At what enzymatic step in the citric acid cycle (Krebs cycle) does substrate level phosphorylation occur?
Correct Answer: B.Succinyl coenzyme A to succinate
There is only one step in the citric acid cycle that causes substrate level phosphorylation: the conversion of succinyl coenzyme A to succinate. GDP and inorganic phosphate combine to form GTP, which is roughly equivalent to the formation of one molecule of ATP. All others do not produce ATP. Oxaloacetate may be formed from pyruvate though it requires the dephosphorylation of one molecule of ATP. Moreover, this reaction is not considered one of the classic reactions in the citric acid cycle. In the conversion of malate to oxaloacetate, NAD+ loses a proton to form NADH.
The Medical College Admissions Test (MCAT) is a test administered by the Association of American Medical Colleges (AAMC). The test is designed to test your knowledge in three specific sections; physical sciences such as physics and general chemistry, biological sciences and organic chemistry, and verbal reasoning.
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The first question many people ask is, “when should I take the MCAT?” The general guideline is to take the MCAT the year before you plan to enter medical school. For example, the class of 2018 should take the MCAT sometime before or during the spring/summer of 2013. Your basic science coursework should be complete by this point.