Biochemistry: Gluconeogenesis Overview

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Questions and Answers

What is primarily generated during the oxidative phase of the Pentose Phosphate Pathway?

FADH2 and G-6-P

ATP and ribulose

Lactic acid and pyruvate

NADPH and a Pentose (correct)

In the context of glycolysis, which of the following statements is true regarding glucose?

It yields a significant energy amount upon oxidation. (correct)

It cannot be stored efficiently and is always utilized immediately.

Only aerobic organisms can utilize glucose.

It serves primarily as a structural component of cell walls.

Which pathway is characterized by the regeneration of G-6-P from R-5-P?

Glycolysis

Nonoxidative phase of the Pentose Phosphate Pathway (correct)

Gluconeogenesis

Krebs cycle

What is the primary end product of glycolysis?

Pyruvate Signup and view all the answers

Which of the following correctly describes the Cori cycle?

Utilizes pyruvate to regenerate glucose in the liver. Signup and view all the answers

What is the end product of the oxidative phase of the pentose phosphate pathway?

NADPH and ribulose-5-phosphate Signup and view all the answers

What reaction does 6-phospho-gluconate undergo during the pentose phosphate pathway?

Conversion to ribulose-5-phosphate Signup and view all the answers

Which tissues are primarily involved in utilizing more NADPH than ribose-5-phosphate?

Liver and adipose tissue Signup and view all the answers

Which enzyme is responsible for the conversion of 6-phospho-gluconate in the pathway?

6-phospho-gluconate dehydrogenase Signup and view all the answers

What is the primary purpose of shunting ribose-5-phosphate to glucose-6-phosphate?

To enhance energy extraction from glucose Signup and view all the answers

What is the fate of glucose in glucose-dependent cells such as red blood cells?

It is used for ATP production through glycolysis. Signup and view all the answers

Which of the following is NOT a precursor for gluconeogenesis?

Fatty acids Signup and view all the answers

What triggers a low glucose level in the body that initiates gluconeogenesis?

Release of glucagon Signup and view all the answers

What effect does the activation of fructose 2,6-bisphosphate have on phosphofructokinase 1?

It activates phosphofructokinase 1 activity. Signup and view all the answers

Which amino acids are NOT considered glucogenic?

Leucine and lysine Signup and view all the answers

What location is primarily responsible for gluconeogenesis?

The liver Signup and view all the answers

What is the main reason why fatty acids cannot be used as a source of fuel for the brain?

They do not cross the blood-brain barrier. Signup and view all the answers

Which statement about glycolysis and gluconeogenesis is true?

They operate in opposite directions and utilize different enzymes. Signup and view all the answers

What is the primary outcome of the Cori Cycle?

Conversion of glucose to lactate in the muscle, followed by reconversion to glucose in the liver Signup and view all the answers

Which of the following amino acids cannot be involved in gluconeogenesis due to their glucogenic properties?

Leucine Signup and view all the answers

What is a characteristic feature of reciprocal regulation in metabolic pathways?

One pathway is inhibited while the other is activated Signup and view all the answers

During anaerobic respiration in muscles, what is the fate of pyruvate?

It is reduced to lactic acid Signup and view all the answers

What physiological process requires a high amount of oxygen consumption to fuel its operation?

Gluconeogenesis from lactate Signup and view all the answers

What happens to lactate produced in the muscle during anaerobic conditions?

It is transported to the liver for conversion back to glucose Signup and view all the answers

What is the significance of the intermediates of the citric acid cycle in gluconeogenesis from glucogenic amino acids?

They play a role in the formation of pyruvate Signup and view all the answers

What is a direct effect of lactate accumulation in actively contracting muscles?

Decreased pH leading to muscle fatigue Signup and view all the answers

What prevents animals from producing glucose from fatty acids?

The only by-product of beta-oxidation is acetyl-CoA. Signup and view all the answers

Which of the following glycolytic steps is irreversible and cannot be used in gluconeogenesis?

Conversion of fructose-6-phosphate to fructose-1,6-bisphosphate. Signup and view all the answers

What is a characteristic feature of gluconeogenesis in comparison to glycolysis?

Gluconeogenesis is energetically expensive. Signup and view all the answers

Which enzyme catalyzes the conversion of pyruvate to oxaloacetate during gluconeogenesis?

Pyruvate carboxylase Signup and view all the answers

Which of the following statements about ATP generation in gluconeogenesis is true?

No ATP is generated during gluconeogenesis. Signup and view all the answers

What is the main precursor involved in gluconeogenesis?

Oxaloacetate Signup and view all the answers

What is the role of fructose-1,6-bisphosphatase in gluconeogenesis?

It converts fructose-1,6-bisphosphate to fructose-6-phosphate. Signup and view all the answers

Which of the following is NOT a pathway that involves irreversible steps in glycolysis?

Fructose-6-phosphate to glucose. Signup and view all the answers

Study Notes

Gluconeogenesis and Anaerobic Respiration

Gluconeogenesis converts lactate to glucose, primarily in the liver, through the Cori Cycle.
In actively contracting muscles, pyruvate is reduced to lactic acid, which may accumulate.
To prevent lactate buildup, lactate is transported to the liver for conversion to glucose, requiring high oxygen consumption.

Cori Cycle

The Cori Cycle allows for the recycling of lactate produced in muscles back to glucose in the liver.
Important for energy production during anaerobic conditions, maintaining blood glucose levels.

Gluconeogenesis from Amino Acids

Amino acids (except leucine and lysine) can be converted to glucose via gluconeogenesis.
These glucogenic amino acids contribute carbon skeletons to yield pyruvate or citric acid cycle intermediates.

Glycolysis Overview

Glycolysis is central to energy production, providing ATP through the breakdown of glucose into pyruvate.
The energetic yield of glycolysis is approximately -2840 kJ/mol glucose.

Muscle Energy Metabolism

Actively working muscles prioritize ATP use and may utilize glucose primarily.
The hormone glucagon raises cAMP levels, reducing Fructose 2,6-bisphosphate, leading to the inactivation of Phosphofructokinase 1.

Gluconeogenesis Pathway

Gluconeogenesis is energetically demanding, employing specific enzymes to bypass irreversible steps of glycolysis.
Pyruvate carboxylase converts pyruvate to oxaloacetate, then PEP-carboxykinase transforms it to phosphoenolpyruvate.
Fructose 1,6-bisphosphate is converted to fructose 6-phosphate by Fructose 1,6-bisphosphatase.

Pentose Phosphate Pathway (PPP)

The PPP has two phases: oxidative generates NADPH and ribulose-5-phosphate; nonoxidative regenerates glucose-6-phosphate from ribose-5-phosphate.
NADPH produced is vital for combating oxidative stress.

G-6-PD Deficiency

Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency can lead to issues in redox balance within cells.

Conclusion on Glucose Utilization

Glycolysis allows cells to extract energy from glucose under both aerobic and anaerobic conditions.
Fermentation is a backup energy extraction method when oxygen is limited, though less efficient than aerobic respiration.

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Description

This quiz covers the regulation of gluconeogenesis, focusing on the reciprocal reactions that involve lactate and amino acids. Understand the Cori Cycle and how glucose is converted into lactate, highlighting the role of compounds in this metabolic process.