Biochemistry Quiz: Fatty Acid Synthesis And Regulation

What this quiz covers

This quiz focuses on Fatty Acid Synthesis And Regulation, giving you a quick way to practice the rules, question types, and explanations that matter most for Biochemistry.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. (^{14}\text{C})-labeled acetyl-CoA, which is directly condensed onto the growing acyl chain by fatty acid synthase.
2. (^{14}\text{C})-labeled malonyl-CoA, which is synthesized from acetyl-CoA and provides the activated two-carbon unit for each condensation step. (correct answer)
3. (^{14}\text{C})-labeled pyruvate, which is directly used by the fatty acid synthase complex as a carbon source.
4. (^{14}\text{C})-labeled acetoacetyl-ACP, which is formed from two acetyl-CoA molecules and serves as the universal elongating group.

Explanation: While acetyl-CoA primes the synthesis (providing C15 and C16 of palmitate), all subsequent two-carbon additions use malonyl-CoA as the substrate. The (^{14}\text{C})-glucose is metabolized to (^{14}\text{C})-pyruvate, then to mitochondrial (^{14}\text{C})-acetyl-CoA. This is transported to the cytosol (via citrate) and then carboxylated by ACC to form (^{14}\text{C})-malonyl-CoA, the immediate donor for elongation by fatty acid synthase.

Question 2

1. It is released as (\text{CO}_2), and the resulting decarboxylation drives the condensation reaction forward. (correct answer)
2. It is reduced by NADPH and incorporated into the growing fatty acyl chain as a methyl group.
3. It becomes the carbonyl carbon of the newly elongated β-ketoacyl-ACP intermediate.
4. It remains attached to the coenzyme A moiety, which is released after the malonyl group is transferred to ACP.

Explanation: Malonyl-CoA is an activated two-carbon donor. Its third carbon is the carboxyl group that was added by acetyl-CoA carboxylase. During the condensation step on the FAS complex, the malonyl group (attached to ACP) attacks the growing acyl chain. This reaction is coupled to a decarboxylation, where this third carbon is released as (\text{CO}_2). The release of (\text{CO}_2) makes the reaction highly exergonic and essentially irreversible, driving the entire synthetic process.

Question 3

1. It directly inhibits carnitine acyltransferase I, preventing mitochondrial fatty acid import and creating a futile cycle with beta-oxidation.
2. It activates acetyl-CoA carboxylase, committing acetyl-CoA to fatty acid synthesis, while its cleavage by ATP-citrate lyase provides the substrate for this reaction. (correct answer)
3. It activates fatty acid synthase, increasing the rate of palmitate elongation, thereby pulling the acetyl-CoA carboxylase reaction forward to generate more substrate.
4. It is cleaved to produce acetyl-CoA for synthesis and oxaloacetate, which is immediately converted to malate to generate all the NADPH required for synthesis.

Explanation: Elevated cytosolic citrate indicates an energy-rich state and an abundance of acetyl-CoA in the mitochondria. Citrate is transported to the cytosol where it is cleaved by ATP-citrate lyase into acetyl-CoA (the substrate for synthesis) and oxaloacetate. Simultaneously, citrate acts as a potent feed-forward allosteric activator of acetyl-CoA carboxylase (ACC), the rate-limiting enzyme, thus coupling substrate availability with enzymatic commitment.

Question 4

1. The lack of malic enzyme activity causes malate to accumulate, which allosterically inhibits the transport of citrate from the mitochondria.
2. The conversion of malate to pyruvate is a required step for regenerating the oxaloacetate needed for the citrate shuttle to function continuously.
3. The reaction catalyzed by malic enzyme is a significant source of the cytosolic NADPH required for the reductive reactions of fatty acid synthesis. (correct answer)
4. The pyruvate produced by malic enzyme is the primary source of the acetyl-CoA used for the initial priming step of fatty acid synthesis.

Explanation: Fatty acid synthesis is a reductive process that requires a large amount of NADPH. While the pentose phosphate pathway is the primary source, the cytosolic enzyme malic enzyme also contributes significantly. It catalyzes the oxidative decarboxylation of malate to pyruvate, converting NADP⁺ to NADPH. A defect in this enzyme would reduce the total available pool of cytosolic NADPH, thereby limiting the rate at which fatty acid synthase can perform its reductive steps, even if substrates and enzymes are otherwise plentiful.

Question 5

1. Seven molecules of G6P must enter the oxidative phase of the pentose phosphate pathway, as each pass generates two molecules of NADPH. (correct answer)
2. Fourteen molecules of G6P must be fully catabolized by the pentose phosphate pathway, with each G6P yielding one NADPH for fatty acid synthesis.
3. Four molecules of G6P must enter the pathway, with subsequent recycling of intermediates to generate the remaining required reducing equivalents.
4. Eight molecules of G6P are required, stoichiometrically matching the eight molecules of acetyl-CoA that are incorporated into the final palmitate.

Explanation: The synthesis of one molecule of palmitate requires 14 NADPH. The oxidative phase of the pentose phosphate pathway generates two molecules of NADPH for every one molecule of glucose-6-phosphate that is converted to ribulose-5-phosphate. Therefore, to produce 14 NADPH, 7 molecules of glucose-6-phosphate are required (14 NADPH / 2 NADPH per G6P = 7 G6P).

Question 6

1. Stearate is directly synthesized by FAS if the cell is provided with a different primer molecule instead of acetyl-CoA.
2. They are produced by separate elongase enzyme systems in the endoplasmic reticulum which add two-carbon units to palmitoyl-CoA. (correct answer)
3. FAS continues the elongation cycle one additional time using another malonyl-CoA before releasing the 18-carbon product.
4. They are obtained exclusively from the diet, as mammalian cells lack the enzymes to extend fatty acids beyond 16 carbons.

Explanation: De novo synthesis in the cytosol yields palmitate. To create longer-chain fatty acids like stearate, cells utilize separate enzyme systems called elongases. These enzymes are primarily located in the membrane of the endoplasmic reticulum. They use malonyl-CoA as the two-carbon donor to extend palmitoyl-CoA (or other fatty acyl-CoAs), effectively adding two carbons at a time in a process mechanistically similar but catalyzed by different proteins than FAS.

Question 7

1. Palmitoyl-CoA, which provides feedback inhibition on the carnitine acyltransferase I (CAT I) transporter.
2. Malonyl-CoA, which allosterically inhibits carnitine acyltransferase I (CAT I), blocking fatty acyl-CoA entry into mitochondria. (correct answer)
3. Cytosolic acetyl-CoA, which competitively inhibits the active site of carnitine acyltransferase I (CAT I).
4. Insulin, which directly signals the mitochondrial transporters to halt import of fatty acyl-CoAs during the fed state.

Explanation: When fatty acid synthesis is active, acetyl-CoA carboxylase produces high levels of malonyl-CoA. Malonyl-CoA is a potent allosteric inhibitor of carnitine acyltransferase I (CAT I), the enzyme that controls the entry of long-chain fatty acyl-CoAs into the mitochondrial matrix for β-oxidation. This ensures that synthesis and degradation do not occur simultaneously.

Question 8

1. The cleavage of cytosolic citrate to acetyl-CoA and oxaloacetate by ATP-citrate lyase.
2. The conversion of malate to pyruvate by malic enzyme to generate cytosolic NADPH.
3. The formation of malonyl-CoA from acetyl-CoA and bicarbonate by acetyl-CoA carboxylase. (correct answer)
4. The reduction of ketoacyl groups to hydroxyl groups by fatty acid synthase during elongation.

Explanation: Biotin is an essential coenzyme for carboxylase enzymes, where it functions as a carrier of activated CO₂. Acetyl-CoA carboxylase (ACC), which catalyzes the carboxylation of acetyl-CoA to form malonyl-CoA, is a biotin-dependent enzyme. A deficiency in biotin would cripple this rate-limiting step, thereby halting de novo fatty acid synthesis.

Question 9

1. Fatty acid synthesis would be constitutively active, as ACC would be permanently locked in a dephosphorylated, high-activity conformation.
2. Fatty acid synthesis would become insensitive to inhibition by glucagon and epinephrine, but still responsive to cellular AMP levels via other mechanisms.
3. Fatty acid synthesis would be inhibited even in high-energy states, as the mutation would prevent activating phosphorylation by other kinases.
4. Fatty acid synthesis would fail to be suppressed during low-energy conditions, as AMPK could no longer phosphorylate and inactivate the enzyme. (correct answer)

Explanation: AMPK phosphorylates a specific serine residue on ACC to inactivate it in response to low energy (high AMP/ATP ratio). Replacing this serine with alanine, which cannot be phosphorylated, removes this crucial inhibitory control point. Therefore, even when AMPK is activated by low energy, it cannot shut off ACC, and the energy-consuming process of fatty acid synthesis would inappropriately continue.

Question 10

1. The ACC reaction is highly reversible, allowing for rapid flux control in either direction depending on metabolic needs of the cell.
2. The product, malonyl-CoA, has no other major metabolic fate besides fatty acid synthesis, so regulating its production prevents wasteful synthesis of a dedicated intermediate. (correct answer)
3. ACC is the only enzyme in the pathway that uses the cofactor biotin, making it a unique target for vitamin-level regulation.
4. Regulating ACC prevents the consumption of acetyl-CoA, which is more critically needed to fuel the citric acid cycle for ATP production.

Explanation: Metabolic pathways are most efficiently regulated at their first committed step. This is the first irreversible reaction that is unique to the pathway. Once malonyl-CoA is formed from acetyl-CoA, it is essentially committed to entering the fatty acid synthesis pathway. By regulating ACC, the cell avoids expending ATP and carbon to create an intermediate that has no other significant use.

Question 11

1. High glucagon activates PKA, which phosphorylates and inactivates ACC, while low citrate levels remove allosteric activation.
2. High insulin activates a phosphatase, which dephosphorylates and activates ACC, an effect enhanced by high citrate levels. (correct answer)
3. Low insulin fails to suppress AMPK, which phosphorylates and inhibits ACC, overriding any activation by citrate.
4. High epinephrine from the meal stress activates PKA, which phosphorylates ACC, while high palmitoyl-CoA provides feedback inhibition.

Explanation: A high-carbohydrate meal raises blood glucose, leading to insulin secretion. Insulin signaling activates protein phosphatases (like PP2A) that dephosphorylate and activate ACC. Concurrently, the high influx of carbohydrates into glycolysis and the TCA cycle leads to an accumulation of mitochondrial citrate, which is transported to the cytosol. This elevated cytosolic citrate allosterically activates ACC, working in concert with the covalent dephosphorylation to strongly promote fatty acid synthesis.

Question 12

1. An accumulation of mitochondrial acetyl-CoA and a significant decrease in fatty acid synthesis. (correct answer)
2. An increase in cytosolic acetyl-CoA due to compensatory pathways and an increase in fatty acid synthesis.
3. A depletion of mitochondrial citrate due to its rapid export and subsequent cleavage in the cytosol.
4. A decrease in β-oxidation rates because the lack of cytosolic acetyl-CoA inhibits the carnitine shuttle.

Explanation: ATP-citrate lyase is the enzyme responsible for cleaving citrate in the cytosol to produce acetyl-CoA for fatty acid synthesis. Under high-glucose conditions, pyruvate enters the mitochondria and is converted to acetyl-CoA, which then forms citrate. Citrate is exported to the cytosol. By inhibiting ATP-citrate lyase, the drug prevents the generation of cytosolic acetyl-CoA, thus halting fatty acid synthesis. This causes citrate and its precursor, acetyl-CoA, to accumulate in the mitochondria.

Question 13

1. Allosteric inhibition of fatty acid synthase by high concentrations of AMP.
2. Activation of AMP-activated protein kinase (AMPK), which phosphorylates and inactivates acetyl-CoA carboxylase (ACC). (correct answer)
3. Depletion of acetyl-CoA as it is preferentially shunted into the citric acid cycle, starving the synthesis pathway of substrate.
4. Hormonal signals, such as epinephrine, which cause the dephosphorylation and inactivation of ACC.

Explanation: A high AMP/ATP ratio is a key indicator of low cellular energy. This ratio allosterically activates AMP-activated protein kinase (AMPK). Activated AMPK acts as a master metabolic regulator, phosphorylating and inactivating key enzymes in ATP-consuming anabolic pathways. A primary target is acetyl-CoA carboxylase (ACC), which is inhibited upon phosphorylation, thereby shutting down the energy-expensive process of fatty acid synthesis to conserve ATP.

Question 14

1. Only at carbon 1 (the carboxyl carbon) of the final palmitate molecule.
2. Exclusively at carbon 15 of the final palmitate molecule.
3. At all the even-numbered carbons of the palmitate molecule.
4. At all the odd-numbered carbons except for carbon 15. (correct answer)

Explanation: When you encounter fatty acid synthesis labeling questions, focus on tracking which carbons from the starting materials end up where in the final product and what happens during the decarboxylation step. In fatty acid synthesis, palmitate is built by adding two-carbon units from malonyl-CoA to a growing chain that starts with acetyl-CoA. The key mechanism is that malonyl-CoA undergoes decarboxylation during each addition cycle - its carboxyl group (the unlabeled carbon) is released as CO₂, while the remaining two-carbon unit (including the labeled carbonyl carbon) gets incorporated into the growing fatty acid chain. Since the $^{14}C$ label is on the carbonyl carbon of malonyl-CoA, this labeled carbon becomes incorporated at specific positions. The acetyl-CoA starter unit contributes carbons 15 and 16 (the methyl end), so carbon 15 remains unlabeled. Each malonyl-CoA addition contributes two carbons to the growing chain, with the labeled carbonyl carbon ending up at odd-numbered positions 1, 3, 5, 7, 9, 11, and 13. Therefore, the label appears at all odd-numbered carbons except carbon 15, making D correct. Option A is wrong because the label appears at multiple positions, not just carbon 1. Option B incorrectly places the label at carbon 15, which comes from unlabeled acetyl-CoA. Option C mistakenly suggests even-numbered carbons are labeled, but these positions receive the methyl carbons from malonyl-CoA, not the labeled carbonyl carbons. Study tip: Remember that in fatty acid synthesis, decarboxylation removes the carboxyl carbon from malonyl-CoA, so track where the carbonyl carbon ends up, not where the whole malonyl-CoA molecule goes.

Question 15

1. Short-term: feedback inhibition by palmitoyl-CoA is removed. Long-term: glucagon signaling decreases the transcription of the ACC gene.
2. Short-term: covalent activation of FAS by phosphorylation. Long-term: increased expression of carnitine acyltransferase I.
3. Short-term: gene expression for ACC and FAS is rapidly induced. Long-term: ACC is persistently dephosphorylated and thus activated.
4. Short-term: allosteric activation of ACC by citrate increases. Long-term: insulin-mediated signaling upregulates the transcription of ACC and FAS genes. (correct answer)

Explanation: When analyzing metabolic shifts between different diets, you need to distinguish between rapid regulatory mechanisms (allosteric control and covalent modification) and slower transcriptional changes that occur over days. The switch from high-fat to high-carbohydrate intake creates immediate metabolic changes. Increased glucose metabolism produces more citrate through the citric acid cycle. Citrate serves as a key allosteric activator of acetyl-CoA carboxylase (ACC), the rate-limiting enzyme in fatty acid synthesis. This represents the primary short-term mechanism for increasing lipogenesis within minutes to hours. Over days, the sustained high-carbohydrate, low-fat environment triggers insulin signaling pathways that upregulate transcription of lipogenic genes, including ACC and fatty acid synthase (FAS). Option A incorrectly suggests glucagon decreases ACC transcription - actually, insulin (not glucagon) drives lipogenic gene expression, and glucagon would have the opposite effect. Option B wrongly states that FAS is activated by phosphorylation; FAS activity is primarily regulated at the transcriptional level, not through covalent modification. Option C reverses the timeframes - gene expression changes occur over days, not rapidly, while ACC dephosphorylation (though important) isn't the primary long-term mechanism compared to increased gene transcription. Remember that metabolic regulation follows a hierarchy: allosteric control provides immediate responses (seconds to minutes), covalent modification offers intermediate control (minutes to hours), and transcriptional regulation creates sustained changes (hours to days). Questions about dietary transitions often test your understanding of these different temporal mechanisms.

Question 16

1. Insulin promotes transcription of lipogenic enzymes, while glucose inhibits AMP-activated protein kinase that normally suppresses acetyl-CoA carboxylase activity during fasting
2. Insulin increases fatty acid synthase expression, while glucose provides NADPH through the pentose phosphate pathway that is essential for reductive fatty acid synthesis
3. Insulin activates acetyl-CoA carboxylase and fatty acid synthase through phosphorylation, while glucose provides ATP for the energy-requiring steps of fatty acid synthesis
4. Insulin activates acetyl-CoA carboxylase through dephosphorylation, while glucose provides citrate via glycolysis to generate cytosolic acetyl-CoA through ATP citrate lyase (correct answer)

Explanation: When you encounter questions about metabolic regulation, focus on how hormones and substrates work together at different levels - transcriptional, post-translational, and substrate availability. The key insight here is that fatty acid synthesis requires both regulatory activation and substrate supply. Insulin provides the hormonal signal by dephosphorylating (activating) acetyl-CoA carboxylase, the rate-limiting enzyme. However, activation alone isn't sufficient - you also need cytosolic acetyl-CoA, the building block for fatty acid synthesis. Glucose provides this through glycolysis: glucose is converted to pyruvate, which enters mitochondria and forms acetyl-CoA. This acetyl-CoA condenses with oxaloacetate to form citrate, which exits the mitochondria and is cleaved by ATP citrate lyase to regenerate cytosolic acetyl-CoA for fatty acid synthesis. Option A incorrectly suggests insulin works transcriptionally here and misrepresents glucose's role with AMPK. While glucose can affect AMPK, the primary mechanism is substrate provision. Option B confuses fatty acid synthase regulation with the more critical acetyl-CoA carboxylase step, and while glucose can contribute to NADPH via the pentose phosphate pathway, this isn't the limiting factor in this scenario. Option C incorrectly states that insulin activates acetyl-CoA carboxylase through phosphorylation - it's actually dephosphorylation that activates this enzyme. Remember: in fatty acid synthesis questions, always consider both the regulatory mechanisms (insulin's dephosphorylation of ACC) and substrate requirements (cytosolic acetyl-CoA from the citrate-malate shuttle). Both must be present for maximal activity.

Question 17

1. Heart muscle cells maintain chronically elevated AMPK activity due to high energy demands, leading to persistent inhibition of acetyl-CoA carboxylase
2. Heart muscle cells lack sufficient ATP citrate lyase activity to generate adequate cytosolic acetyl-CoA substrate for fatty acid synthesis pathways
3. Heart muscle cells have higher malonyl-CoA decarboxylase activity, which depletes malonyl-CoA pools needed for fatty acid chain elongation reactions
4. Heart muscle cells have significantly lower fatty acid synthase expression compared to liver cells, reflecting their primary role in fatty acid oxidation rather than synthesis (correct answer)

Explanation: When analyzing tissue-specific differences in metabolic pathways, consider that different tissues are specialized for distinct metabolic roles. Liver is the body's primary biosynthetic organ, while heart muscle is optimized for energy production through oxidation. The key insight here is that both cell types showed similar acetyl-CoA carboxylase activity, yet fatty acid synthesis rates differed dramatically. This tells you the bottleneck isn't in the rate-limiting enzyme that produces malonyl-CoA, but must be elsewhere in the pathway. Answer D correctly identifies that heart muscle cells have much lower fatty acid synthase expression. Heart muscle is metabolically specialized for fatty acid oxidation to meet its enormous energy demands, not for lipogenesis. The liver, conversely, is a major site of fatty acid synthesis and lipid storage, requiring high fatty acid synthase levels. Answer A is incorrect because while AMPK does inhibit acetyl-CoA carboxylase, the question states both tissues show similar carboxylase activity, ruling out this explanation. Answer B misses the mark because ATP citrate lyase deficiency would also affect acetyl-CoA carboxylase activity, contradicting the given data. Answer C about malonyl-CoA decarboxylase is wrong because this enzyme's primary role is removing the inhibitory effect of malonyl-CoA on fatty acid oxidation, not depleting substrate for synthesis. Remember that tissue-specific metabolism questions often test whether you understand that enzyme expression patterns match tissue function. Always consider what each tissue's primary metabolic role is—synthesis versus oxidation, storage versus energy production.

Question 18

1. ACC inhibition activates AMP-activated protein kinase through feedback mechanisms, which then stimulates both fatty acid oxidation and gluconeogenic enzyme expression
2. Inhibition of ACC redirects acetyl-CoA toward the citric acid cycle, generating more NADH and ATP that drives gluconeogenesis and fatty acid oxidation simultaneously
3. Reduced ACC activity decreases malonyl-CoA production, which relieves inhibition of CPT1, allowing increased fatty acid oxidation that provides acetyl-CoA for gluconeogenesis (correct answer)
4. Decreased fatty acid synthesis reduces cellular lipid content, which enhances membrane permeability to fatty acids and glucose precursors, accelerating both oxidation and gluconeogenesis

Explanation: When you encounter questions about metabolic enzyme inhibition, focus on the direct product effects and their downstream regulatory consequences. This question tests your understanding of how fatty acid synthesis and oxidation are reciprocally regulated. Acetyl-CoA carboxylase (ACC) catalyzes the rate-limiting step of fatty acid synthesis, converting acetyl-CoA to malonyl-CoA. The key insight is that malonyl-CoA serves dual roles: it's both a substrate for fatty acid synthesis AND a potent inhibitor of CPT1 (carnitine palmitoyltransferase I), the rate-limiting enzyme for fatty acid oxidation. When ACC is inhibited by 80%, malonyl-CoA levels plummet, which directly relieves CPT1 inhibition. This allows fatty acids to enter mitochondria for β-oxidation, producing acetyl-CoA that can be converted to glucose via gluconeogenesis. Answer C correctly identifies this mechanism. Answer A incorrectly suggests AMPK activation causes these effects. While AMPK does regulate these pathways, the question describes direct effects of ACC inhibition, not AMPK-mediated responses. Answer B misunderstands the metabolic flow - reduced ACC activity doesn't redirect acetyl-CoA to the citric acid cycle; instead, it prevents acetyl-CoA from becoming malonyl-CoA. Answer D proposes an implausible membrane permeability mechanism that doesn't align with established biochemical regulation. Remember this regulatory principle: malonyl-CoA acts like a metabolic switch, promoting fatty acid synthesis while blocking fatty acid oxidation. When you inhibit its production, you flip the switch toward oxidation and away from synthesis.

Question 19

1. Compound X activates AMP-activated protein kinase (AMPK), leading to phosphorylation and inactivation of ACC, while okadaic acid prevents dephosphorylation and reactivation of ACC (correct answer)
2. Compound X activates AMP-activated protein kinase (AMPK), leading to phosphorylation and inactivation of ACC, while okadaic acid prevents this phosphorylation by inhibiting AMPK
3. Compound X inhibits citrate lyase activity directly, while okadaic acid restores citrate lyase function through an unknown phosphatase-dependent mechanism
4. Compound X depletes cellular malonyl-CoA pools through enhanced oxidation, while okadaic acid prevents this depletion by inhibiting malonyl-CoA degrading enzymes

Explanation: The key observation is that okadaic acid (protein phosphatase inhibitor) rescues fatty acid synthesis. This suggests that compound X works through a phosphorylation mechanism that inactivates ACC, and okadaic acid prevents the dephosphorylation that would normally reactivate ACC. AMPK phosphorylates and inactivates ACC. Choice B is incorrect because okadaic acid inhibits phosphatases, not kinases like AMPK. Choice C is incorrect because the problem states citrate levels are unchanged. Choice D is incorrect because it doesn't explain why a phosphatase inhibitor would rescue synthesis.

Question 20

1. ATP citrate lyase deficiency, preventing the conversion of citrate to acetyl-CoA in the cytosol for fatty acid synthesis (correct answer)
2. Pyruvate dehydrogenase deficiency, preventing the formation of acetyl-CoA from glucose-derived pyruvate in the mitochondria
3. Fatty acid synthase deficiency, preventing the elongation of the fatty acid chain from malonyl-CoA and acetyl-CoA
4. Malic enzyme deficiency, preventing the regeneration of NADPH required for fatty acid synthesis reactions

Explanation: ATP citrate lyase is essential for generating cytosolic acetyl-CoA from citrate for fatty acid synthesis. Without this enzyme, citrate accumulates (as observed) but cannot be converted to acetyl-CoA, leading to low ACC activity due to lack of substrate. Choice B is incorrect because pyruvate dehydrogenase operates in mitochondria and wouldn't directly affect cytosolic acetyl-CoA. Choice C is incorrect because fatty acid synthase deficiency would not affect ACC activity. Choice D is incorrect because malic enzyme deficiency would affect NADPH levels but not directly impact ACC activity, and the problem doesn't mention NADPH depletion.