CHO Metabolism Overview
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CHO Metabolism Overview

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Questions and Answers

What is the primary consequence of absent intestinal lactase?

  • Increased digestion of lactose
  • Enhanced lactose tolerance
  • Accumulation of lactose and fermentation (correct)
  • Immediate absorption of lactose

    • Which metabolic pathway is classified as amphibolic?

  • Gluconeogenesis
  • Glycogenolysis
  • Citric acid cycle (correct)
  • Glycolysis

    • Which of the following statements is true regarding glycolysis?

  • It occurs solely in the mitochondria.
  • It produces energy in the form of ATP. (correct)
  • It requires oxygen for both stages.
  • It takes place exclusively in skeletal muscle.

    • How many ATP molecules are consumed during the initial steps of glycolysis?

    <p>2 ATP</p> Signup and view all the answers

    What is produced as a result of anaerobic glycolysis?

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

    Which tissue is primarily dependent on glycolysis due to lack of mitochondria?

    <p>Red blood cells</p> Signup and view all the answers

    What is one significance of 2,3-biphosphoglycerate production in glycolysis?

    <p>Decreases oxygen affinity of hemoglobin</p> Signup and view all the answers

    What kind of glycolysis occurs in the presence of oxygen?

    <p>Aerobic glycolysis</p> Signup and view all the answers

    What is the net energy gain from aerobic glycolysis?

    <p>6 - 8 ATP</p> Signup and view all the answers

    Which enzyme is NOT one of the three irreversible enzymes in glycolysis?

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

    What is the role of fructose 2,6-bisphosphate in glycolysis?

    <p>Stimulates glycolysis</p> Signup and view all the answers

    In anaerobic glycolysis, how many ATP are produced from substrate level phosphorylation?

    <p>4 ATP</p> Signup and view all the answers

    How does insulin affect the key enzymes of glycolysis?

    <p>Stimulates their synthesis</p> Signup and view all the answers

    What occurs to the 2 NADH + H+ produced during anaerobic glycolysis?

    <p>They are consumed in the conversion of pyruvate to lactate</p> Signup and view all the answers

    Which of the following inhibits phosphofructokinase-1 (PFK-1)?

    <p>Citrate</p> Signup and view all the answers

    What is the fate of glycolysis in mature red blood cells (RBCs)?

    <p>Depend completely on glycolysis</p> Signup and view all the answers

    What is the primary function of anabolic pathways in metabolism?

    <p>To synthesize complex molecules from simpler ones</p> Signup and view all the answers

    Which type of metabolic pathway is primarily involved in the breakdown of complex molecules?

    <p>Catabolic pathways</p> Signup and view all the answers

    What is the effect of catabolic pathways on energy?

    <p>They release free energy</p> Signup and view all the answers

    What is a characteristic of amphibolic pathways?

    <p>They serve as a link between anabolic and catabolic pathways</p> Signup and view all the answers

    Which enzyme is responsible for converting starch and glycogen into dextrins?

    <p>Salivary amylase</p> Signup and view all the answers

    What is the product of maltase's action on maltose?

    <p>Two molecules of glucose</p> Signup and view all the answers

    What dietary source constitutes about 50% of carbohydrates consumed?

    <p>Starch</p> Signup and view all the answers

    What causes lactose intolerance?

    <p>Deficiency of the lactase enzyme</p> Signup and view all the answers

    Study Notes

    CHO Metabolism

    • CHO metabolism involves the fate of food molecules after digestion and absorption.
    • It encompasses chemical enzyme reactions inside the body, focusing on the synthesis and breakdown of various substances.

    Metabolic Pathways

    • Anabolic pathways: These pathways synthesize complex molecules from simpler ones. They require energy. A key example is protein synthesis.
    • Catabolic pathways: These pathways break down complex molecules into simpler ones. They release energy. An example is oxidative processes.
    • Amphibolic pathways: These act as links between anabolic and catabolic pathways. The citric acid cycle is an example.
    • Food molecules undergo digestion and absorption. Then they enter amphibolic pathways. Further breakdown goes to catabolic pathways to produce energy. Conversely, anabolic pathways use energy to build complex molecules.

    Carbohydrate Metabolism

    • Carbohydrates provide 50% of daily calories.
    • Complete oxidation of 1 gram of carbohydrate yields 4 kcal.
    • Sources of carbohydrates in food:
      • Starch (e.g., potatoes) makes up about 50%.
      • Sucrose and lactose comprise most of the rest.
      • Fructose and glucose come from fruits and honey.

    Digestion of Carbohydrates

    • Polysaccharides and disaccharides must be broken down into monosaccharides (e.g., glucose) to be absorbed.
    • Key enzymes involved in this process include:
      • Salivary amylase: breaks down starch and glycogen into dextrins.
      • Pancreatic amylase: converts dextrins into maltose.
      • Intestinal disaccharidases:
        • Maltase converts maltose into glucose.
        • Sucrase converts sucrose into glucose and fructose.
        • Lactase converts lactose into glucose and galactose.

    Lactose Intolerance

    • Definition: A disease (congenital or acquired) caused by lactase enzyme deficiency.
    • Cause: Insufficient lactase enzyme.
    • Effects: Undigested lactose accumulates in the intestine, leading to fermentation by intestinal bacteria, producing acids and gases.
    • Symptoms: Abdominal distension, cramps, and diarrhea (due to increased intestinal osmotic pressure).
    • Treatment: Lactose-free milk formulas.

    Metabolic Pathways of Carbohydrates

    • Catabolic pathways:
      • Glycolysis (glucose oxidation to pyruvate or lactate)
      • Pentose phosphate shunt
      • Uronic acid pathway
      • Glycogenolysis (glycogen breakdown)
    • Anabolic pathways:
      • Gluconeogenesis (gluconeogenesis)
      • Glycogenesis (glycogen synthesis)
    • Amphibolic pathways:
      • Citric acid cycle

    Glycolysis

    • Definition: The oxidation of glucose to pyruvate (in the presence of oxygen) or lactate (in the absence of oxygen).
    • Site: Occurs in the cytoplasm of all tissue cells, crucial for tissues without mitochondria (e.g., red blood cells) and those with frequent oxygen deficiency (e.g., muscles during exercise).
    • Steps:
      • Stage 1 (energy-requiring): Glucose is converted into glyceraldehyde-3-phosphate. Energy is consumed.
      • Stage 2 (energy-producing): Glyceraldehyde-3-phosphate is converted to pyruvate or lactate. Energy is produced.

    Importance of Glycolysis

    • Key energy production process: anaerobically (2 ATP) and aerobically (6-8 ATP).
    • Major pathway for fructose and galactose metabolism.
    • Good oxygenation of tissues: 2,3-biphosphoglycerate decreases hemoglobin's affinity for oxygen.
    • Source of important intermediates such as dihydroxyacetone phosphate (for lipogenesis) and pyruvate (for amino acid synthesis).

    Energy Production in Glycolysis

    • Aerobic glycolysis:
      • 4 ATP from substrate-level phosphorylation.
      • Additional 6-8 ATP from the electron transport chain (from oxidizing NADH).
    • Anaerobic glycolysis:
      • 2 ATP from substrate-level phosphorylation.

    Glycolysis in Red Blood Cells

    • Mature red blood cells lack mitochondria, thus relying entirely on glycolysis for energy.
    • The end product is lactate.
    • The net energy yield is 2 ATP.
    • Glucose uptake by red blood cells is independent of insulin.
    • 2,3-BPG is produced.

    Regulation of Glycolysis

    • Key enzymes (hexokinase/glucokinase, phosphofructokinase-1, and pyruvate kinase) are regulated hormonally and allosterically.
    • Hormonal regulation: Insulin stimulates enzyme synthesis; glucagon inhibits it.
    • Allosteric regulation: G-6-P inhibits hexokinase, fructose 2,6-bisphosphate stimulates phosphofructokinase-1, and citrate inhibits phosphofructokinase-1. Fructose 2,6-biphosphate stimulates pyruvate kinase.
    • Covalent modification: Pyruvate kinase is inactivated by phosphorylation.
    • Energy regulation: ADP and AMP stimulate phosphofructokinase-1, and ATP inhibits phosphofructokinase-1 and pyruvate kinase.

    Inhibition of Glycolysis

    • In vitro:
      • Arsenate competes with inorganic phosphate.
      • Iodoacetate inhibits glyceraldehyde 3-phosphate dehydrogenase.
      • Fluoride inhibits enolase.
    • Important: Hemolytic anemia is often caused by pyruvate kinase deficiency.

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    CHO Metabolism Lecture 1 PDF

    Description

    This quiz explores the metabolism of carbohydrates, detailing their digestion, absorption, and the biochemical pathways involved. Learn about anabolic, catabolic, and amphibolic pathways that dictate how food molecules are processed in the body.

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