54. You learned in lecture and in an NPR radio clip that size variations in dogs
ID: 73945 • Letter: 5
Question
54. You learned in lecture and in an NPR radio clip that size variations in dogs can be caused by differences in insulin-like growth factor IGF1. Which of the following is NOT true of IGFs? A) they activate RTKs B) they cause the secretion of growth hormone C) they can act as paracrine signaling molecules D they simulate a phosphorylation cascadeing MAPinases 55. Tadpoles must unde rgo a major metamorphosis to become frogs. This change includes reabsorption of the tail, growth of limbs, calcification of the skeleton, increase in rhodopsin in the eye, d change in hemoglobin structure, and reformation of the gut from the long gut of an herbivore to the short gut of a carnivore. Amazingly, all of these chang for such a wide array of effects of thyroxine? A) Some tissues have membrane receptors for thyroxine, while other tissues have thyroxine receptors within the mbs, calcification of the skeleton, increase in rhodopsin in the eye, development of lungs es are induced by thyroxine. What is the most likely explanation nucleus. B) There are many different forms of thyroxine, each specific to a different tissue C) Different releasing hormones release thyroxine to different tissues D) Different tissues have thyroxine receptors that activate different signal transduction pathways 56. Testosterone is an example of a chemical signal that affects the very cells that synthesize it, the neighboring cells in the testis, along with distant cells outside the gonads. Thus, testosterone is an example of I) an autocrine signal Il) a paracrine signal III) an endocrine signal A) only I and ill B) only II and Ill C) only I and I D) 1,11, and III 57. In experiments where researchers suspect that a hormone may be responsible for a certain physiological effect, they may cut the neurons leading to the organ where the effect being studied occurs. What is the purpose of cutting these neurons? A) to make sure that the organ being affected cannot function unless the researchers stimulate it with an external electrical probe B) to impair the normal functions of the organ so that the hormonal effect can be more easily studied C) to numb the organ so that it can be probed without inducing pain in the lab animal D) to make sure that the effect is not occurring through actions in the nervous system 58. Testosterone and estrogen are lipid-soluble signal molecules that cross that plasma membrane by simple diffusion. If these molecules can enter all cells, why do only specific cells respond to their presence? A) Non-target cells lack the inactive enzymes that the signal molecule activate B) Non-target cells lack the intracellular receptors that, when activated by the signal molecule, can interact with genes in the cell's nucleus C) Non-target cells possess enzymes that immediately degrade the molecules as they enter the cell D) The signal molecules diffuse from the cell before an effective concentration can be achieved 59. An example of antagonistic hormones controlling homeostasis is A) insulin and glucagon in glucose metabolism B) epinephrine and norepinephrine in fight-or-flight responses C) progestins and estrogens in sexual differentiation D) thyroxine and parathyroid hormone in calcium balance 60. Analysis of a blood sample from an individual who had eaten 10 minutes ago would be expected to reveal high levels of A) glucagon B) insulin C) sucrose D) gastrin Page 8 of 22Explanation / Answer
54.
Insulin like growth factor (IGF) is signalling molecule that activates the receptor through recptor tyrosine kinase (RTK), it acts through paracrine signalling and stimulates the growth hormone. IGF activates intracellular signalling cascade like phosphatidylinositol3(PIP3). Hence, option D is correct.
55.
The hormone thyroxine (T4) plays a major role in development and metamorphosis of tadpole into frog. The thyroxine hormone produces organ specific signalling in different tissues with thyroxine receptors triggering different signal cascades. Hence, option D is correct.
56.
Testosterone or male sex hormone stimulate the testis and near by cells and distant cells as well. Therefore testosterone is an example of autocrine, paracrine and endocrine hormone. Hence, option D is correct.
57.
When the neurons carrying a specific hormone to a specific organ is cut so that the function of hormone and organ are well studied and the organ is affected till the external signal stimulate the organ as a hormone so that the role of hormone in the function of organ can be known. Hence, option B is correct.
58.
Nontarget cells do not posess the intracellular receptors for the specific signal molecule (hormone) so that they interact wth them to produce a required response. Hence, option B is correct.
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