![]() GAP removes an inorganic phosphate which is the function of a phosphatase.Ĥ) The second paragraph begins with “ ADP-ribosylation factor I (Arf1) plays an essential role in vesicle formation and is responsible for the recruitment of cytosolic coat protein complexes (COPs) and subsequent retrograde transport from the Golgi apparatus.” Isomerase – An isomerase alters the structural arrangement of its substrate.Kinase – Kinases phosphorylate their target GAP does the opposite and removes the phosphate.GAP removes an inorganic phosphate and is indeed a phosphatase. Phosphatase – A phosphatase cleaves a phosphate bond to remove a phosphate from its target.GAP catalyzes the removal and release of a phosphate, not its transfer. Transferase – A transferase transfers a functional group from one molecule to the next.GTP is most closely related to nucleotides.ģ) The passage states the following: “ GTPase activating protein (GAP) catalyzes the conversion of Arf1-bound GTP to GDP and inorganic phosphate, thereby converting the protein to the inactive form.” Carbohydrate – Some of the most notable examples of carbohydrates on the MCAT are glucose, lactose and sucrose, none of which resemble an entire GTP molecule.Lipids – Lipids are fats with plenty of hydrocarbons, not seeing much of that in GTP.Amino acids – You should have the structure of each of the amino acids memorized by test day.GTP is analogous to AMP but with two additional phosphates and a guanine instead of an adenine. Nucleotides – AMP, seen above, is a nucleotide.Take a look at the structure of AMP in preparation for the answer choices. Answer choice C is the correct answer.Ģ) This question is a pseudodiscrete. – If you were tempted by this answer, you were probably thinking about the sentence that says “ Upon GTP exchange, Arf1 undergoes a conformational change that releases the myristoylated N -terminus of the polypeptide chain from a structural groove in the protein and initiates localization to phospholipid bilayers.” However, the GTP exchange the sentence is referring to is the exchange of GDP for GTP which is the opposite of what is asked in the question stem would cause the protein to become activated. The conversion of GTP to GDP when bound to Arf1 promotes its inactivation. The protein is inactivated, not activated. – This is the opposite of what the author says in the passage. We are simply told that it is converted to the inactive form, not that it unfolds. – Denaturation would imply that Arf1 unfolds when GTP is hydrolyzed to GDP. “ The Arf1 GTPase activating protein (GAP) catalyzes the conversion of Arf1-bound GTP to GDP and inorganic phosphate, thereby converting the protein to the inactive form.” This passage was quite dense, but we can use the following information from the end of paragraph 2 to answer the question. ![]() Sample Test Biology/Biochemistry Section Passage 1ġ) To start us off on the bio/biochem section of the Sample test, we’re being asked to consider the effect of GTP hydrolysis to GDP when bound to Arf1.
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