Nutrition, Metabolism and Energy Balance

Chapter 24: Nutrition, Metabolism and Energy Balance

Overview

  • Authors: Elaine N. Marieb, Katja Hoehn

  • Prepared by: Karen Dunbar Kareiva, Ivy Tech Community College

24.1 Introduction to Nutrition and Metabolism

  • Nutrition involves the biochemical process through which organisms consume and utilize food for energy and growth.

  • Metabolism refers to all chemical reactions that occur within an organism to maintain life, which include catabolism (breaking down compounds for energy) and anabolism (building up compounds).

24.2 Key Concepts in Nutrition

  • Macronutrients: Carbohydrates, proteins, and fats that provide energy and building blocks for growth and repair.

    • Carbohydrates: Primary source of energy for the body.

    • Proteins: Composed of amino acids, essential for tissue repair and growth.

    • Fats: Important for energy storage and cell structure.

  • Micronutrients: Vitamins and minerals required in smaller amounts for various physiological functions.

    • Vitamins: Organic molecules that act as coenzymes in metabolic pathways.

    • Minerals: Inorganic elements that play critical roles in bodily functions.

24.3 Energy Balance

  • Energy balance refers to the relationship between energy intake and energy expenditure.

  • Positive Energy Balance: Consuming more energy than is expended leads to weight gain.

  • Negative Energy Balance: Expending more energy than is consumed leads to weight loss.

  • Basal Metabolic Rate (BMR): The rate at which the body expends energy at rest to maintain vital functions.

24.4 ATP Synthesis

1. Oxidative Phosphorylation

  • A complex process that produces most ATP (adenosine triphosphate).

  • This is a chemiosmotic process:

    • Mechanism: Couples the movement of protons (H+) across membranes to chemical reactions.

    • Electron Transport Chain (ETC): A series of proteins in the mitochondrial membrane that pump protons across the membrane, creating a gradient used to produce ATP.

    • High H+ concentration in the intermembrane space allows ATP synthase to generate ATP from ADP and inorganic phosphate (Pi).

    • This process occurs within the mitochondrial matrix.

2. Carbohydrate Metabolism

  • Complete Catabolism of Glucose: Requires three pathways:

    1. Glycolysis: Converts glucose to pyruvate.

    2. Krebs Cycle: Occurs in the mitochondrial matrix, oxidizing pyruvate to produce electron carriers.

    3. Electron Transport Chain and Oxidative Phosphorylation: Uses electron carriers to generate ATP.

  • Overall Reaction for Glucose Catabolism:
    C6H12O6+6O2<br>ightarrow6H2O+6CO2+32extATP+extheatC_6H_{12}O_6 + 6O_2 <br>ightarrow 6H_2O + 6CO_2 + 32 ext{ ATP} + ext{ heat}

24.5 Metabolic Pathways for Carbohydrates, Lipids, and Proteins

  • Glucose Metabolism:

    • Glycolysis, glycogenesis (formation of glycogen), glycogenolysis (breakdown of glycogen), and gluconeogenesis (formation of glucose from non-carbohydrate sources).

  • Lipid Metabolism:

    • Beta Oxidation: Converts fatty acids into acetyl-CoA.

    • Lipolysis: Breaks down stored lipids into fatty acids and glycerol.

    • Lipogenesis: Forms lipids from acetyl-CoA and glyceraldehyde 3-phosphate.

1. Oxidative Phosphorylation

  • A complex process that produces most ATP (adenosine triphosphate) in cellular respiration.

  • This is a chemiosmotic process involving several critical steps:

    • Mechanism: Couples the movement of protons (H+) across membranes to chemical reactions that generate ATP.

    • Electron Transport Chain (ETC): A series of protein complexes located in the mitochondrial membrane that transfer electrons from electron donors to electron acceptors through redox reactions.

    • The electrons come primarily from NADH and FADH2, which are produced in earlier stages of cellular respiration (like the Krebs Cycle).

    • As electrons move through the ETC, they release energy used to pump protons from the mitochondrial matrix into the intermembrane space, creating a proton gradient.

    • High concentration of protons (H+) in the intermembrane space leads to a proton motive force.

    • ATP Synthase: An enzyme that utilizes the energy from this proton gradient. Protons flow back into the matrix through ATP synthase, driving the conversion of ADP and inorganic phosphate (Pi) into ATP.

    • This process is crucial as it harnesses the energy from the electron carriers to create ATP, the primary energy currency of the cell.

  • Overall, oxidative phosphorylation allows for the efficient production of ATP, with up to 32 ATP molecules generated from a single molecule of glucose, emphasizing its importance in energy metabolism in aerobic organisms.

24.4 Carbohydrate Metabolism

  • Complete Catabolism of Glucose: Requires three pathways:

    1. Glycolysis: Converts glucose to pyruvate.

    2. Krebs Cycle: Occurs in the mitochondrial matrix, oxidizing pyruvate to produce electron carriers.

    3. Electron Transport Chain and Oxidative Phosphorylation: Uses electron carriers to generate ATP.

  • Overall Reaction for Glucose Catabolism:
    C<em>6H</em>12O<em>6+6O</em>2→6H<em>2O+6CO</em>2+32 ATP+ heatC<em>6H</em>{12}O<em>6 + 6O</em>2 \rightarrow 6H<em>2O + 6CO</em>2 + 32 \text{ ATP} + \text{ heat}

24.5 Metabolic Pathways for Carbohydrates, Lipids, and Proteins

  • Glucose Metabolism:

    • Glycolysis: Breakdown of glucose into pyruvate, which enters the Krebs Cycle.

    • Glycogenesis: Formation of glycogen from glucose for energy storage.

    • Glycogenolysis: Breakdown of glycogen back into glucose when energy is needed.

    • Gluconeogenesis: Formation of glucose from non-carbohydrate sources, ensuring stable blood sugar levels, particularly during fasting or intense exercise.

  • Lipid Metabolism:

    • Beta Oxidation: Converts fatty acids into acetyl-CoA, which can enter the Krebs Cycle for energy production.

    • Lipolysis: Breaks down stored lipids into fatty acids and glycerol, providing alternative energy sources when glucose is in short supply.

    • Lipogenesis: Forms lipids from acetyl-CoA and glyceraldehyde 3-phosphate, particularly when there is an excess of carbohydrates.

Major Macronutrients

  • Carbohydrates: Primary source of energy for the body. Found in grains, fruits, and vegetables.

  • Proteins: Composed of amino acids; essential for tissue repair and growth. Sources include meat, dairy, legumes, and nuts.

  • Fats: Important for energy storage and cell structure. Common sources are oils, butter, and fatty fish.

Neurons and Red Blood Cells

  • Neurons primarily rely on glucose for energy production.

  • Red blood cells depend on glucose since they lack mitochondria and rely on anaerobic glycolysis for ATP.

Major Micronutrients

  • Vitamins: Organic molecules acting as coenzymes; includes:

    • Vitamin A: Source includes liver, carrots, and leafy green vegetables.

    • Vitamin D: Source includes sunlight exposure, fish, and fortified milk.

    • Vitamin B: Includes a variety of sources such as whole grains, meat, and eggs.

    • Vitamin K: Sources include leafy greens and fermented foods.

  • Types:

    • Fat-soluble Vitamins: A, D, E, K.

    • Water-soluble Vitamins: B-complex and C.

Antioxidants

  • Vitamins C and E are known to be antioxidants.

Essential Minerals

  • Iron is essential for oxygen binding to hemoglobin.

Metabolism Terms

  • Anabolism: Building up processes that consume energy (synthesis of compounds).

  • Catabolism: Breaking down processes that release energy (decomposition of compounds).

Coenzymes in ATP Production

  • NAD+ and FAD act as coenzymes that accept hydrogen (or electrons) in the oxidative pathway for ATP production.

Complete Metabolism of Glucose

  1. Glycolysis: Anaerobic process converting glucose to pyruvate. Net gain of 2 ATP.

  2. Krebs Cycle: Aerobic process that produces electron carriers but no direct ATP.

  3. Electron Transport Chain and Oxidative Phosphorylation: Aerobic; produces up to 32 ATP from glucose.

    • Mechanism for ATP Production: Oxidative phosphorylation produces the most ATP during cellular respiration, as opposed to substrate level phosphorylation.

Metabolic Pathways

  • Gluconeogenesis: Formation of glucose from non-carbohydrate sources.

  • Glycogenesis: Formation of glycogen from glucose for energy storage.

  • Glycolysis: Breakdown of glucose to pyruvate.

  • Lipogenesis: Formation of lipids from acetyl-CoA.

  • Lipolysis: Breakdown of lipids into fatty acids and glycerol.

  • Transamination: Transfer of amino groups to form amino acids.

  • Oxidative Deamination: Removal of an amino group from an amino acid.

Metabolic States

  • Post-Absorptive State: Major metabolic thrust is catabolism; body's energy needs are met through stored nutrients.

  • Absorptive State: Major metabolic thrust is anabolism; nutrients from digestion are being utilized for growth and storage.

Hormonal Regulation

  • Insulin directs nearly all steps in the absorptive state.

  • Glucagon and epinephrine are primary hormones in the post-absorptive state.

Diabetes Mellitus Effects

  • Impaired glucose metabolism, resulting in high blood sugar levels, leading to potential complications in various organ systems.

Heat Production Mechanisms

  • Mechanisms include basal metabolic rate, physical activity, and thermogenesis due to food intake and environment.

Metabolic Syndrome Characteristics

  • Features include obesity, high blood pressure, high blood sugar levels, and abnormal cholesterol levels, increasing the risk of heart disease and diabetes.