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From Gene to Protein

From Gene to Protein. The connection between genes and proteins The synthesis and processing of RNA The synthesis of protein. The Connection between Genes and Proteins. The study of metabolic defects provided evidence that genes specify proteins One-gene-one-enzyme hypothesis.

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From Gene to Protein

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  1. From Gene to Protein • The connection between genes and proteins • The synthesis and processing of RNA • The synthesis of protein

  2. The Connection between Genes and Proteins • The study of metabolic defects provided evidence that genes specify proteins • One-gene-one-enzyme hypothesis

  3. Transcription and Translation: Two Main Processes • DNA synthesizes RNA: Transcription • RNA synthesizes Protein: Translation

  4. The Genetic Code • Triplet sequence of nucleotides • smallest units of uniform length to allow translation of all 20 amino acids • codon- triplet in mRNA

  5. Synthesis and Processing of RNA • Three types of RNA: mRNA, tRNA, and rRNA • eukaryotes have three polymerases • RNA polymerase II responsible for mRNA synthesis • Transcription subdivided into three stages: Initiation, elongation and termination • RNA must be processed before it can function

  6. Transcription • Initiation: RNA polymerase binds to promoter region,TATA box plays critical role during initiation • Elongation: RNA polymerase unwinds DNA and adds nucleotides, 10 bases long, grows 5' to 3' direction. • Termination: terminator sequence (AAUAAA) stops transcription • DNA reforms double helix, RNA “peals” off template DNA (gene)

  7. Transcription

  8. Transcription Animations • http://www.youtube.com/watch?v=-ygpqVr7_xs&feature=related • http://www.johnkyrk.com/DNAtranscription.html • http://vcell.ndsu.nodak.edu/animations/transcription/movie.htm

  9. Post Transcriptional Modification(RNA Processing) • Capping: modified GTP added to 5' end of mRNA • Poly (A) tail: 20-200 adenine nucleotides added to 3' end of mRNA • RNA splicing

  10. Functions of the 5' Cap • Protect mRNA from hydrolytic degradation • Identifies mRNA to the small ribosomal subunit

  11. Functions of the Poly (A) tail • Inhibit degradation if mRNA in the cytosol • Facilitate mRNA export from the nucleus • Separated from the stop codon by trailer sequence

  12. RNA Splicing • Introns: noncoding sequences that are removed • Exons: coding sequences that are spliced together • Small nuclear ribonucleoproteins (snRNPs): identify and help bring about the splicing process • Spliceosome: catalyzes splicing reactions

  13. RNA Splicing

  14. Role of Introns • May control gene activity • May allow a single gene to synthesize several different proteins

  15. Translation(The synthesis of proteins) • tRNA • Ribosomes • Aminoacyl-tRNA synthases

  16. tRNA • Interpreter between base sequence of mRNA and amino acid sequence of protein • 45 different types • About 80 nucleotides long • Anticodon base pairs with codon of mRNA

  17. Ribosomes • Coordinate the pairing of tRNA with mRNA • Two subunits • Constructed in the nucleus • Three binding sites: P site, A site and E site

  18. Aminoacyl-tRNA Synthase • 20 different types • Two steps: 1) activation of amino acid with AMP 2) attachment of the amino acid to tRNA

  19. Building a polypeptide(Translation) • Initiation: brings mRNA, tRNA, and the two ribosomal subunits together • Elongation: three-step cycle that adds amino acids one by one to the initial amino acid, requires cooperation of several • Termination: release of the polypeptide chain from the complex.

  20. Initiation • 5' cap attaches to small ribosome subunit • tRNA carrying methionine attaches to mRNA codon • Large ribosomal subunit attaches

  21. Elongation • Codon recognition: tRNA directed into the A site by an elongation factor • Peptide bond forms between adjacent amino acids • Translocation: amino acid in the A site is moved to the P site • mRNA moves through the ribosome 5'3' direction

  22. Termination • Termination sequence is encountered • Release factor binds to sequence • Release factor separates polypeptide and tRNA

  23. Videos and Websites • http://www.johnkyrk.com/DNAtranscription.html • http://www.youtube.com/watch?v=-ygpqVr7_xs&feature=related • http://vcell.ndsu.nodak.edu/animations/transcription/movie.htm • http://vcell.ndsu.nodak.edu/animations/transcription/index.htm • http://vcell.ndsu.nodak.edu/animations/mrnaprocessing/index.htm • http://vcell.ndsu.nodak.edu/animations/mrnasplicing/index.htm • http://vcell.ndsu.nodak.edu/animations/translation/index.htm

  24. Videos and Websites (2) • http://www.sumanasinc.com/webcontent/animations/content/lifecycleprotein.html • http://www.sumanasinc.com/webcontent/animations/content/lifecyclemrna.html • http://www.sumanasinc.com/webcontent/animations/content/proteinsecretion_mb.html • http://www.sumanasinc.com/webcontent/animations/content/polyribosomes.html • http://www.sumanasinc.com/webcontent/animations/content/translation.html • http://www.sumanasinc.com/webcontent/animations/content/mRNAsplicing.html

  25. Videos • http://vimeo.com/13497169 • http://www.dnatube.com/video/544/Signal-Recognition-Particle-SRP • http://www.wehi.edu.au/education/wehitv/dna_central_dogma_part_1_-_transcription/ • http://www.wehi.edu.au/education/wehitv/dna_central_dogma_part_2_-_translation/

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