The promoter of the araBAD operon from E. coli is activated in the presence of arabinose and the absence of glucose and directs expression of genes encoding enzymes required for arabinose metabolism. Unlike the cases of lac and gal genes, where a repressor and an activator work together, here two activators work together: AraC and CAP

+ arabinose	AraC binds that sugar and adopts a configuration that allows it to bind DNA as a dimer to the adjacent half-sites, araI1 and araI2
– arabinose	the AraC dimer adopts a different conformation and binds to araO2 and araI1, there is no monomer at site araI2, and so the protein cannot activate the araBAD promoter (araPBAD). This promoter is also controlled by CAP.

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#Question id: 6943

#Unit 5. Developmental Biology

The portion of the blastoderm-stage embryo which will give rise to most ectodermal, mesodermal, and endodermal tissues is called the:

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#Question id: 2142

#Unit 2. Cellular Organization

Glucose transport into erythrocytes is an example of

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#Question id: 4195

#Unit 3. Fundamental Processes

Unlike bacterial mRNA, eukaryotic mRNA must undergo __ before it may be used for translation.

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#Question id: 1360

#Unit 4. Cell Communication and Cell Signaling

Plasmodesmata of plant cells have .........in common with gap junctions in animal cells, but have .......... that gap junctions lack.

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#Question id: 5934

#General Aptitude

September 13 , 1992 was a Sunday . Then which of the following is true ?