Genes and How they Work
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Transcript of Genes and How they Work
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Genes and How they Work
Chapter 15
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The Nature of Genes
• Garrod
• Beadle and Tatum
• Francis Crick
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Beadle and Tatum Experiment• Used Neurospora crassa
• One gene/one polypeptide hypothesis
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Central Dogma of Molecular Biology
• DNA- RNA- Protein
• Transcription to translation
• Rule breakers? – Retrovirusese– Reverse Transcriptase
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The Genetic Code
• Crick and Brenner– Codons– Spaced or Unspaced?– Frameshift Deletions
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Nirenberg Deciphered the Code
• http://img.sparknotes.com/figures/1/132e5720f3b37836571a1aeb9d163ac3/genetic_code.gif
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Genetic Code Almost Universal
• So where is it not the same?
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Transcription
• Template Strand
• Coding Strand
• mRNA– Initiation– Elongation– Termination
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Translation
• tRNA
• Takes place on the ribosome
• http://library.thinkquest.org/C004535/media/translation.gif
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Types of RNA
• mRNA- make RNA from DNA template• rRNA- found in ribosomes• tRNA-adapter molecule between mRNA and
AA’s• snRNA’s- involved in the nuclear processing
of eukaryotic pre-mRNA• SRP RNA-mediate protein synthesis in
eukaryote• Micro-RNA- newly discovered
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Eukaryotic vs. Prokaryotic Gene Expression
Characteristic Prokaryotes EukaryotesIntrons No introns Most genes have
introns
Number of genes in mRNA
Several for each mRNA Only one gene per mRNA
Site of Transcription and Translation
No membrane bound nucleus- t and t are coupled
Transcription in nucleus, outside nucleus for translation
Initiation of Translation Begins at AUG preceded by special sequence that binds the ribosome
Gegins at AUG preceded by the 5’ methylated GTP cap
Modification of mRNA after transcription
none Introns are removed, a 5; cap is added; poly A tail is added
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Videos
• Eukaryotes vs prokaryotes
• Translation
• spliceosome
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Words to know
• Promoter
• Terminator
• Operon
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Spliceosome
• http://fig.cox.miami.edu/~cmallery/150/gene/sf13x8bc.jpg
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Types of Mutations
• Point Mutations– Bases substitution
• Missense vs nonsense
– Frameshift
• Chromosomal Mutations– Deletions– Duplications– Inversions– Translocations
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Point Mutations
• http://kvhs.nbed.nb.ca/gallant/biology/point_mutations.jpg
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Chromosomal Mutations
• Page 300 in text