Health Quiz: Starve-Feed Cycle and its Impacts

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Questions and Answers

What role does GLUT4 play in glucose metabolism?

Facilitates glucose uptake in muscle and fat cells (correct)

Inhibits insulin production from beta cells

Increases gluconeogenesis in the liver

Regulates glycogen breakdown in the pancreas

Which factor is most directly associated with lactic acidosis?

Decreased oxygen availability in tissues (correct)

Increased pyruvate entry into the citric acid cycle

Higher levels of fructose-2,6-bisphosphate

Enhanced lactate production from gluconeogenesis

What is the primary function of the pentose phosphate pathway?

To facilitate insulin signaling in cells

To generate ATP from glucose

To provide ribose-5-phosphate for nucleotide synthesis (correct)

To convert lactate back to glucose

How does glucagon primarily affect blood glucose levels?

Promotes increased glycogenolysis and gluconeogenesis Signup and view all the answers

Which complication is commonly associated with untreated diabetes?

Atherosclerosis Signup and view all the answers

What is the primary site of gluconeogenesis?

Liver Signup and view all the answers

Which of the following tissues is noted to have a very low rate of gluconeogenesis?

Heart Muscle Signup and view all the answers

Which process involves the conversion of pyruvate to glucose?

Gluconeogenesis Signup and view all the answers

What role does glucose-6-phosphatase play in gluconeogenesis?

It is involved in the conversion of glucose-6-phosphate to glucose. Signup and view all the answers

Which pathway produces glucose for metabolic demands of tissues like the brain?

Gluconeogenesis Signup and view all the answers

In which organ does gluconeogenesis occur secondarily?

Kidney Signup and view all the answers

Which of the following is NOT a glycolytic tissue?

Liver Signup and view all the answers

What is the result of gluconeogenesis on blood glucose levels?

Maintains blood glucose levels high. Signup and view all the answers

What is a key factor in the development of Wernicke-Korsakoff syndrome besides a low vitamin B1 diet?

Low affinity of transketolase for thiamine Signup and view all the answers

What is the primary function of NADPH in the pentose phosphate pathway?

To reduce glutathione disulfide to glutathione Signup and view all the answers

What type of bond connects the components of glutathione disulfide?

Disulfide bond Signup and view all the answers

What enzyme is responsible for reducing GSSG to GSH using NADPH?

Glutathione reductase Signup and view all the answers

Which of the following statements about glutathione (GSH) is true?

The typical ratio of GSH to GSSG is around 100-1000. Signup and view all the answers

What is a necessary component for the activity of glutathione peroxidase?

Selenium Signup and view all the answers

What is the primary role of glutathione in erythrocytes?

To remove hydrogen peroxide Signup and view all the answers

Which substance has a much lower concentration in cells compared to glutathione (GSH)?

GSSG Signup and view all the answers

What is the primary enzyme involved in the conversion of pyruvate to phosphoenolpyruvate in mitochondria?

Pyruvate carboxylase Signup and view all the answers

Which of the following enzymes bypasses the irreversible reaction of phosphofructokinase in gluconeogenesis?

Phospho-fructo phosphatase Signup and view all the answers

What regulates the activity of pyruvate carboxylase in gluconeogenesis?

Acetyl-CoA Signup and view all the answers

Which of the following is inhibited by ADP in gluconeogenesis?

Phosphoenol-pyruvate carboxykinase Signup and view all the answers

Which two metabolites are each produced in the conversion of pyruvate through pyruvate carboxylase?

Oxaloacetate and CO2 Signup and view all the answers

Which enzyme is responsible for converting oxaloacetate into phosphoenolpyruvate?

Phosphoenol-pyruvate kinase Signup and view all the answers

During which metabolic process is gluconeogenesis primarily taking place?

In the mitochondria and cytosol Signup and view all the answers

What is the role of GTP in the process of gluconeogenesis?

It is a source of energy for the conversion of oxaloacetate Signup and view all the answers

What is maltose composed of?

Glucose + Glucose Signup and view all the answers

Which enzyme initiates the conversion of galactose to glucose-1P?

Galactokinase Signup and view all the answers

What condition arises from a deficiency of galactose-1P-uridyl transferase?

Galactosemia Signup and view all the answers

In galactose metabolism, which product is formed as a result of the epimerase activity?

UDP-galactose Signup and view all the answers

What is the primary treatment for individuals with galactosemia?

Exclude galactose from the diet Signup and view all the answers

How does galactose enter the glycolytic pathway?

As glucose-1P Signup and view all the answers

What is a common consequence of untreated galactosemia?

Mental retardation Signup and view all the answers

Which compound is not a product of the metabolism of maltose?

Fructose Signup and view all the answers

Study Notes

Significance of Metabolic Pathways

Cycle between starvation and feeding significantly affects body weight, diabetes, obesity, and atherosclerosis.
Impairments in cell signaling can lead to chronic diseases, including Alzheimer’s disease.

Glycemia and Glucose Metabolism

Glycemia values are important markers for diabetes management and related conditions.
Glucose enters cells via transport proteins:
- GLUT1, GLUT2, and GLUT4 play roles in different tissues.
Fructose-2,6-bisphosphate is crucial for regulating glycolysis and gluconeogenesis.

Gluconeogenesis Overview

Gluconeogenesis converts pyruvate to glucose, predominantly occurring in the liver and kidney.
Essential for maintaining blood glucose levels for tissues like the brain and muscles, which have minimal gluconeogenic activity.

Regulatory Steps in Glycolysis and Gluconeogenesis

Glycolysis has three key regulatory reactions: hexokinase, phosphofructokinase, and pyruvate kinase.
Gluconeogenesis bypasses these steps using:
- Pyruvate carboxylase
- Phosphoenolpyruvate carboxykinase (PEP-CK)
- Fructose-1,6-bisphosphatase
- Glucose-6-phosphatase

Pentose Phosphate Pathway Functions

Provides NADPH critical for biosynthetic reactions and glutathione regeneration.
Functions in two phases: oxidative phase for NADPH generation and non-oxidative phase for ribose-5-phosphate production.

Clinical Implications of Gluconeogenesis

Wernicke-Korsakoff syndrome linked to thiamine (vitamin B1) deficiency and impaired transketolase function.
Symptoms may arise from a combination of genetic factors and dietary deficiencies.

Drug-Induced Hemolytic Anemia

In erythrocytes, the pentose phosphate pathway generates NADPH necessary for converting GSSG to GSH.
GSH protects cells from oxidative damage, particularly from hydrogen peroxide, in a selenium-dependent process.

Metabolism of Disaccharides

Maltose breaks down into glucose units, which can enter glycolytic pathways.
Galactose derived from lactose needs enzymes like galactokinase and galactose-1P-uridyl transferase to be converted to glucose-1P.

Galactosemia results from a deficiency of galactose-1P-uridyl transferase, leading to galactose accumulation.
Symptoms in homozygous individuals may include liver damage, developmental issues, and cataracts.
Treatment involves dietary management by eliminating galactose sources, predominantly dairy.

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Description

Test your knowledge on the starve-feed cycle and its significance in various health conditions such as diabetes, obesity, and atherosclerosis. This quiz also covers aspects of cell signaling and their roles in diseases like Alzheimer's. Prepare to explore the links between nutrition and health!