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Biochem Ch. 19
Harvesting Electrons from the Citric Acid Cycle
| Question | Answer |
|---|---|
| What is another name for The Citric Acid Cycle? | TCA (Tricarboxylic Acid Cycle) or CAC (Carboxylic Acid Cycle) |
| What is the function of the Citric Acid Cycle? | to harvest high-energy electrons from carbon fuels (in the form of hydride ion, H-) |
| What are fuel molecules? | carbon compounds capable of being oxidized (losing electrons) |
| These fuel molecules are first processed to ___________ _____, the actual fuel for the citric acid cycle | acetyl CoA |
| The Citric Acid Cycle includes a series of oxidation-reduction reactions that ultimately result in what? | the oxidation of the acetyl group to two molecules of carbon dioxide |
| The Citric Acid Cycle consists of how many stages? | two |
| In the first stage of the Citric Acid Cycle, two carbons are introduced into the cycle, how? | by condensation of an Acetyl group with a four-carbon compound (oxaloacetate) |
| In the first stage of the Citric Acid Cycle, the condensation of an Acetyl group with oxaloacetate formed the six-carbon compound, ____________, which undergoes two ______________ _________________, generating 2 molecules of CO2 | Citrate, oxidative decarboxylations |
| In the second stage, ________________ is regenerated | oxaloacetate |
| In the second stage, oxaloacetate is regenerated, coupled with the formation of high-transfer-potential electrons (in the form of _______ and ________) and a molecule of _______. | NADH, FADH2, ATP |
| in both stages, electrons are removed that are then used for what? | they are used to power the synthesis of ATP in Oxidative Phosphorylation |
| The Citric Acid Cycle produces high-transfer-potential electrons, ATP, and Carbon Dioxide. What is the net reaction of the cycle? | Acetyl CoA + 3 NAD+ + FAD + ADP + P + 2H2O ---> 2CO2 + 3NADH + FADH2 + ATP + 2H+ + CoA |
| Stage 1 Summary: the cycle starts with the condensation of _______________ (C4) and _________ _____ (C2) to give __________ (C6) | oxaloacetate, Acetyl CoA, Citrate |
| Stage 1 Summary: Citrate (C6) is then isomerized to isocitrate.(C6) Why is this important? | isocitrate is a secondary alcohol which can be oxidized, wherease Citric Acid is a tertiary alcohol that cannot be oxidized further |
| Stage 1 Summary: oxidative decarboxylation of isocitrate (C6) gives ___-___________ (C5) | alpha-ketoglutarate |
| Stage 1 Summary: the second molecule of carbon dioxide comes off in the next reaction, in which alpha-ketoglutarate is oxidatively decarboxylated to ___________ _____ (C4) | succinyl CoA |
| Stage 2 Summary: The thioester of succinyl CoA is clreaved by orthophosphate to yield ___________, and a high-phosphoryl-treanser-potential compound in the form of ATP are also generated | succinate |
| Stage 2 Summary: Succinate is oxidized to ____________ (C4), which is then hydrated to form ___________ (C4) | fumurate, malate |
| Stage 2 Summary: Finally, malate is oxidezed to regenerate ______________ (C4). | oxaloacetate |
| Stage 2 Summary: 2 carbon atoms from acetyl CoA enter the cycle, and _#_ carbon atoms leave the cycle as CO2 in the successive decarboxylations | 2 |
| Stage 2 Summary: These successive decarboxylations are catalyzed by ______________ ______________ and ___-_________________ _____________. | isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase |
| Stage 2 Summary: In the fourth oxidation-reduction reactions in the cycle, 3 pairs of electrons are transferred to _____ and 1 pair to _____ (total of 8 electrons extracted from TCA cycle) | NAD+, FAD |
| Stage 2 Summary: These reduced electron carriers (NADH, FADH2) are subsequently oxidized by the electron-transport train to generate about how many ATP molecules? | 9 |
| Stage 2 Summary: How many molecules of ATP are gerated directly in the Citric Acid Cycle? | 1 |
| Stage 2 Summary: Hence, a total of _#_ ATP molecules are generated for each 2-Carbon fragment that is completely oxidized to H2O and CO2 | 10 |
| the key control point in the Citric Acid Cycle are the allosteric enzymes _____________ _____________ and ___-_________________ _____________ | isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase |
| The Citric Acid Cycle is regulated primarily by the concentrations of what? | ATP, NADH, ADP, etc (all allosteric modulators that work in same manner as previously examined) |
| Many of the components of the Citric Acid cycle are ______________ for biosynthesis of key biomolecules | precursors |
| Biosynthetic Precursors: Citrate is a precursor what what? (2) | fatty acids, sterols |
| Biosynthetic Precursors: alpha-ketoglutarate is a precursor what what? (3) | glutamate -> other amino acids -> purines |
| Biosynthetic Precursors: Succinyl CoA is a precursor what what? (3) | porphyrins, heme, and chlorophyll |
| Biosynthetic Precursors: Oxaloacetate is a precursor what what? | aspartate -> other amino acids, purines, pyrimidines |
| Biosynthetic Roles: When the energy needs of the cell are met, intermediates are replenished by the formation of _____________ from pyruvate | oxaloacetate |
| Because the Citric Acid Cycle provides precursors for biosynthesis, reactions to replenish the cycle components are required if the energy status of the cell changes. These replenishing reactions are called _________________ reactions | anapleurotic |
| A prominent anapleurotic reaction is catalyzed by _____________ ____________ | pyruvate decarboxylase (reaction used in gluconeogenesis and is dependent on the presence of acetyl CoA) |
| Defects in the Citric Acid Cycle, such as defects in succinate dehydrogenase, fumarase, or pyruvate dehydrogenase, can contribute to cancer. These defects contribute to the used of ___________ _____________ by cancer cells | aerobic glycolysis |
| Cancer cells exhibit no Pasteur Effect, which is what? | decreasing Glycolysis in the presence of oxygen |
Created by:
cmccartney2