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?
(a) Because it acts on so many diverse cell types, QGF probably diffuses across the plasma membrane into the cytoplasm of these cells.
(b) Glial cells do not have a receptor for QGF.
(c) QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed.
(d) Heart muscle cells, fibroblasts, and nerve cells must all have the same receptor for QGF.
Choice (c) is most likely to be true. Because heart muscle cells, fibroblasts, and nerve cells all respond to QGF with different outcomes, it is likely that QGF activates different effector proteins in these different cell types, leading to the diversity of outcomes observed in the experiment. QGF is unlikely to diffuse across the cell membrane, given that it is a large protein [choice (a)]. Although glial cells do not die or divide in response to QGF, they could have a receptor for QGF, as receptor activation could lead to some other response [choice (b)]. A signal molecule can often bind to different types of receptor on different cell types, so choice (d) may or may not be correct.
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mechanisms is
a. glucagon. b. insulin. c. adenylyl cyclase. d. cyclic AMP. e. mRNA.
In response to temperature changes, cell membranes change state to become more solid or more fluid by undergoing
A) lipid raft formation. B) membrane folding. C) a phase transition. D) transverse diffusion. E) differential scanning calorimetry.
During what step of glycolysis are two ATP molecules required?
A. pyruvate formation B. cleavage and rearrangement C. oxidation D. acetyl-CoA formation E. glucose priming
Choose the true statements about the evolution of larval dispersal in marine snails.
A. Cladistics shows that there are more instances of the transition from dispersing to non-dispersing larvae than the reverse. B. Loss of structures in the transition from dispersing to non-dispersing may inhibit evolutionary reversal. C. Possession of dispersing larvae is the ancestral state in snails. D. The evolution of non-dispersing snails is likely to hinder speciation. E. Clades of non-dispersing snails are less species rich than those of dispersing snails.