The lab you work in has discovered a previously unidentified extracellular signa
ID: 86501 • Letter: T
Question
The lab you work in has discovered a previously unidentified extracellular signal molecule called QGF, a 75,000-dalton protein. You add purified QGF to different types of cells to determine its effect on these cells. When you add QGF to heart muscle cells, you observe an increase in cell contraction. When you add it to fibroblasts, they undergo cell division. When you add it to nerve cells, they die. When you add it to glial cells, you do not see any effect on cell division or survival. Given these observations, which of the following statements is most likely to be true?. Because it acts on so many diverse cell types, QGF probably diffuses across the plasma membrane into the cytoplasm of these cells. Glial cells do not have a receptor for QGF. QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed. Heart muscle cells, fibroblasts, and nerve cells must all have the same receptor for QGF. Acetylcholine is a signaling molecule that elicits responses from heart muscle cells, salivary gland cells, and skeletal muscle cells. Which of the following statements is false? Heart muscle cells decrease their rate and force of contraction when they receive acetylcholine, whereas skeletal muscle cells contract. Heart muscle cells, salivary gland cells, and skeletal muscle cells all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family. Active acetylcholine receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways. Heart muscle cells, salivary gland cells, and skeletal muscle cells all respond to acetylcholine within minutes of receiving the signal. The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by ________________. activating a G-protein activating a receptor tyrosine kinase diffusing into cells & stimulating the cyclase directly activating an intracellular protein kinase Figure Q16-15 shows the pathway through which nitric oxide (NO) triggers smooth muscle relaxation in a blood-vessel wall. Which of the following situations would lead to relaxation of the smooth muscle cells in the absence of acetylcholine? A smooth muscle cell that has a defect in guanylyl cyclase such that it cannot bind NO a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to cyclic GMP a muscle cell that has cyclic GMP phosphodiesterase constitutively active a drug that blocks an enzyme involved in the metabolic pathway from arginine to NOExplanation / Answer
16-10. Ans: b. Glial cell does not have a receptor for QGF. &
c. QGF activates different intra cellular pathways in heart, muscle and fibroblast cells to produce different respond.
Because it is difficult for a 75 kDa passes through the membrane by diffusion and if that so then it must has some effects on Glial cell also. More over it is not necessary that QGF must work through the same receptor pathway. Same ligand can be acts with different nearly similar receptor. However, it is quite possible QGF acts through different pathway in different cell and none of them are present on glial cells.
16-12.Ans. D. Heart muscle, skeletal muscle, salivary gland cells all responds to acetylcholine within minutes of receiving of signal.-False
They responds in a millisecond time duration.
16-14. Ans. The local mediator NO stimulates the intracellular enzyme guanylyl cyclase by
C. diffusing into cells and stimulating the cyclase activity.
16-15. Ans: C. A muscle cell that has a defect in guanyl cyclase such that it constitutively converts GTP to cGMP.
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