Question

Ebola virus is a virus that is frequently and rapidly lethal in humans. The envelopes around particles of Ebola virus are studded with a viral glycoprotein (GP). Researchers hypothesized that, to enter a human cell, GP molecules must be cleaved by a protease enzyme, after which they bind with a protein called NPC1 in the human cell membrane. Reptile cells do not normally express the NPC1 protein, but the researchers modified some reptile cells to express NPC1. They then exposed the unmodified and modified cells to Ebola virus, both in the presence of a protease inhibitor that prevents GP cleavage, and without that inhibitor present. They then measured the frequency at which Ebola viruses infected the cells. These treatments are summarized below. I. Unmodified reptile cells, protease inhibitor absent II. Unmodified reptile cells, protease inhibitor present III. Modified reptile cells, protease inhibitor absent IV. Modified reptile cells, protease inhibitor present V. Unmodified human cells, protease inhibitor absent Of the following, which is a correct reason for including group V? :

(A) If the virus cannot enter group V but can enter group III, it shows that GP cleavage is not necessary for infection.

(B) If the virus can enter group V but cannot enter group IV, it shows that NPC1 is necessary for infection.

(C) If the virus can enter group V but cannot enter groups I, II, III, or IV, it shows that both GP cleavage and NPC1 are necessary for infection.

(D) Group V is a positive control.

Answer 1

Group V is taken as a positive control.

since, the virus can enter human cells, and we need to check its entry into reptile cells with different parameters, we need to consider a positive control.

for each and every experiment, one has to consider either a negative control or a positive control or both. a negative control is the one, which gives a negative result, i.e, we add everything except the protein or virus being tested. in this case, there would not be any reaction. however, a few cells may be lysed due to the chemicals or reagents we added. this particular number of cells should be subtracted from all the experimental sets since this number is not due to the protein or virus.

similarly, a positive control is the one, in which we observe the reaction or lysis. i.e, prior to the experiment, we know that this particular set gives a positive reaction. positive and negative controls are used to compare the results.

now,

option A- both group V and group III have NPCI and cleavage occurs in both the groups.

option B- both group V and group IV contain NPCI

option C- to show that both GP cleavage and NPC1 are necessary for infection, group III and group V both contain NPCI and cleavage occurs. if the virus enters these two groups but not other, then it indicates that both NPCI and cleavage are necessary.

so, the above options cannot differentiate the given statements.