl G • 3’ tail polyadenylation

  9. Translation • Prokaryotic cells translate immediately into protein • Eukaryotic cells process mRNA before translation occurs • Cutting out Introns • Protecting transcript

  10. Processing mRNA • Splicing occurs by sequence • snRNA and snRNP (spliceosomes), and/or ribozymes (self-splicing enzymes) • Many different proteins can result from one transcript

  11. Requirements for Translation • mRNA • Transcript • tRNA • Carrier for amino acids • Ribosomes • Two sub-units of protein with three pieces of RNA

  12. Nucleotide Sequence to Protein • Codons- 3 nucleotide codes for amino acids • 20 amino acides • 64 codons • 3 stop codons (UGA, UAA, UAG) • 1 Start codon (AUG-methionine) • Each codon brings in a tRNA anti-codon that contributes one amino acid to the protein

  13. Stage One: Initiation • Small sub-unit of ribosome binds to mRNA • Methionine “start” • Large sub-unit of ribosome enters • Initiation factors involved

  14. Stage Two: Elongation • Connection • Next tRNA enters • 1sttRNA “hands” amino acid to 2ndtRNA, then leaves • Ribosome slides to free the next space • Continuationfor length of protein • Elongation factors involved

  15. Stage Three: Termination • Stop Codon is reached • RF’s bind to stop codon • Protein is released • Ribosomal units disassociate

  16. For our next session: • Exploring factors influencing gene expression • Expression and repression of genes

  17. References • Brooker, R. J. (2011). Concepts of Genetics + Connect Plus Access Card. McGraw-Hill Science Engineering, New York, NY. • Brooker, R. J., (2012). Genetics: analysis and principles. 4th Ed. McGraw-Hill Higher Education, New York, NY. • King, M. D. (2013). The Medical Biochemistry Page. Retrieved from: http://themedicalbiochemistrypage.org/home.html. • McClean, P. E. (2013). Transcription. Retrieved from: http://www.ndsu.edu/pubweb/~mcclean/plsc731/transcript/transcript1.htm • Unknown (2013). Three types of RNA polymerase in eukaryotic nuclei. Retrieved from: http://mcb.berkeley.edu/courses/mcb110/ZHOU/lec.5-7.euk_trxn_apparatus.pdf

  18. Image Sources • Cap & Tail http://classconnection.s3.amazonaws.com/681/flashcards/894681/jpg/coding1330783434942.jpg • RNA Elongation http://limbiclab.files.wordpress.com/2012/12/limbic_lab_dna_transcription_diagram1.png • RNA Initiation http://9e.devbio.com/images/ch05/0503fig1.gif • Processing http://www.genomebc.ca/glossary/Alternative%20Splicing%20(colourful)_Image.gif • Translation Initiation http://kvhs.nbed.nb.ca/gallant/biology/translation_initiation.jpg • Translation Elongation http://kvhs.nbed.nb.ca/gallant/biology/translation_elongation.jpg • Translation Termination http://utminers.utep.edu/rwebb/assets/images/17.17_Termination_of_transla.jpg

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