DAT Question of the Day

Correct Answer: D. complementary DNA

The genomic library of an organism can be created by using complementary DNA (cDNA). cDNA is synthesized from messenger RNA using reverse transcriptase. Genomic libraries made using cDNA are not complete as the messenger RNA that is transcribed is not an exact complement to the original DNA strand due to the absence of introns.

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Correct Answer: A. moves 3 Na⁺ out and 2 K⁺ in the cell

Maintenance of the cell membrane potential is conducted by keeping a low concentration of Na ions and high concentration of K ions inside the cell. The pump uses ATP energy to expel three Na ions out of the cell. Also, the pump enables entrance of two K ions into cell. However, the resting potential of the membrane IS NOT as a result of pumping out 3 positive ions and only pumping in 2 positive ions. The resting potential is achieved due to the impermeability of the membrane to the ions.

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Correct Answer: C. depolarization of the beta cell membrane leads to an increased level of intracellular Ca2+

To begin, glucose is transported into the beta cell. As a result of glucose metabolism, ATP molecules are generated. An increased level of ATP inhibits the KATP channel, preventing entrance of K⁺ ions into the cell. The consequence of this action is depolarization of the cell membrane and subsequent activation of the VDCC. Ca²⁺ ions enter into the cell stimulating exocytosis of insulin. This is a great example of an application question in the biology section of the DAT.

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