Glycolysis and Gluconeogenesis Quiz

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Questions and Answers

Which enzyme is responsible for converting 2-Phosphoglycerate to Phosphoenolpyruvate?

Pyruvate Kinase

Aldolase

Enolase (correct)

Phosphoglycerate Kinase

In which step of glycolysis is ATP synthesized for the first time, resulting in a net gain of ATP?

Step 7

Step 10 (correct)

Step 3

Step 1

Which of the following is NOT an allosteric activator of pyruvate kinase?

ATP (correct)

AMP

Acetyl-CoA (correct)

Fructose-1,6-bisphosphate

Which step in glycolysis involves a change in carbon chain length?

Step 4 (C) Signup and view all the answers

What is the main purpose of step 8 in glycolysis?

Prepare for the next step (B) Signup and view all the answers

Which of the following steps in glycolysis produces NADH?

Step 6 (C) Signup and view all the answers

Why is the conversion of 2-Phosphoglycerate to Phosphoenolpyruvate important in glycolysis?

It generates a high-energy phosphate bond (A) Signup and view all the answers

What is the net gain of ATP molecules per glucose molecule in glycolysis?

2 (C) Signup and view all the answers

What is the fate of pyruvate under aerobic conditions?

Pyruvate is oxidized completely to CO2 and H2O. (C) Signup and view all the answers

What is the primary role of NADH in glycolysis?

To regenerate NAD+ for continued glycolysis. (C) Signup and view all the answers

Which of the following molecules is NOT a precursor to glucose in gluconeogenesis?

Fatty acids (C) Signup and view all the answers

How does gluconeogenesis differ from the reverse of glycolysis?

Gluconeogenesis uses different enzymes than glycolysis. (D) Signup and view all the answers

Why is gluconeogenesis considered a costly process?

It requires significant energy investment in the form of ATP and GTP. (A) Signup and view all the answers

What is the role of the malate-aspartate shuttle in gluconeogenesis?

To transport oxaloacetate from the mitochondria to the cytoplasm. (B) Signup and view all the answers

How does lactate contribute to gluconeogenesis?

Lactate is oxidized to pyruvate, which can then enter gluconeogenesis. (B) Signup and view all the answers

What is the primary regulatory mechanism for gluconeogenesis?

The presence of insulin and glucagon hormones. (C) Signup and view all the answers

What is the key difference between step 8 of gluconeogenesis and step 3 of glycolysis?

Step 8 of gluconeogenesis uses a phosphatase enzyme, while step 3 of glycolysis uses a kinase enzyme. (B) Signup and view all the answers

Which of the following is NOT a key characteristic of the pentose phosphate pathway?

It directly generates ATP through substrate-level phosphorylation. (D) Signup and view all the answers

Which of the following molecules is a precursor for nucleotide synthesis?

Ribose-5-phosphate (A) Signup and view all the answers

Why is the conversion of glucose-6-phosphate to glucose an exergonic reaction in step 10 of gluconeogenesis?

The reaction is catalyzed by a phosphatase enzyme, which removes a phosphate group. (A) Signup and view all the answers

What is the significance of the conversion of glucose-6-phosphate to glucose taking place within the ER of liver and kidney cells?

This facilitates the efficient transport of glucose to other tissues. (B) Signup and view all the answers

What is the main purpose of the preparatory phase in glycolysis?

To prepare glucose for cleavage into two 3-carbon molecules (C) Signup and view all the answers

What is the role of hexokinase in glycolysis?

To phosphorylate glucose at C-6 (B) Signup and view all the answers

Why is the first step of glycolysis considered irreversible?

Because the reaction is highly exergonic (A) Signup and view all the answers

What is the primary function of the payoff phase in glycolysis?

To generate ATP and NADH (A) Signup and view all the answers

Under anaerobic conditions, what happens to pyruvate?

It is converted to lactate (D) Signup and view all the answers

What is the role of NAD+ in glycolysis?

To carry electrons from glucose to the electron transport chain (B) Signup and view all the answers

Which of the following statements correctly describes the energy balance of glycolysis?

Glycolysis produces a net gain of 2 ATP molecules (D) Signup and view all the answers

Which of the following statements about the conversion of glucose-6-phosphate to fructose-6-phosphate in glycolysis is incorrect?

It is a step that involves the cleavage of a carbon-carbon bond. (B) Signup and view all the answers

What is the primary role of phosphofructokinase-1 (PFK-1) in glycolysis?

To phosphorylate fructose-6-phosphate and commit the molecule to glycolysis. (C) Signup and view all the answers

Which of the following is NOT a product of glycolysis?

Acetyl-CoA (D) Signup and view all the answers

What is the primary reason why the conversion of dihydroxyacetone phosphate (DHAP) to glyceraldehyde-3-phosphate (G-3-P) is important in glycolysis?

It allows for the production of two molecules of glyceraldehyde-3-phosphate from one molecule of glucose. (C) Signup and view all the answers

Which of the following statements correctly describes the energy changes that occur during the first half of glycolysis?

Two ATP molecules are consumed, and no ATP is produced. (A) Signup and view all the answers

How does the phosphorylation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate contribute to the production of ATP in glycolysis?

It creates a high-energy phosphate bond that can later be used to generate ATP. (A) Signup and view all the answers

Which of the following enzymes is responsible for catalyzing the irreversible commitment step of glycolysis?

Phosphofructokinase-1 (PFK-1) (B) Signup and view all the answers

Which of the following enzymes in glycolysis is a regulatory enzyme that is subject to feedback inhibition?

Hexokinase (B) Signup and view all the answers

In step 7 of glycolysis, how many molecules of ATP are generated?

2 (D) Signup and view all the answers

Which of the following reactions is most likely to be endergonic?

Step 4: Fructose-6-phosphate to Fructose-1,6-bisphosphate (A) Signup and view all the answers

Which of the following statements is TRUE regarding the regulation of glycolysis?

Glycolysis is regulated by multiple enzymes and is influenced by the cell's energy needs. (B) Signup and view all the answers

Which of the following is NOT a pathway that can feed into glycolysis?

Breakdown of fatty acids (B) Signup and view all the answers

In step 6, how many molecules of NADH are produced?

2 (B) Signup and view all the answers

Which of the following statements is TRUE about the standard free energy change (Delta G) for glycolysis reactions?

Some reactions in glycolysis are exergonic, while others are endergonic, and the overall process is exergonic. (C) Signup and view all the answers

Which type of reaction is catalyzed by enolase in step 9 of glycolysis?

Dehydration (A) Signup and view all the answers

Study Notes

Carbohydrate Metabolism

Carbohydrates are a major fuel source for organisms.
Complete oxidation of glucose releases ~2,840 kJ/mol of energy.
Glucose can be used to synthesize the carbon skeletons of many other molecules.
In plants and animals, glucose can be stored as polysaccharides (e.g., glycogen, starch) or sucrose.
Glucose can be oxidized to a 3-carbon compound (pyruvate) via glycolysis.
Glucose can be oxidized to pentoses (used in nucleic acid synthesis).

Outline of the Section

Carbohydrates: nutritional perspective
Metabolism of carbohydrates
Metabolism of carbohydrates: nutritional perspective

Glucose

Major fuel source for most organisms.
Oxidation yields approximately -2,840 kJ/mol of energy
Precursor for many molecules
Stored in higher plants and animals as polysaccharides like sucrose.
Oxidized to pyruvate via glycolysis.
Oxidized to pentoses for nucleic acid synthesis

Fates of Glucose

Synthesis of structural polysaccharides for cell walls of bacteria and plants and extracellular matrix components.
Synthesis of structural polymers (e.g., cell wall polysaccharides)
Oxidation via pentose phosphate pathway (generates NADPH, used in biosynthesis of lipids & nucleotides)
Oxidation via Glycolysis (production of ATP and pyruvate)
Storage (glycogen, starch) for later energy needs

Glycolysis

Almost universal pathway for carbohydrate catabolism.
Stores energy in ATP and NADH.
Anaerobic or aerobic catabolism of glucose.
Two-phase process: investment and payoff phases.
Net gain of 2 ATP per glucose molecule.

Fates of Pyruvate

Aerobic conditions: Pyruvate is oxidized to acetyl-CoA, which enters the citric acid cycle.
Anaerobic conditions (e.g., animals, microbes): Pyruvate converted to lactate to regenerate NAD+ which is needed to continue glycolysis (lactic acid fermentation)

Summary of Glycolysis and Energetics

5.2% of glucose energy is removed in glycolysis (oxidation-reduction only).
Much energy remains in pyruvate for further oxidation.
Glycolysis: Glucose + 2ADP + 2NAD+ → 2Pyruvate + 2ATP + 2NADH + 2H+ + 2H₂O
Net reaction: Glucose + 2NAD+ +2ADP + 2Pi → 2 Pyruvate + 2NADH + 2H+ + 2ATP + 2H₂O

Glycolysis: Steps 1-10 (Detailed)

Each section (1-10) outlines individual enzymatic steps during glycolysis, highlighting the inputs, outputs, reaction types (exergonic or endergonic), involved enzymes, thermodynamic parameters, and regulation details.

Other Pathways Can Lead to the Glycolysis Pathway

Multiple pathways feed into glycolysis, including those involving disaccharides (e.g., sucrose, lactose) and polysaccharides (e.g., starch, glycogen).
These pathways break down complex carbohydrates into single sugars that can enter glycolysis.

Monosaccharide Feed-in to Glycolysis

Many monosaccharides like fructose, mannose, and galactose can be converted into glucose or glycolysis intermediates.

Anaerobic Metabolism (Pyruvate to Lactate)

During vigorous exercise when oxygen supply is limited, lactate is formed from pyruvate.
This regenerates NAD+ needed for glycolysis
The accumulation of lactate leads to muscle pain.

Anaerobic Metabolism (Pyruvate to Ethanol)

In some microorganisms (yeast), pyruvate is decarboxylated to acetaldehyde, then to ethanol.
This regenerates NAD+ needed for glycolysis.

From Catabolism to Anabolism

Convergent catabolic pathways and divergent anabolic pathways often share related intermediates.
ATP, NADH/NADPH are common precursors.

Carbohydrate Biosynthesis

Focuses on how human (animal) cells synthesize carbohydrates, including glucose formation from various precursors.
Pathways like gluconeogenesis convert lactate, amino acids, and other compounds into glucose

Gluconeogenesis

Synthesis of glucose from non-carbohydrate precursors (e.g., lactate, amino acids, oxaloacetate).
Bypass steps in the glycolysis reaction are used.
The process consumes energy.