Nitrogen gas is first converted into _____ by certain_____ before it enters the land nitrogen cycle
a. nitrate; bacteria
b. ammonium; bacteria
c. elemental nitrogen; bacteria
d. nitrate; bacteria and fungi
e. ammonium; bacteria and fungi
ANSWER: b
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The deactivation of NK cells due to binding of NK receptors to MHC I proteins is called
A) promoting. B) phagocytosis. C) licensing. D) neutralization.
What event typically begins in anaphase and is completed soon after the end of telophase?
A) interphase B) packing of DNA into well-defined chromosomes C) cytokinesis D) alignment of chromosomes at the cell equator
A hybrid zygote created by the fusing of gametes from different species may grow into a sterile adult incapable of producing future offspring. This is an example of__________
What will be an ideal response?
The yeast GAL4 gene encodes a transcriptional regulator that can bind DNA upstream of genes required for the metabolism of the sugar galactose and turn them on. Gal4 has a DNA-binding domain and an activation domain
The DNA-binding domain allows it to bind to the appropriate sites in the promoters of the galactose metabolism genes. The activation domain attracts histone-modifying enzymes and also binds to a component of the RNA polymerase II enzyme complex, attracting it to the promoter so that the regulated genes can be turned on when Gal4 is also bound to the DNA. When Gal4 is expressed normally, the genes can be maximally activated. You decide to try to produce more of the galactose metabolism genes by overexpressing the Gal4 protein at levels fiftyfold greater than normal. You conduct experiments to show that you are overexpressing the Gal4 protein and that it is properly localized in the nucleus of the yeast cells. To your surprise, you find that too much Gal4 causes the galactose genes to be transcribed only at a low level. What is the most likely explanation for your findings?