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What are gratuitous inducers?
- -chemical analogs similar to the natural compounds
- -do not act as a substrate for the enzyme
- -ex: Isopropylthiogalactoside (IPTG), can take the place of lactose
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When do you get an expression of lac operon?
- Glucose levels down
- lactose levels up
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When do you get no expression of lac operon?
- Glucose levels up
- Lactose levels down----> no transcription
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What enzyme does lac Z code for?
- Beta-galactosidase
- -converts lactose into galactose and glucose
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What enzyme does lac Y code for?
- Permease
- -facilitates the entry of lactose into the bacterial cell
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What enzyme does lac A code for?
- Transacetylase
- -remove toxic bystanders
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What is TrpR-?
- A mutation, a repressor, and won't bind
- No transcription when present
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Where is the TATA box?
25-30 bp upstream
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What is the TATA box?
A promoter
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What are the structural motifs of DNA-binding proteins?
- -Helix-turn-helix
- -Zinc finger
- -Basic leucine zipper
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Helix-turn-helix
a motif present in eukaryotic and prokayotic transcription factors that have two adjacent alpha-helices separated by a turn of several AA
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Zinc finger
a class of DNA-binding domains found in proteins containing a characteristic pattern of cysteine and histidine residues that complex with zinc ions, creating finger-like structures
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Basic leucine zipper
a motif that allows protein-protein dimerization, which includes two basic alpha-helical regions adjacent to the zipper that bind to phosphate residues and specific bases in DNA
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Why do we have multiple protein products?
Alternative splicing: generation of different protein molecules from the same pre-mRNA by changing the number and order of exons in the mRNA product
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Eukaryotic vs. Prokaryotic regulation of gene expression:
- Eukaryotes have pre and post transcription
- more DNA
- mRNAs must be spliced, capped, and polyadenylated before going to nucleus
- genetic info carried on many chromosomes (not just one)
- mRNAs have a wide range of half life
- translation rates can be modulated
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What are some characteristics of enhancers?
- Can be located on:
- either side of the gene
- some distance from the gene
- even within the gene
- upstream, down stream from the gene
are cis-regulators because they function when adjacent to the structural gene they regulate
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What is cAMP?
A molecule that binds to CAP, in order for it to bind to the lac operon promoter
When glucose is present, cAMP levels decrease, so can't bind to to lac operon, so no transcription and translation
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Name a trans-acting regulator:
transcription factors
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What is a PIC?
- Pre-initiation complex
- -required for initiation of transcription by RNA pol II
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What is the function of RISC?
an antisense siRNA or miRNA associates with this enzyme complex which then seeks complementary mRNA and cleaves them or associates with them to prevent translation
chops it up
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What is the function of RITS?
- Chromatin remodeling
- Transcription silencing
- binds in the genome, and shuts off any RNA being made
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What is RNAi?
inhibition of gene expression in which a protein complex containing a partially complementary RNA strand binds to an mRNA, leading to degradation or reduced translation of the mRNA.
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