zuai-logo
zuai-logo
  2. AP Biology
FlashcardFlashcardStudy GuideStudy GuideQuestion BankQuestion Bank
GlossaryGlossary

Cell Communication and Cell Cycle

Question 1
2022BiologyAPConcept Practice
12 marks

The binding of an extracellular ligand to a G protein-coupled receptor in the plasma membrane of a cell triggers intracellular signaling (Figure 1, A). After ligand binding, GTP replaces the GDP that is bound to Gsa, a subunit of the G protein (Figure 1, B). This causes Gsa to activate other cellular proteins, includin...

1.a) A membrane is hydrophobic and requires a channel for chloride ions to pass through. The movement of chloride ions out of the intestinal cells increases the solute concentration outside the cells. This causes water to move out of the cells by osmosis, leading to water loss.

3 marks

1.b) An independent variable in the experiment is the presence or absence of cholera toxin. A negative control in the experiment is Sample I. The scientists included Sample III as a control treatment to determine the effect of cholera toxin alone on cAMP production, without the presence of GTP.

3 marks

1.c) Based on the data, cholera toxin increases the synthesis of cAMP. The percent change in the rate of cAMP production due to the presence of cholera toxin in sample IV compared with sample II is calculated as follows:
((127.0 - 10.0) / 10.0) * 100 = 1170%.

3 marks

1.d) If the drug binds to all of the toxin, the rate of cAMP production would be similar to the rate in sample II, which is 10.0 pmol per mg adenylyl cyclase per min. The claim that cholera toxin will not cause excessive water loss from whole intestinal cells that contain the mutant adenylyl cyclase is justified because the mutant adenylyl cyclase cannot be activated by Gsa, and therefore, the cholera toxin will not be able to cause excessive cAMP production.

3 marks
Feedback stars icon

How are we doing?

Give us your feedback and let us know how we can improve