Carbohydrate Metabolism and Glycolysis
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Questions and Answers

What are the primary end products of glycolysis under aerobic conditions?

Pyruvate is the primary end product of glycolysis under aerobic conditions.

Describe the role of GLUT4 in glucose metabolism.

GLUT4 facilitates glucose transport into adipose tissue and skeletal muscle, and its activity is regulated by insulin.

What distinguishes aerobic glycolysis from anaerobic glycolysis?

Aerobic glycolysis produces pyruvate, while anaerobic glycolysis produces lactate when oxygen is scarce.

What is the significance of the pentose phosphate pathway in carbohydrate metabolism?

<p>The pentose phosphate pathway is important for generating NADPH and ribose-5-phosphate for biosynthesis.</p> Signup and view all the answers

How does glucose enter liver cells compared to other tissues?

<p>In liver cells, glucose enters via facilitated diffusion, which is insulin-independent, unlike in other tissues where it is insulin-dependent.</p> Signup and view all the answers

What is the role of pyruvate in glucose metabolism?

<p>Pyruvate acts as a key intermediate in glucose metabolism, either entering the citric acid cycle or being converted to lactate under anaerobic conditions.</p> Signup and view all the answers

What are the key reactions involved in glycolysis?

<p>Glycolysis involves reactions such as phosphorylation, cleavage, and oxidation, mediated by specific enzymes.</p> Signup and view all the answers

Explain the importance of gluconeogenesis in carbohydrate metabolism.

<p>Gluconeogenesis is crucial for maintaining blood glucose levels during fasting or intense exercise by synthesizing glucose from non-carbohydrate precursors.</p> Signup and view all the answers

What is the terminal oxidation product generated from the oxidation of fatty acids with an odd number of carbon atoms?

<p>Propionyl-CoA</p> Signup and view all the answers

How does gluconeogenesis affect glucose supply during fasting and starvation?

<p>It meets the glucose requirement of the body when carbohydrates are in short supply.</p> Signup and view all the answers

What two substances produced by other tissues can gluconeogenesis convert into glucose?

<p>Lactate and glycerol</p> Signup and view all the answers

What is the role of the enzyme propionyl-CoA carboxylase in the conversion of propionyl-CoA?

<p>It converts propionyl-CoA to succinyl-CoA and requires ATP.</p> Signup and view all the answers

What are the key allosteric regulators of pyruvate carboxylase?

<p>Acetyl-CoA activates it.</p> Signup and view all the answers

How does insulin affect gluconeogenesis?

<p>Insulin decreases the synthesis of key enzymes of gluconeogenesis, inhibiting the process.</p> Signup and view all the answers

What is the significance of maintaining blood glucose levels in the range of 5 mm/L?

<p>It ensures that organs, especially the brain, receive a consistent supply of glucose.</p> Signup and view all the answers

How does fructose-1, 6-bisphosphatase regulate gluconeogenesis?

<p>AMP acts as an allosteric inhibitor of fructose-1, 6-bisphosphatase.</p> Signup and view all the answers

What are the irreversible steps of glycolysis?

<p>The irreversible steps of glycolysis include the reactions catalyzed by hexokinase, phosphofructokinase, and pyruvate kinase.</p> Signup and view all the answers

Describe how hexokinase regulates glycolysis.

<p>Hexokinase catalyzes the phosphorylation of glucose to glucose-6-phosphate, an irreversible reaction that commits glucose to glycolysis.</p> Signup and view all the answers

What distinguishes glucokinase from hexokinase in the liver?

<p>Glucokinase is an inducible enzyme with a higher Km for glucose, functioning only at high blood glucose concentrations, unlike hexokinase which is widely distributed and has a lower Km.</p> Signup and view all the answers

How many ATP molecules are generated during aerobic glycolysis?

<p>Aerobic glycolysis generates a net total of 7 ATP molecules.</p> Signup and view all the answers

What happens to NADH produced during anaerobic glycolysis?

<p>NADH is used to convert pyruvate to lactate, regenerating NAD+ needed for continued glycolysis.</p> Signup and view all the answers

Explain the significance of the ATP yield difference between aerobic and anaerobic glycolysis.

<p>Aerobic glycolysis generates substantially more ATP per mole of glucose (7 ATP) compared to anaerobic glycolysis (2 ATP).</p> Signup and view all the answers

What role does pyruvate kinase play in glycolysis?

<p>Pyruvate kinase catalyzes the conversion of phosphoenolpyruvate to pyruvate, generating 2 ATP in the process.</p> Signup and view all the answers

What are the outcomes of glycolysis in aerobic and anaerobic conditions?

<p>In aerobic conditions, glycolysis produces pyruvate and generates 7 ATP, while in anaerobic conditions, it produces lactate and generates 2 ATP.</p> Signup and view all the answers

What role does insulin play in glucose homeostasis?

<p>Insulin regulates plasma glucose levels by promoting glucose uptake in adipose and muscle cells and stimulating glycogen synthesis.</p> Signup and view all the answers

How does glucagon act to raise blood glucose levels?

<p>Glucagon increases blood glucose by stimulating hepatic glycogenolysis and gluconeogenesis.</p> Signup and view all the answers

What is the relationship between growth hormone and glucose uptake in tissues?

<p>Growth hormone inhibits glucose uptake in extrahepatic tissues, especially in muscles, which increases blood glucose levels.</p> Signup and view all the answers

In what situation is cortisol released and what effect does it have on glucose metabolism?

<p>Cortisol is released in response to stress and hypoglycemia, increasing blood glucose by inhibiting glucose uptake and enhancing gluconeogenesis.</p> Signup and view all the answers

What are the consequences of insulin receptor dysfunction on glucose homeostasis?

<p>Dysfunction of insulin receptors can lead to inadequate glucose uptake, resulting in persistently high plasma glucose levels.</p> Signup and view all the answers

Describe the physiological role of adrenaline in glucose homeostasis.

<p>Adrenaline stimulates glycogenolysis in the liver and muscle, increasing glucose availability during stressful situations.</p> Signup and view all the answers

What is the pentose phosphate pathway (PPP) and its primary function?

<p>The pentose phosphate pathway is a metabolic pathway that generates NADPH and ribose-5-phosphate for anabolic reactions.</p> Signup and view all the answers

Why is adequate insulin secretion important for combating hyperglycemia?

<p>Adequate insulin secretion is essential to facilitate glucose uptake and reduce plasma glucose levels effectively.</p> Signup and view all the answers

What are the two major phases of the pentose phosphate pathway?

<p>The two major phases are the oxidative arm, which generates NADPH, and the non-oxidative arm, which produces ribose-5-phosphate.</p> Signup and view all the answers

What is the primary function of the pentose phosphate pathway?

<p>The main functions are to generate NADPH for biosynthetic reactions and to provide ribose-5-phosphate for nucleotide synthesis.</p> Signup and view all the answers

How does the pentose phosphate pathway relate to dietary pentose sugars?

<p>The pathway metabolizes dietary pentose sugars derived from nucleic acids and rearranges carbon skeletons into glycolytic intermediates.</p> Signup and view all the answers

Where in the body is the pentose phosphate pathway most active?

<p>The PPP is most active in the liver, adipose tissue, erythrocytes, and certain glands, while less active in skeletal muscle.</p> Signup and view all the answers

What role does glucose-6-phosphate dehydrogenase play in the pentose phosphate pathway?

<p>Glucose-6-phosphate dehydrogenase catalyzes the first reaction in the oxidative phase, generating NADPH.</p> Signup and view all the answers

What is Glucose-6-Phosphate Dehydrogenase Deficiency and its impact on health?

<p>G6PDD is a genetic condition where patients have reduced activity of the enzyme, leading to vulnerability to hemolytic anemia when exposed to certain drugs.</p> Signup and view all the answers

Describe the oxidative and non-oxidative reactions of the pentose phosphate pathway.

<p>The oxidative reactions convert glucose-6-phosphate into NADPH, while the non-oxidative reactions rearrange sugar phosphates to produce ribose-5-phosphate.</p> Signup and view all the answers

How does the pentose phosphate pathway contribute to the maintenance of glutathione in red blood cells?

<p>The pathway provides NADPH, which is essential for keeping glutathione in its reduced state, protecting cells from oxidative damage.</p> Signup and view all the answers

Study Notes

Carbohydrate Metabolism

  • Digestion and Absorption of Dietary CHO:
    • Simple carbohydrates are absorbed by the small intestine.
    • Absorbed carbohydrates are transported to the liver and other tissues.
    • They are either converted into fatty acids, amino acids, or glycogen.
    • Alternatively, they are oxidized through catabolic pathways.

Glucose Metabolism (Glycolysis)

  • Definition:
    • Glycolysis is the oxidation of glucose to either pyruvate or lactate.
    • It is a catabolic pathway.
    • Aerobic glycolysis produces pyruvate in the presence of oxygen.
    • Anaerobic glycolysis produces lactate in the absence of oxygen.
  • Key Enzymes:
    • Hexokinase: Initiates glycolysis by phosphorylating glucose.
    • Glucokinase: Found in the liver, phosphorylates glucose only when blood glucose levels are high.
  • Regulation:
    • Hexokinase: Allosterically regulated; irreversible.
    • Glucokinase: Inducible enzyme with a high Km for glucose.
  • Energetics:
    • Aerobic glycolysis: Net yield of 7 ATP molecules per glucose molecule.
    • Anaerobic glycolysis: Net yield of 2 ATP molecules per glucose molecule.
  • Fate of Pyruvate:
    • Aerobic glycolysis: Pyruvate enters the citric acid cycle.
    • Anaerobic glycolysis: Pyruvate is converted to lactate.

Citric Acid Cycle

  • Definition:
    • A series of biochemical reactions that oxidize acetyl-CoA to carbon dioxide and water.
  • Importance:
    • Generates ATP through oxidative phosphorylation.
    • Provides precursors for biosynthesis pathways.

Gluconeogenesis

  • Definition:
    • The process of synthesizing glucose from non-carbohydrate precursors, primarily pyruvate, lactate, glycerol, and glucogenic amino acids.
    • It is an anabolic pathway.
  • Importance:
    • Maintains blood glucose levels during fasting.
    • Supplies glucose to tissues like the brain.
    • Clears metabolic products from the blood.
  • Regulation:
    • Allosteric regulation:
      • Acetyl-CoA activates pyruvate carboxylase.
      • AMP inhibits fructose-1,6-bisphosphatase.
    • Hormonal regulation:
      • Insulin inhibits gluconeogenesis.

Glycogen Metabolism

  • Definition:
    • The process of synthesizing and breaking down glycogen, the storage form of glucose in animals.
  • Glycogenesis:
    • The synthesis of glycogen from glucose.
  • Glycogenolysis:
    • The breakdown of glycogen into glucose.
  • Regulation:
    • Insulin: Stimulates glycogen synthesis.
    • Glucagon: Stimulates glycogen breakdown.

Blood Glucose Homeostasis

  • Regulation:
    • Insulin:
      • Secreted by pancreatic β-cells in response to hyperglycemia.
      • Promotes glucose uptake by cells, glycogen synthesis, and inhibits gluconeogenesis.
    • Glucagon:
      • Secreted by pancreatic α-cells in response to hypoglycemia.
      • Stimulates glycogen breakdown and gluconeogenesis.
    • Growth Hormone:
      • Released from the pituitary gland.
      • Inhibits glucose uptake, promotes lipolysis, and increases protein synthesis.
    • Glucocorticoids:
      • Released from the adrenal cortex.
      • Inhibit glucose uptake, promote gluconeogenesis, and increase lipolysis.
    • Adrenaline:
      • Released from the adrenal medulla in response to stress.
      • Stimulates glycogen breakdown and lipolysis.

Pentose Phosphate Pathway (PPP)

  • Definition:
    • An alternative pathway for glucose metabolism that generates NADPH and ribose-5-phosphate.
    • Primarily an anabolic pathway.
  • Functions:
    • Provides NADPH for reductive biosynthesis.
    • Synthesizes ribose-5-phosphate for nucleotide and nucleic acid synthesis.
    • Metabolizes dietary pentose sugars.
  • Medical Importance:
    • Glucose-6-Phosphate Dehydrogenase Deficiency (G6PDD):
      • A genetic deficiency that affects the activity of glucose-6-phosphate dehydrogenase (G6PD).
      • Can lead to hemolytic anemia due to oxidative stress in erythrocytes when individuals are exposed to certain drugs or infections.
      • NADPH deficiency in erythrocytes results in reduced glutathione levels, increasing oxidative stress.

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Description

This quiz explores the digestion, absorption, and metabolic pathways of carbohydrates, focusing on glycolysis. Participants will learn about key enzymes and their regulation in glucose metabolism, as well as the differences between aerobic and anaerobic glycolysis.

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