Gene structure and expression in prokaryotes THE LAC and TRP OPERON L1

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  • Created by: Alex
  • Created on: 12-04-13 13:16
Operon
In prokaryotes, a group of structrual genes that are coordinately controlled and transcribed as a single message, plus their adjacent regulatory elements
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LActose Catabolism definition
set of metabolic pathways that breaks down lactose molecules into smaller units(glucose and galactose) and release energy
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Is lac operon always functioning
No can be switched on and off - only works when lactose is present in growth medium
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Catabolite repression
In the presence of lactose and a better energy source, such as glucose, the bacteria will use only glucose.
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Diauxic growth
Double growth. 2 sugars on growth media, 1 easier for bacterium to metabolize -consumed 1st, causes rapid growth. Followed by lag phase, cellular machinery used to metabolize 2nd sugar activated. Bacterium has slower growth phase- 2nd sugar metabolis
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Lac Genes/Cistrons
LacI gene, LacY cistron, LacZ cistron, LacA cistron
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What is the difference between a cistron and a gene?
Cistrons encode only a single protein - they don't have their own individual promoters or terminators. Genes code for both proteins and functional RNA.
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Lac I gene
Regulatory Gene - produces repressor protein that controls the operon(not part of operon - has own promoter)
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Lac Y cistron
Encodes lactose permease that transports lactose into the cell
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Lac Z cistron
Encodes Beta-galactosidase - enzyme that catalyses the breakdown of lactose to glucose and galactose
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Lac A cistron
Encodes lactose transacetylase - unclear function
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When lactose is present
Operon is activated
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Lac Repressor Role
prevents RNA polymerase binding and unwinding DNA to get template
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trp Operon
produces anabolic enzymes - that synthesise tryptophan - inactive in presence of tryptophan
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When tryptophan is present
Tryptophan binds to TrpR repressor forming a complex which binds to the operator region preventing more tryptophan being synthesised.
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Card 2

Front

LActose Catabolism definition

Back

set of metabolic pathways that breaks down lactose molecules into smaller units(glucose and galactose) and release energy

Card 3

Front

Is lac operon always functioning

Back

Preview of the front of card 3

Card 4

Front

Catabolite repression

Back

Preview of the front of card 4

Card 5

Front

Diauxic growth

Back

Preview of the front of card 5
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