6 Translation and transcriptional regulation ppt

6 Translation and transcriptional regulation ppt -...

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Translation and  Transcriptional Regulation Covering:  Chapter 7  &   Chapter 8 Alberts et al. 2014 Part II
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By end of 1950’s the central dogma was well established. But the means to get 4 nucleotides in RNA to make  20 unique amino acids  remained unclear .  There  simple 1:1 correspondence of  1 nucleotide : 1 amino acid.  mRNA Synthesized:  5’ 3” direction mRNA Read: 5’  3’ direction Polypeptide Chain Made: Amino   Carboxyl Terminus
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Peptide Bonds Link Together Linear Chains of  Amino Acids Forming Polypeptides Note: Structural  Polarity 
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Figure 4-1 Essential Cell Biology (© Garland Science 2010)
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Twenty Different Amino Acids  Commonly Found in Proteins 
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The Genetic Code  1961 – Discovery RNA nucleotide sequences read in groups of 3 with 4X4X4 =64 possible combinations.  Genetic code was found to be REDUNDANT - some triplets code for >1 amino acid. CODONS  – each group of three consecutive nucleotides in RNA The SAME Genetic Code is used in ~ all present day organisms. 
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mRNA  can be translated into any of 3 unique reading frames,  always read 5’   3’ direction, but only 1  encodes actual protein:
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The Genetic Code 1 ) Each amino acid is specified by three adjacent bases  known as a  codon . 2) The genetic code is almost universal (exceptions with mitochondria, fungi & protozoa).  3) A codon is not directly recognized by amino acids.  4) The code is degenerate  (64 codons and 20 amino acids).  5) The code is contiguous and non-overlapping (there are no pauses or gaps). 6)  The genetic code is redundant : > 1 codon may specify a particular amino acid. But it is not ambiguous : no codon specifies > 1 amino acid.
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Each Amino Acid is Specified by One or More  Codons in the Genetic Code Each amino acid   specified by three  adjacent bases  (codon) The code is ~ universal Each amino acid is represented by one or more codons (redundant)
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(a) Tobacco plant expressing a firefly gene (b) Pig expressing a jellyfish gene Due to the universal genetic code, genes can be transcribed and translated after being transplanted from one species to another making “genetic engineering” possible.
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3. tRNAs have two        “active sites” which  recognize and bind a  codon on one side and          an amino acid on  other.  Codons are NOT directly recognized by amino acids: 1.  Transfer RNAs (tRNAs) adapter molecules carry           amino acids to codons in the mRNA 2. tRNAs are  ~80 nucleotides       long with a classic clover        leaf like structure.
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tRNAs Act as Molecular Adaptors Between mRNA  Template and the Incorporating Amino Acid The Adaptor Hypothesis of Francis Crick “Charged” tRNA for Phe
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“Charged” 
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