Citric Acid Cycle Quiz: Check your Krebs cycle knowledge
This citric acid cycle quiz helps you review each step of the Krebs cycle and see how carbon, energy carriers, and ATP connect. Use it to check what you know before class or an exam, then deepen your practice with the glycolysis pathway quiz, explore a broader biochemistry quiz, or switch it up with a krebs cycle game.
Study Outcomes
- Recall Key Intermediates -
Identify and memorize the main substrates and products in each step of the citric acid cycle quiz to reinforce your metabolic pathway knowledge.
- Explain Enzymatic Roles -
Describe the function of critical enzymes in the TCA cycle quiz and how they facilitate energy production during cellular respiration.
- Analyze Regulatory Mechanisms -
Examine the control points within the Krebs cycle quiz to understand how flux is adjusted in response to cellular energy demands.
- Apply Metabolic Integration -
Connect the citric acid cycle game to glycolysis and the electron transport chain to see how carbon flow affects overall ATP yield.
- Predict Pathway Outcomes -
Use quiz scenarios to anticipate changes in metabolite levels under varying conditions, such as high NADH or low oxygen.
- Evaluate Energy Yield -
Calculate the net production of NADH, FADHâ‚‚, and GTP per cycle turn to gauge the efficiency of cellular respiration.
Cheat Sheet
- Entry of Acetyl-CoA and Citrate Formation -
Acetyl-CoA condenses with oxaloacetate via citrate synthase to form citrate in a highly exergonic reaction (Nelson & Cox, Lehninger Principles). This committed step drives the TCA cycle forward and is tightly regulated to match cellular energy demand.
- Oxidative Decarboxylation Steps -
Isocitrate dehydrogenase converts isocitrate to α-ketoglutarate, releasing CO₂ and reducing NAD⺠to NADH, followed by α-ketoglutarate dehydrogenase generating succinyl-CoA, another CO₂, and NADH (Alberts et al., Molecular Biology of the Cell). These two key steps account for two of the cycle's three NADH-producing oxidations.
- Substrate-Level Phosphorylation and GTP/ATP Generation -
Succinyl-CoA synthetase catalyzes the conversion of succinyl-CoA to succinate, coupled to GTP (or ATP) formation via nucleoside diphosphate kinase, representing the sole substrate-level phosphorylation in the TCA cycle (Voet & Voet, Biochemistry). This step provides direct energy currency before further oxidation.
- Mnemonics for Cycle Intermediates -
Use "Citrate Is Krebs' Starting Substrate For Making Oxaloacetate" to recall the eight intermediates in order: citrate, isocitrate, α-ketoglutarate, succinyl-CoA, succinate, fumarate, malate, oxaloacetate. This mnemonic is invaluable for quick recall during a citric acid cycle quiz or tca cycle quiz and boosts retention under pressure.
- Regulation by Key Enzymes -
Citrate synthase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase are the primary control points, responding to ATP/ADP ratios, NADH levels, and availability of substrates (FDA Handbook on Metabolic Regulation). Allosteric activators like ADP enhance flux, while NADH and ATP act as feedback inhibitors to balance energy production with demand.