TCA
The Krebs Cycle
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Time limit: 50 minutes
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Multiple attempts are not allowed
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All questions must be answered to submit
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Question 1
What substance enters the Krebs Cycle?
Explanation
Acetyl-CoA is the molecule that enters the Krebs Cycle, derived from the breakdown of carbohydrates, fats, and proteins.
Question 2
Which of the following is a product of the Krebs Cycle?
Explanation
NADH is produced in the Krebs Cycle and serves as an important electron carrier for the subsequent stages of cellular respiration.
Question 3
What is the primary purpose of the Krebs Cycle in cellular respiration?
Explanation
The primary purpose of the Krebs Cycle is to generate ATP through the oxidation of acetyl-CoA, along with producing electron carriers (NADH and FADH2) that are used in the electron transport chain.
Question 4
Where does the Krebs Cycle take place in the cell?
Explanation
The Krebs Cycle occurs in the mitochondria of eukaryotic cells, where the conditions are suitable for aerobic respiration.
Question 5
Which of the following processes is directly linked to the Krebs Cycle?
Explanation
The electron transport chain is directly linked to the Krebs Cycle as it uses the NADH and FADH2 produced by the Krebs Cycle to generate ATP through oxidative phosphorylation.
Question 6
During cellular respiration, the Krebs Cycle plays a critical role in energy production. If a cell has an increased demand for ATP due to heightened metabolic activity, which aspect of the Krebs Cycle could be most significantly adjusted to meet this demand?
Explanation
Enhancing the activity of key dehydrogenase enzymes is correct, as they are crucial for the conversion of substrates into energy-rich molecules in the Krebs Cycle. The other options either do not directly relate to the Krebs Cycle or would not effectively increase ATP production.
Question 7
Imagine a specific genetic mutation occurs that reduces the efficiency of citrate synthase, the enzyme that catalyzes the first step of the Krebs Cycle. What effect would this mutation likely have on the overall metabolic pathways of the cell that uses the Krebs Cycle?
Explanation
The correct answer is that the mutation would lead to increased accumulation of acetyl-CoA and decreased ATP production, as a bottleneck in the first step would hinder the entire cycle. The other options are misconceptions because they misinterpret the consequences of an enzyme deficiency in the Krebs Cycle.
Question 8
[Case Scenario] A biologist is studying the Krebs Cycle to understand cellular respiration in eukaryotic cells. During her research, she notes that several enzymes play crucial roles in the cycle, such as citrate synthase and isocitrate dehydrogenase. She begins to analyze how the malfunction of any of these enzymes might affect the overall metabolic rate and energy production within the cell. Question: What might be the consequence of a deficiency in isocitrate dehydrogenase activity within the Krebs Cycle?
Explanation
The Krebs Cycle is critical for cellular respiration and energy production. Malfunctions in critical enzymes like isocitrate dehydrogenase can lead to metabolic disturbances, including substrate accumulation and energy deficits, which are pivotal for cellular functions.
Question 9
[Case Scenario] During a lab experiment, a student is tasked with measuring the effects of oxygen availability on the Krebs Cycle in muscle cells. He observes that under aerobic conditions, there are optimal levels of key metabolites such as NADH and FADH2 generated. However, when oxygen levels drop, he notices an alternative pathway is activated, leading to lactic acid production instead of full entry into the Krebs Cycle. Question: How does the change in oxygen availability impact the Krebs Cycle in muscle cells?
Explanation
The Krebs Cycle is linked to aerobic respiration, and lack of oxygen triggers anaerobic processes to ensure energy production continues, often resulting in lactic acid rather than complete oxidation of substrates.
Question 10
[Case Scenario] A group of researchers is examining how the Krebs Cycle contributes to the biomolecule synthesis in cancer cells. They find that certain cancer cells exhibit altered activity of specific enzymes such as aconitase, which can lead to changes in intermediate metabolite levels. Elevated levels of citrate in cancer cells were observed, leading the researchers to theorize a connection between altered Krebs Cycle activity and anabolic processes such as lipogenesis. Question: What is a likely consequence of elevated citrate levels in cancer cells related to the Krebs Cycle?
Explanation
Citrate plays a critical role extending beyond energy production, linking the Krebs Cycle to the synthesis of fatty acids in cancer cells. Its elevation is often a metabolic adaptative response that supports increased lipid production, highlighting the cycle's relevance in anabolic processes.