Wild type E. coli metabolizes the sugar lactose by expressing the enzyme ß-galactosidase. You have isolated a mutant that you call lac1–, which cannot synthesize ß-galactosidase and cannot grow on lactose (Lac–). During an condition you have a wild type (Lac+) strain carrying a Tn5 insertion known to be near several Lac genes on the E. coli chromosome. You grow P1 phage on this strain and use the resulting phage lysate to infect the lac1– strain, selecting for kanamycin resistance (Kanr). Among 100 Kanr transductants, you find that 82 are Lac– and 18 are Lac+. Express the distance between Tn5 and the lac1– mutation as a cotransduction frequency;

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#Question id: 12179

#Unit 2. Cellular Organization

Match the following human ABC proteins (Column I) with their function (Column II)

Column I	Column II
A. ABCB1	i. Transports Cl- ions
B. ABCB4	ii. Exports phosphatidylcholine into bile
C. CFTR	iii. Exports cholesterol and phospholipid for uptake into high-density lipoprotein (HDL)
	iv. Exports lipophilic drugs

Which of the following is correct?

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#Question id: 12180

#Unit 2. Cellular Organization

Following statements are regarding to cotransport.

A. The two forces constituting the electrochemical gradient—the membrane electric potential and the ion concentration gradient—may act in the same or opposite directions.

B. Cotransporters use the energy released by movement of an ion (usually H+ or Na+) down its electrochemical gradient to power the import or export of a small molecule or different ion against its concentration gradient.

C. Cotransporters use the energy released by movement of an ion (usually H+ or Na+) down its electrochemical gradient to power the import or export of a small molecule or different ion down its concentration gradient.

D. The cells lining the small intestine and kidney tubules contain symporters that couple the energetically favorable entry of Na+ to the import of glucose against its concentration gradient.

Which of the following is incorrect?

TLS Online TPP Program

#Question id: 12181

#Unit 2. Cellular Organization

Following statements are regarding to the CFTR.

A. cystic fibrosis transmembrane conductance regulator allows Cl− ions to flow out of the cell, following their concentration gradient.

B. ATP binding to CFTR’s two nucleotide-binding domains appears to close the Cl− channel, and the hydrolysis of one ATP opens it (the other ATP remains intact).

C. the CFTR channel can open only if its regulatory domain (which is unique among ABC transporters) has been phosphorylated, thus regulating the flow of ions across the membrane.

D. The maintenance of electrical neutrality requires that the Cl− ions transported by the CFTR be accompanied by positively charged ions, mainly Na+. The transported ions are osmotically accompanied by water, thus maintaining the proper level of fluidity in secretions of the airways, intestinal tract, and the ducts of the pancreas, testes, and sweat glands.

Which of the following combination is correct?

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#Question id: 24651

#Unit 2. Cellular Organization

For the SERCA pump, how many Ca2+ ions moves across the membrane during each catalytic cycle ?

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#Question id: 24652

#Unit 2. Cellular Organization

The mechanism postulated for P-type ATPases takes into account the large conformational changes and the phosphorylation dephosphorylation of the critical:

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#Question id: 24653

#Unit 2. Cellular Organization

Which of the following membrane protein form channel, in the form of gap junctions between cells?