llUlllllllllld hydrogen d. Ethanal and methanol 21. In the Krebs cycle, isocitra
ID: 1062914 • Letter: L
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llUlllllllllld hydrogen d. Ethanal and methanol 21. In the Krebs cycle, isocitrate is oxidized by NAD then undergoes decarboxylation to a-ketoglutarate. How does the NAD" oxidation prepare the molecule for the subsequent decarboxylation? pyttNate CoA Ho-de-ooo' oxaloacetate citrate malate KREBS CYC NADH H", cor E fumarate FAD succinate ATF a. It forms a carboxy-group b. It introduces a C O group to the a-position of a carboxy-group c. It introduces a C o group to the B-position of a carboxy-group d. It increases nucleophilicity of NAD e. It increases electrophilicity of NAD 22. Based on your answer to question 21, which part of the isocitrate molecule becomes the molecule of Co that we exhale? a. The carboxy-group on the top of the molecule b. The carboxy-group on the right of the molecule c. The carboxy-group on the bottom of the molecule d. The co group produced as a result of oxidation The CH2-groupExplanation / Answer
21. it introduces C=O group to alpha position of carboxyl group and this is explainedhere detailed, Within the citric acid cycle, isocitrate, produced from the isomerization of citrate, undergoes both oxidation and decarboxylation. Using the enzyme Isocitrate Dehydrogenase (IDH), isocitrate is held within its active site by surrounding arginine, tyrosine, asparagine, serine, threonine, and aspartic acid amino acids. The first box shows the overall isocitrate dehydrogenase reaction. The reactants necessary for this enzyme mechanism to work are isocitrate, NAD+/NADP+, and Mn2+ or Mg2+. The products of the reaction are alpha-ketoglutarate, carbon dioxide, and NADH + H+/NADPH + H+. Water molecules are used to help deprotonate the oxygens (O3) of isocitrate. In the Step 1, which is the oxidation of the alpha-C (C#2).Oxidation is the first step that isocitrate goes through. In this process, the alcohol group off the alpha-carbon (C#2) is deprotonated and the electrons flow to the alpha-C forming a ketone group and removing a hydride off C#2 using NAD+/NADP+ as an electron accepting cofactor. The oxidation of the alpha-C allows for a position where electrons (in the next step) will be coming down from the carboxyl group and pushing the electrons (making the double bonded oxygen) back up on the oxygen or grabbing a nearby proton off a nearby Lysine amino acid. In Step 2, which is the decarboxylation of oxalosuccinate. In this step, the carboxyl group oxygen is deprotonated by a nearby Tyrosine amino acid and those electrons flow down to carbon 2. Carbon dioxide leaves the beta carbon of isocitrate as a leaving group with the electrons flowing to the ketone oxygen off the alpha-C placing a negative charge on the oxygen of the alpha-C and forming an alpha-beta unsaturated double bond between carbons 2 and 3. The lone pair on the alpha-C oxygen picks up a proton from a nearby Lysine amino acid. In Step 3, which is the saturation of the alpha-beta unsaturated double bond between carbons 2 and 3. In this step of the reaction,[5][6] Lysine deprotonates the oxygen off the alpha carbon and the lone pair of electrons on the oxygen of the alpha carbon comes down reforming the ketone double bond and pushing the lone pair (forming the double bond between the alpha and beta carbon) off, picking up a proton from the nearby Tyrosine amino acid. This reaction results in the formation of alpha-ketoglutarate, NADH + H+/NADPH + H+, and CO2[3].
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