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BIOL 112 Chapter Notes - Chapter 17: Tryptophan, Trp Operon, Lac Repressor

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blushmule307
6 Apr 2012
School
UBC
Department
Biology
Course
BIOL 112
Professor
Karen Smith

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BIOL 112 Full Course Notes
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BIOL 112 Full Course Notes
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Document Summary

Dna mrna protein activated protein: transcriptional control: dna x-> mrna (slowest, most effective-no use of energy, translational control: mrna x-> protein, post-translational control: protein x->activated protein (fastest, lots of energy needed) Constitutively: all the time, referring to genes that are transcribed all the time. 17. 2 identifying the genes involved in lactose metabolism. Laci: regulatory protein to allow a set of genes to be transcribed. 17. 3 mechanisms of negative control: discovery of the repressor. Negative control: regulatory protein binds to dna (upstream the promoter) and shuts down transcription, it must be taken away for transcription to occur. Laci gene = repressor as it exerts negative control over lacz and lacy to inhibit transcription. Operon: a region of prokaryotic dna that codes for serious of functionally related genes and is transcribed from a single promoter into a polycistronic mrna. When there is no lactose present there is no need for the proteins to catabolize it so the laci binds to.

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Related Questions

1. The lac operon of E. coli controls the expression of genes that code for enzymes involved in lactose metabolism. The operon system is inducible in that it can be ‘turned on’ by the presence of lactose. Mutations to various regions of the lac operon have been discovered which affect both the control of gene expression and the function of the gene products.

These mutations include:

I - = produces a repressor protein that can not bind to the operator region

I s = produces a repressor protein that can not be removed from the operator region

O C = can not bind a repressor protein

Z - = produces a defective (non-functioning) β-galactosidase enzyme

( I- are recessive to I+; I+ recessive to IS )

Detail the functionality of the lac

operon under the following genetic and cellular conditions.

GENES

Lactose

present

Repressed

(yes/no)

Constitutive

(yes/no)

Inducible

(yes/no)

I + O + Z +

no

I + O C Z +

no

I S O + Z +

yes

I - O + Z +

yes

I S O C Z +

no

When (glucose, lactose) ___________ levels inside a bacterial cell are low, cyclicAMP levels are (high, low) __________. This is because metabolizes sugars (activate, inhibit) ___________ the enzyme adenylate cyclase, and (activate, inhibit) __________ the enzyme cAMP phosphodiesterase, causing cyclic AMP levels to rise. Consequently, the CAP protein is (Activated, inhibited, unaffected) ___________ by the cyclic AMP and binds to the lac promoter region, and the CAP protein acts like a sigma factor recruiting (DNA, RNA) ___________ polymerase to the promoter. This establishes condition that may lead to the (transcription, replication) __________ of the lac operon if (allolactose, glucose, lactose) _____________ is available to bind to (lac repressor, lacZ, lacY, lacA) _________ protein keeping this protein from binding to the (lacO, lacZ. lacY, lacA) ___________ gene.

1.In the bacterial lac repressor, which of these occurs:

A.In the presence of glucose and the absence of lactose, the repressor is actively produced.

B.The lac operon can be hyper-induced in the presence of low glucose by the 'cAMP binding protein' (CAMP).

C.In the presence of lactose and the absence of glucose the lac operon is repressed.

D.Allolactose is a byproduct of β-galactosidase, indicating high lactose when it builds up.

2 In eukaryotes the enhancer elements can be quite a distance upstream or downstream from the promoter, and transcriptional regulation is helped by protein:protein interactions.

True

False