calculations
Theoretical yield of ATP, given 10 molecules of pyruvate?
150 ATP
pyruvate oxidation- 1 NADH
Krebs cycle- 3NADH, 1ATP & 1FADH2
ETC- 4 NADH*3 + 1FADH2 *2 +10* 1ATP= 150
Which of the following scenarios would most likely decrease the efficiency of the electron transport chain without completely halting ATP synthesis?
a) Complete inhibition of Complex I by rotenone
b) Partial uncoupling of oxidative phosphorylation by mild proton leak through the inner membrane
c) Overexpression of cytochrome c oxidase (Complex IV) in the mitochondria
d) Inhibition of ATP synthase by oligomycin
Answer: b) Partial uncoupling of oxidative phosphorylation by mild proton leak through the inner membrane
Which of the following is the first committed step of glycolysis?
a) Phosphorylation of glucose to glucose-6-phosphate by hexokinase
b) Phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate by phosphofructokinase-1 (PFK-1)
c) Conversion of glucose-6-phosphate to fructose-6-phosphate by phosphoglucose isomerase
d) Conversion of phosphoenolpyruvate (PEP) to pyruvate by pyruvate kinase
Answer: b) Phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate by phosphofructokinase-1 (PFK-1)
In the context of the Krebs cycle, which of the following best describes the regulation of isocitrate dehydrogenase in mammalian cells?
a) It is inhibited by ATP and activated by NADH
b) It is activated by ADP and Ca²⁺, and inhibited by ATP and NADH
c) It is phosphorylated and inactivated when acetyl-CoA levels are high
d) It is regulated primarily by substrate concentration and is insensitive to allosteric inhibitors
Answer: b) It is activated by ADP and Ca²⁺, and inhibited by ATP and NADH
Actual yield of 11 Phosphoenolpyruvate (PEP)
glycolysis- 11 pyruvate + 11 ATP
pyruvate oxidation- 11 acetyl coA + 11 nadh
krebs- 11 fadh2 + 33 nadh+11 atp
atp= 11+11= 22
nadh= 33+11= 44*2.5= 110
fadhs2= 11*1.5= 16.5
total= 22+110+16.5= 148.5 ATP
During ischemic conditions, the lack of oxygen can impair oxidative phosphorylation. Which specific aspect of the electron transport chain is most affected in such conditions?
a) The proton-pumping capacity of Complex II
b) The reduction of NAD⁺ by Complex I
c) The final transfer of electrons to oxygen at Complex IV
d) The oxidation of FADH₂ at Complex III
Answer: c) The final transfer of electrons to oxygen at Complex IV
Which enzyme of glycolysis is inhibited by high levels of ATP and citrate?
a) Phosphofructokinase-1 (PFK-1)
b) Pyruvate kinase
c) Hexokinase
d) Enolase
Answer: a) Phosphofructokinase-1 (PFK-1)
Which of the following enzymes is embedded in the inner mitochondrial membrane, unlike the others, which are found in the mitochondrial matrix?
a) α-Ketoglutarate dehydrogenase
b) Isocitrate dehydrogenase
c) Succinate dehydrogenase
d) Malate dehydrogenase
Answer: c) Succinate dehydrogenase
Actual yield on ATP using a molecule of Alanine and inhibiting malate dehydrogenase if oxidative phosphorylation is assumed.
When a molecule of alanine is converted to acetyl-CoA, it first undergoes transamination to form pyruvate, producing one NADH, which yields 2.5 ATP. In the Krebs cycle, acetyl-CoA generates two NADH (since malate dehydrogenase is inhibited), resulting in 5 ATP, one FADH₂, which yields 1.5 ATP, and one ATP directly from the cycle. Summing these yields, the total ATP produced from one molecule of alanine is 2.5 (from pyruvate) + 5 (from NADH in the Krebs cycle) + 1.5 (from FADH₂) + 1 (direct ATP), equaling 10 ATP overall.
If a mutation in Complex I disrupts its NADH dehydrogenase activity, which of the following effects would most likely be observed?
a) Increased proton pumping across Complex IV
b) Accumulation of NAD⁺ and decreased oxidative phosphorylation efficiency
c) Decreased FADH₂ oxidation and direct inhibition of Complex II
d) Increased cytochrome c oxidation due to electron leakage
Answer: b) Accumulation of NAD⁺ and decreased oxidative phosphorylation efficiency
During the "energy investment phase" of glycolysis, which of the following events occurs?
a) ATP is produced through substrate-level phosphorylation
b) NADH is produced by the oxidation of glyceraldehyde-3-phosphate
c) ATP is consumed to phosphorylate glucose and fructose-6-phosphate
d) Pyruvate is converted to lactate
Answer: c) ATP is consumed to phosphorylate glucose and fructose-6-phosphate
How does the regulation of citrate synthase ensure that the Krebs cycle responds to the cellular energy status?
a) Citrate synthase is activated by high levels of acetyl-CoA and inhibited by NADH
b) It is inhibited by ATP and NADH, and activated by ADP and Ca²⁺
c) Citrate synthase is competitively inhibited by citrate and activated by succinate
d) It is subject to feedback inhibition by oxaloacetate concentrations
Answer: b) It is inhibited by ATP and NADH, and activated by ADP and Ca²⁺
Using one molecule of G-3-P and inhibiting pyruvate dehydrogenase, how many actual ATP assuming electron carriers go through oxidative phosphorylation?
When **glyceraldehyde-3-phosphate (G3P)** is metabolized, it can directly enter glycolysis, yielding 1 NADH and 1 ATP per G3P molecule. If pyruvate dehydrogenase is inhibited, pyruvate cannot be converted to acetyl-CoA, so it will not enter the Krebs cycle. Therefore, G3P will be converted to lactate or used in other pathways, leading to no additional ATP production from the Krebs cycle or oxidative phosphorylation.
From the glycolysis of one molecule of G3P, you obtain 2 ATP (net yield from 1 G3P) and 1 NADH, which contributes 2.5 ATP. Thus, the total ATP yield from one G3P molecule, considering the inhibition of pyruvate dehydrogenase, is 2 ATP + 2.5 ATP, totaling **4.5 ATP**.
How does the ATP/ADP translocase protein function in relation to the electron transport chain?
a) It shuttles protons across the mitochondrial membrane to balance the proton gradient
b) It exchanges ATP from the mitochondrial matrix with ADP in the cytosol
c) It transfers electrons from NADH to Complex I
d) It serves as a carrier for Coenzyme Q
Answer: b) It exchanges ATP from the mitochondrial matrix with ADP in the cytosol
Which of the following statements is true regarding the regulation of hexokinase in glycolysis?
a) Hexokinase is activated by high concentrations of ATP
b) Hexokinase is inhibited by its product, glucose-6-phosphate
c) Hexokinase is inhibited by fructose-2,6-bisphosphate
d) Hexokinase is allosterically activated by citrate
Answer: b) Hexokinase is inhibited by its product, glucose-6-phosphate
Which of the following statements best explains why α-ketoglutarate dehydrogenase, rather than succinate dehydrogenase, is considered a key regulatory point in the Krebs cycle?
a) It is highly sensitive to feedback inhibition by ATP, NADH, and succinyl-CoA
b) Succinate dehydrogenase is membrane-bound and less responsive to changes in substrate availability
c) α-Ketoglutarate dehydrogenase is allosterically activated by ADP and AMP, whereas succinate dehydrogenase is not
d) The conversion of α-ketoglutarate to succinyl-CoA is rate-limiting due to the irreversible release of CO₂
Answer: a) It is highly sensitive to feedback inhibition by ATP, NADH, and succinyl-CoA
12 molecules of Fructose-6-P enter cellular respiration stages with succinate dehydrogenase inhibited. Assuming oxidative phosphorylation, what is the ATP yield?
When **12 fructose-6-phosphate (F6P)** molecules are metabolized, they enter glycolysis, yielding a total of 24 ATP and 24 NADH (since each F6P produces 2 ATP and 2 NADH). The 24 NADH yield an additional 60 ATP (24 NADH × 2.5 ATP each). The pyruvate generated from glycolysis is converted to acetyl-CoA, producing 12 NADH, which contributes another 30 ATP (12 NADH × 2.5 ATP each). In the Krebs cycle, with succinate dehydrogenase inhibited, each of the 12 acetyl-CoA molecules produces 2 NADH (yielding 30 ATP) and 12 ATP directly.
Thus, the total ATP yield from 12 F6P is calculated as follows: 24 ATP from glycolysis, 60 ATP from NADH during glycolysis, 30 ATP from NADH during pyruvate conversion, and 30 ATP plus 12 ATP from the Krebs cycle. This results in a total of **156 ATP**.
Which statement accurately describes the coupling between electron transport and ATP synthesis in oxidative phosphorylation?
a) ATP synthesis occurs spontaneously without requiring a proton gradient
b) ATP synthesis is directly driven by electron movement between complexes
c) ATP synthesis is coupled to the flow of protons back into the matrix through ATP synthase
d) ATP synthesis can occur in the absence of oxygen due to the electron transport chain
Answer: c) ATP synthesis is coupled to the flow of protons back into the matrix through ATP synthase
In the context of glycolysis, what is the primary reason that the conversion of phosphoenolpyruvate (PEP) to pyruvate by pyruvate kinase is irreversible?
a) The reaction involves the hydrolysis of ATP to ADP, driving it forward
b) Pyruvate undergoes rapid conversion to lactate or acetyl-CoA, depleting pyruvate concentration
c) PEP has a very high phosphoryl transfer potential, making the reaction highly exergonic
d) The reaction is tightly regulated by NADH and NAD⁺ concentrations
Answer: c) PEP has a very high phosphoryl transfer potential, making the reaction highly exergonic
Which of the following enzymes in the Krebs cycle uses a substrate-level phosphorylation mechanism to generate GTP or ATP?
a) Succinate dehydrogenase
b) α-Ketoglutarate dehydrogenase
c) Succinyl-CoA synthetase
d) Malate dehydrogenase
Answer: c) Succinyl-CoA synthetase