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28 Cards in this Set
- Front
- Back
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Transcription |
- RNA synthesis under the direction of DNA - RNA produced complementary sequence to the template DNA. |
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3 Types of RNA Produced |
- mRNA: carries the message for protein synthesis - tRNA: carries amino acids during protein synthesis - rRNA: components of ribosomes |
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Template Strand |
- directs RNA synthesis - is read in 3' to 5' direction |
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Promoter |
- located at the start of the gene - is the recognition/binding site for RNA polymerase - functions to orient polymerase a specific distance from first DNA nucleotide that will serve as a template - important in regulating when a gene will be transcribed or expressed |
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Leader sequence |
Transcribed into RNA but is translated into amino acids - in bacteria, includes Shune-Dalgamo sequence, important for initiation of translation |
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Coding Region |
- beings with the DNA sequence 3'-TAC-5' - produces codon AUG - codes for N-formulmethione, a modified amino acid used to initiate protein synthesis in bacteria - ends with a stop codon (UGA, UAG, UAA), immediately followed by trailer sequence |
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Trailer Sequence |
Follows coding region after it ends with a stop codon; has terminator sequence used to stop transcription |
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Terminator Sequence |
Transcribed but no translated; found in trailer sequence |
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Transcription involves __, __, and ___ |
Initiation, Elongation, Termination |
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Operon |
sequence of bases in DNA that contains one or more structural genes together with the operator (binding site of protein) or activator-binding site controlling their expression |
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mRNA transcripts often encode > 1 proteins in bacteria |
A single promoter and terminator may flank multiple structural genes -> polycistronic arrangement |
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Operon Transcription |
- polycistronic mRNA encoding more than 1 protein - ensures that protein subunits making up a particular enzyme complex or required for a specific biological process are synthesized simultaneously and in correct stoichiometry - proteins require for uptake and metabolism of lactose are encoded by the lac Operon |
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Regulation of Gene Expression |
- bacteria adapt to their environment by controlling gene expression (ensures proteins/enzymes are only produced if required; conserves energy) |
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If bacteria encounter new source of carbon of nitrogen... |
They may switch on production of enzymes for new metabolic pathways enabling transport and use of the nutrient |
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If compounds are depleted from environment, bacteria... |
May switch on production of enzymes required to synthesize it "from switch" |
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Most Common Way of Altering Gene Expression is to Change Amount of mRNA transcription |
- efficiency of binding of RNA polymerase to promoter sites can altered in a number of ways: - environmental changes -presence or absence of regulatory proteins |
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Environmental changes can... |
Change extent of supercoiling of DNA; alters overall topology of promoters and efficiency of transcription initiation |
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Presence or Absence of Regulatory Proteins... |
Bind specifically to DNA adjacent to or overlapping the promoter site (operators); alter RNA polymerase binding and transcription |
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Operators (Operator Sites) |
Regions of DNA to which regulator proteins bind |
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2 Classes of Regulatory Proteins |
Activators: increase rate of transcription initiation Repressors: inhibit transcription |
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Genes subject to __ regulation need to bind __ protein(s) to stop transcription |
Negative, repressor |
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Genes subject to ___ regulation need to bind to __ protein(s) to initiate transcription |
Positive, activator |
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Regulon
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Genes and operons controlled by a common regulatory protein |
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lac Operon |
- codes for 3 enzymes necessary to utilize lactose - if glucose is present, the organism will preferentially use it over other sugars therefore no point in making enzymes necessary to use other sugars (like lactose) - under positive and negative control |
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lac Operon: Negative Control |
regulated by lac repressor which binds to operator when there is no lactose present |
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lac Operon: Positive Control |
regulated by catabolite activator protein (CAP) which binds to CAP site and cyclic AMP (cAMP) |
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Translation: Initial Complex |
mRNA, ribosome, initiator tRNA carrying formyl-methionine |
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Transcription |
- ribosomes bind to specific sequences in mRNA (Shine-Dalgamo) sequences and begin translation at AUG - polypeptide chain elongates as ribosome moves along RNA and carries out condensation reaction to couple incoming amino acids to the growing polypeptide chain - ends when ribosomes encounters either UGA, UAA, or UAG |
