Biochemistry - Glycolysis & Gluconeogensis Questions

1.

State the stoichiometry of the glycolytic pathway, in relation to both ATP and NADH production. Describe the appropriate reactions in your answer.
2.

Describe the fates of pyruvate in both aerobic and anaerobic tissues.
3.

Explain the steps in the gluconeogenesis pathway which are not the reverse of reactions of the glycolysis pathway.
4.

Which statement about glycolysis is correct
- A.
  
  The reaction pathway liberates 1400 kJ/mol of energy
- B.
  
  The pathway involves 10 reactions
- C.
  
  5 of the reactions in glycolysis are essentially irreversible
- D.
  
  The coenzyme NADPH is required in the pathway
- E.
  
  Involves the splitting of a 6 carbon compound into three 2 carbon compounds
Correct Answer
B. The pathway involves 10 reactions

Explanation
Glycolysis is a metabolic pathway that involves the breakdown of glucose into pyruvate. It is a series of 10 reactions that occur in the cytoplasm of cells. Each reaction is catalyzed by a specific enzyme, and the overall process results in the production of ATP and NADH. Therefore, the statement that "The pathway involves 10 reactions" is correct.

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5.

In glycolysis, most reactions have G values around zero except:
- A.
  
  Reactions 1, 3, 10
- B.
  
  Reactions 2, 4, 5
- C.
  
  Reactions 7 and 8
- D.
  
  Reactions 9 and 10
- E.
  
  Reaction 8 and 10
Correct Answer
A. Reactions 1, 3, 10
6.

The catabolism of 4 mol of glucose into 8 mol of pyruvate via glycolysis yields:
- A.
  
  1 mol of ATP and 4 mol of NADH
- B.
  
  2 mol of ATP and 1 mol of NADH
- C.
  
  8 mol of ATP and 8 mol of NADH
- D.
  
  32 mol of ATP and 2 mol of NADH
- E.
  
  None of the above
Correct Answer
C. 8 mol of ATP and 8 mol of NADH

Explanation
During the catabolism of 4 mol of glucose into 8 mol of pyruvate via glycolysis, a net of 8 mol of ATP is produced through substrate-level phosphorylation. Additionally, 8 mol of NADH is generated through the reduction of NAD+ to NADH. This occurs through the oxidation of glucose and subsequent formation of pyruvate. Therefore, the correct answer is 8 mol of ATP and 8 mol of NADH.

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7.

Following glycolysis, which of these molecules is NOT a possible fate of pyruvate catabolism?
- A.
  
  Glycogen
- B.
  
  CO2
- C.
  
  Ethanol
- D.
  
  Lactate
- E.
  
  Acetyl CoA
Correct Answer
A. Glycogen

Explanation
Glycogen is not a possible fate of pyruvate catabolism because pyruvate cannot be directly converted into glycogen. Instead, pyruvate can be converted into CO2, ethanol, lactate, or Acetyl CoA through various metabolic pathways. Glycogen is a storage form of glucose and is synthesized from glucose molecules, not from pyruvate.

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8.

In glycolysis, the reaction(s) that produce(s) NADH is?
- A.
  
  Reaction 5
- B.
  
  Reaction 6
- C.
  
  Reactions 5 & 6
- D.
  
  Reaction 9
- E.
  
  Reaction 7
Correct Answer
B. Reaction 6

Explanation
In glycolysis, reaction 6 produces NADH. This reaction involves the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, with the reduction of NAD+ to NADH. This reaction is important because it generates NADH, which can then be used in the later steps of glycolysis and in other metabolic pathways.

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9.

In glycolysis, the two priming reactions (requiring ATP) are?
- A.
  
  1 & 3
- B.
  
  7 & 10
- C.
  
  6 & 4
- D.
  
  7 & 9
- E.
  
  3 & 7
Correct Answer
A. 1 & 3

Explanation
The two priming reactions in glycolysis that require ATP are reactions 1 and 3. In reaction 1, glucose is converted to glucose-6-phosphate with the help of ATP. In reaction 3, fructose-6-phosphate is converted to fructose-1,6-bisphosphate also with the help of ATP. These priming reactions are essential for the subsequent steps of glycolysis to occur, as they provide the necessary energy to drive the process forward.

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10.

In comparison with the resting state, actively contracting human muscle tissue has a
- A.
  
  Higher concentrations of ATP
- B.
  
  Higher rate of lactate formation
- C.
  
  Lower consumption of glucose
- D.
  
  Lower rate of consumption of oxygen
- E.
  
  Lower ratio of NADH to NAD+
Correct Answer
B. Higher rate of lactate formation

Explanation
During muscle contraction, the demand for energy increases, leading to higher concentrations of ATP. To meet this demand, the breakdown of glucose is accelerated, resulting in a higher rate of lactate formation. This occurs when the breakdown of glucose proceeds faster than the rate at which it can be completely oxidized to produce ATP. Therefore, the higher rate of lactate formation is a result of the increased energy requirements during muscle contraction.

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11.

Which statement about the energy production and usage in glycolysis and gluconeogenesis is correct?
- A.
  
  Glycolysis produces 2 ATP; gluconeogenesis requires 2 ATP
- B.
  
  Glycolysis produces 32 ATP; gluconeogenesis produces 2 ATP
- C.
  
  Glycolysis requires a net input of 2 ATP to run the final reaction (step 10); gluconeogenesis requires the net input of 6 ATP
- D.
  
  Glycolysis uses 2 ATP but produces 4 ATP. Gluconeogenesis requires 4 ATP and 2 GTP
- E.
  
  All enzymes in glycolysis and gluconeogenesis require energy in the form of ATP
Correct Answer
D. Glycolysis uses 2 ATP but produces 4 ATP. Gluconeogenesis requires 4 ATP and 2 GTP

Explanation
Glycolysis is a metabolic pathway that breaks down glucose to produce energy in the form of ATP. It uses 2 ATP molecules as an initial investment but ultimately produces 4 ATP molecules. This is due to the production of 4 ATP molecules through substrate-level phosphorylation. On the other hand, gluconeogenesis is a process that synthesizes glucose from non-carbohydrate sources. It requires 4 ATP and 2 GTP molecules for the conversion of pyruvate to glucose. Therefore, the statement "Glycolysis uses 2 ATP but produces 4 ATP. Gluconeogenesis requires 4 ATP and 2 GTP" is correct as it accurately describes the energy production and usage in both pathways.

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12.

The irreversible reactions of glycolysis are bypassed in gluconeogenesis using the following enzymes:
- A.
  
  Oxaloacetase, PFK-1, glycogen phosphorylase, debranching enzyme
- B.
  
  Phosphoglucomutase, branching enzyme, glycogen synthase
- C.
  
  PFK-1, Hexokinase, Aldolase
- D.
  
  Glucose 6-phosphatase; fructose 1,6 bisphosphatase; Pyruvate carboxylase; PEP carboxykinase
- E.
  
  NADH, FADH2, glucose, glycogen
Correct Answer
D. Glucose 6-pHospHatase; fructose 1,6 bispHospHatase; Pyruvate carboxylase; PEP carboxykinase

Explanation
Gluconeogenesis is the process by which glucose is synthesized from non-carbohydrate precursors. It is essentially the reverse of glycolysis, with a few key differences. The irreversible reactions of glycolysis are bypassed in gluconeogenesis by using specific enzymes. Glucose 6-phosphatase is responsible for converting glucose 6-phosphate to glucose, allowing glucose to be released into the bloodstream. Fructose 1,6 bisphosphatase catalyzes the hydrolysis of fructose 1,6 bisphosphate to fructose 6-phosphate, an important step in reversing the committed step of glycolysis. Pyruvate carboxylase and PEP carboxykinase are involved in converting pyruvate to phosphoenolpyruvate (PEP), another key step in gluconeogenesis. These enzymes are necessary for the synthesis of glucose from non-carbohydrate sources.

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13.

Which enzyme does NOT catalyse an irreversible reaction in either glycolysis or gluconeogenesis?
- A.
  
  Hexokinase
- B.
  
  Glucose 6-phosphatase
- C.
  
  Pyruvate kinase
- D.
  
  Phosphofructokinase-1
- E.
  
  Enolase
Correct Answer
E. Enolase

Explanation
Enolase is the correct answer because it catalyzes a reversible reaction in both glycolysis and gluconeogenesis. It converts 2-phosphoglycerate to phosphoenolpyruvate in glycolysis and the reverse reaction in gluconeogenesis. The other enzymes listed in the options catalyze irreversible reactions in either glycolysis or gluconeogenesis. Hexokinase phosphorylates glucose to glucose 6-phosphate, glucose 6-phosphatase dephosphorylates glucose 6-phosphate to glucose, pyruvate kinase converts phosphoenolpyruvate to pyruvate, and phosphofructokinase-1 phosphorylates fructose 6-phosphate to fructose 1,6-bisphosphate.

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Biochemistry - Glycolysis & Gluconeogensis Questions

State the stoichiometry of the glycolytic pathway, in relation to both ATP and NADH production. Describe the appropriate reactions in your answer.

Describe the fates of pyruvate in both aerobic and anaerobic tissues.

Explain the steps in the gluconeogenesis pathway which are not the reverse of reactions of the glycolysis pathway.

Which statement about glycolysis is correct

In glycolysis, most reactions have G values around zero except:

The catabolism of 4 mol of glucose into 8 mol of pyruvate via glycolysis yields:

Following glycolysis, which of these molecules is NOT a possible fate of pyruvate catabolism?

In glycolysis, the reaction(s) that produce(s) NADH is?

In glycolysis, the two priming reactions (requiring ATP) are?

In comparison with the resting state, actively contracting human muscle tissue has a

Which statement about the energy production and usage in glycolysis and gluconeogenesis is correct?

The irreversible reactions of glycolysis are bypassed in gluconeogenesis using the following enzymes:

Which enzyme does NOT catalyse an irreversible reaction in either glycolysis or gluconeogenesis?