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a. Trp operon is repressible because __.
b.__operon is usually off but
can be stimulated when specific small molecule interacts with regulatory
protein (ex: lac operon)
- its transcription is usually on but can be inhibited when specific small molecule binds allosterically to regulatory protein
- Inducible
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a. Lactose: i. Lactose metabolism: hydrolysis into __ and __ by __
1. Only a few molecules of this enzymes are present in E. coli cell growing in absence of lactose
a. If added, number of __increases a thousandfold
- glucose and galactose
- beta-galacosidase
- beta-galactosidase
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i. __ is part of lac operon, which includes two other genes coding for enzymes that function in lactose utilization
1. Entire transcription unit under command of __
a. The regulatory gene, lacI, located outside the operon, codes for an Allosteric repressor protein that can do what?
- Beta-galactosidase
- one main operator and promoter
- switch off the lac operon by binding to operator
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i. Difference between lac and trp
- 1. Trp is inactive by itself and requires tryptophan as a corepressor in order to bind to operator
- 2. Lac repressor is active by itself, binding to operator and switching the lac operon off
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a. Inducer __the repressor i. For lac operon, it is __
ii. In absence of lactose and hence allolactose, the lac repressor is in its __, and genes of lac operon are __
- inactivates
- allolactose
- active configuration
- silenced
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1. If lactose added, allolactose __
a. Without bound repressor, the lac operon is transcribed into mRNA for the lactose-utilizing enzymes
binds to the lac repressor and alters its conformation, nullifying the repressor’s ability to attach the operator
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1. the enzymes of the lactose pathway= __enzymes because their synthesis is __by a chemical signal
- the enzymes for tryptophan synthesis are said to be __
- inducible
- induced
- repressible
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1. repressible enzymes generally function in __pathways, which synthesize essential end products from raw materials
a. by suspending production of an end product when it is already present in excess, the cell can __
- anabolic
- allocate its organic precursors and energy for other uses
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1. in contrast, inducible enzymes usually function in __pathways, which break down a nutrient to simpler molecules
a. by producing the appropriate enzymes only when the nutrient is available, __
- catabolic
- the cell avoids wasting energy and precursors making proteins that are not needed
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a. regulation of both the trp and lac operons involves __control of genes, because the operons are switched off by the active form of the repressor protein i. for lac, it is __because allolactose induces enzyme synthesis not by acting directly on the genome, but by freeing the lac operon from the negative effect of the repressor
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when does positive only occur?
a. positive only occurs when regulatory protein interacts directly with genome to switch transcription on
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