ch25

Overview of Metabolism, Nutrition, and Energetics

• Metabolism: Sum of all chemical and physical changes that occur in body tissues.

  • Comprises catabolism (breakdown of molecules) and anabolism (synthesis of molecules).

  • Nutrient Pool: All available nutrient molecules in the blood.

Metabolic Activity and ATP Production

• ATP (Adenosine Triphosphate): Energy currency of the cell, produced primarily in mitochondria.

• Key requirements to produce ATP:

  • Oxygen

  • Nutrients: Water, vitamins, mineral ions, organic substrates.

Catabolism and Anabolism

• Catabolism: Converts large molecules into smaller ones; releases energy to synthesize ATP.

  • Example: Breakdown of glucose during glycolysis.

• Anabolism: Converts small molecules into larger molecules; forms new chemical bonds and requires energy.

  • Functions include structural maintenance, growth support, secretion production, and nutrient reserve storage.

Nutrient Reserves

• Triglycerides: Most abundant storage lipids (fatty acids).

• Glycogen: Most abundant storage carbohydrate (branched chain of glucose molecules).

• Proteins: Most abundant organic components, performing vital cellular functions.

Energetics and Energy Transfer

• Energetics: Study of energy flow and its transformation.

• Oxidation-Reduction Reactions:

  • Oxidation: Loss of electrons or hydrogen; energy is released.

  • Reduction: Gain of electrons or hydrogen; energy is absorbed.

  • These reactions are coupled, leading to the concept of redox reactions.

Electron Transport Chain (ETC)

• Series of protein complexes in the mitochondria where electrons are passed through oxidation-reduction reactions.

  • Energy loss from electrons is used to synthesize ATP.

  • Final electron acceptor is oxygen, producing water as a by-product.

Coenzymes in Energy Flow

• Coenzymes assist in electron transport:

  • NAD (Nicotinamide adenine dinucleotide): Accepts two hydrogen atoms forming NADH.

  • FAD (Flavin adenine dinucleotide): Accepts two hydrogen atoms forming FADH2.

Glycolysis and Aerobic Metabolism

• Glycolysis: Anaerobic breakdown of glucose into two pyruvate molecules, yielding a net gain of 2 ATP.

• Aerobic Metabolism: Occurs in mitochondria, involving the citric acid cycle and electron transport chain, yielding up to 30–32 ATP per glucose molecule.

Citric Acid Cycle (Krebs Cycle)

• Removes hydrogens from pyruvate, yielding CO2, NADH, and acetyl-CoA.

• Each cycle yields one GTP (which can be converted to ATP) and generates electron carriers (NADH and FADH2).

Oxidative Phosphorylation

• Process of generating ATP from NADH and FADH2 as electrons transfer to oxygen via the ETC.

  • Yield of ATP from NADH is approximately 2.5, and from FADH2 is about 1.5.

Summary of ATP Production

• Total ATP gain from one glucose: 30–32 ATP.

  • Steps include ATP from glycolysis, citric acid cycle, and oxidative phosphorylation.

Lipid Metabolism

• Lipid Catabolism: Breakdown of triglycerides into glycerol and fatty acids; beta-oxidation converts fatty acids into acetyl-CoA.

• Lipids provide more ATP than carbohydrates (120 ATP from an 18-carbon fatty acid).

Protein Metabolism

• Body synthesizes proteins from 20 amino acids.

• Amino acids must undergo deamination and transamination to enter the citric acid cycle for energy production.

Absorptive and Postabsorptive States

• Absorptive State: Nutrient absorption occurs for about 4 hours after eating.

• Postabsorptive State: Body relies on internal reserves to maintain blood glucose levels, using lipids and amino acids primarily.

Nutrition and Dietary Needs

• Balanced diet essential for homeostasis and includes macronutrients and micronutrients.

• Malnutrition: Resulting from nutrient imbalance. Balanced intake from food groups is recommended (MyPlate).

Metabolic Rate and Thermoregulation

• Metabolic Rate: Average caloric expenditure affected by activity, age, sex, and hormones.

• Thermoregulation: Mechanisms to maintain body temperature include metabolism regulation, heat exchange processes, and behavioral adjustments.

Mechanisms of Heat Exchange

• Radiation, Convection, Evaporation, Conduction: Diverse processes through which body exchanges heat with the environment.

• Body maintains temperature through responses coordinated by the hypothalamus.

Conclusion

• Energy metabolism is a complex interaction of biochemical pathways. It encompasses how organisms utilize nutrients, regulate energy balance, and maintain homeostasis.

Overview of Metabolism, Nutrition, and Energetics

• Metabolism: Sum of all chemical and physical changes that occur in body tissues, critical for sustaining life.

• Comprises catabolism (breakdown of molecules) and anabolism (synthesis of molecules), both vital for growth and repair of tissues.

• Nutrient Pool: All available nutrient molecules in the blood, which serve as substrates for metabolic processes.

Metabolic Activity and ATP Production

• ATP (Adenosine Triphosphate): Energy currency of the cell, essential for many cellular processes, produced primarily in mitochondria.

• Key requirements to produce ATP:

  • Oxygen: Necessary for aerobic respiration.

  • Nutrients: Water, vitamins, mineral ions, organic substrates necessary for metabolic reactions.

Catabolism and Anabolism

• Catabolism: Converts large molecules into smaller ones (e.g., glucose to pyruvate); releases energy to synthesize ATP, crucial for energy demands during exertion.

  • Example: Breakdown of glucose during glycolysis, which occurs in the cytoplasm.

• Anabolism: Converts small molecules into larger molecules (e.g., amino acids to proteins); requires energy and is involved in biosynthetic pathways for macromolecules.

  • Functions include structural maintenance, growth support, secretion production, and nutrient reserve storage.

Nutrient Reserves

• Triglycerides: Most abundant storage lipids, serving as a compact energy source (fatty acids) for long-term energy needs.

• Glycogen: Most abundant storage carbohydrate, a branched chain of glucose molecules, primarily found in the liver and muscles, providing a quick energy reserve.

• Proteins: Most abundant organic components of the body, performing vital cellular functions including enzymatic catalysis, structural support, and transport.

Energetics and Energy Transfer

• Energetics: Study of energy flow and its transformation in biological systems, crucial for understanding metabolic pathways.

• Oxidation-Reduction Reactions:

  • Oxidation: Loss of electrons or hydrogen; energy is released, often linked to energy-producing pathways.

  • Reduction: Gain of electrons or hydrogen; energy is absorbed, important for biosynthetic reactions.

  • These reactions are coupled, leading to the concept of redox reactions, foundational in energy metabolism.

Electron Transport Chain (ETC)

• A series of protein complexes in the mitochondria where electrons are passed through oxidation-reduction reactions.

• Energy loss from electrons is utilized to synthesize ATP, highlighting the coupling of electron transport and ATP synthesis.

• Final electron acceptor is oxygen, producing water as a by-product, essential for maintaining cellular respiration.

Coenzymes in Energy Flow

• Coenzymes assist in electron transport:

  • NAD (Nicotinamide adenine dinucleotide): Accepts two hydrogen atoms forming NADH, playing a crucial role in energy metabolism.

  • FAD (Flavin adenine dinucleotide): Accepts two hydrogen atoms forming FADH2, also vital in energy production pathways.

Glycolysis and Aerobic Metabolism

• Glycolysis: Anaerobic breakdown of glucose into two pyruvate molecules, yielding a net gain of 2 ATP, occurs in the cytoplasm and does not require oxygen.

• Aerobic Metabolism: Occurs in mitochondria, involving the citric acid cycle and electron transport chain; can yield up to 30–32 ATP per glucose molecule, showing high efficiency in ATP production.

Citric Acid Cycle (Krebs Cycle)

• Removes hydrogens from pyruvate, yielding CO2, NADH, and acetyl-CoA, which is a critical metabolite in energy production.

• Each cycle yields one GTP (which can be converted to ATP) and generates electron carriers (NADH and FADH2), crucial for subsequent steps in ATP synthesis.

Oxidative Phosphorylation

• Process of generating ATP from NADH and FADH2 as electrons transfer to oxygen via the ETC, critical for the majority of ATP production in cells.

• Yield of ATP from NADH is approximately 2.5, and from FADH2 is about 1.5, highlighting differences in energy contribution across different substrates.

Summary of ATP Production

• Total ATP gain from one glucose molecule is 30–32 ATP, covering all pathways from glycolysis, citric acid cycle, and oxidative phosphorylation, showcasing cellular energy harvesting efficiency.

Lipid Metabolism

• Lipid Catabolism: Breakdown of triglycerides into glycerol and fatty acids; beta-oxidation converts fatty acids into acetyl-CoA for energy production.

• Lipids provide more ATP than carbohydrates, with approximately 120 ATP derived from the complete oxidation of an 18-carbon fatty acid, demonstrating their importance as an energy source.

Protein Metabolism

• Body synthesizes proteins from 20 amino acids, crucial for cellular structure and function.

• Amino acids must undergo deamination and transamination to enter the citric acid cycle for energy production, linking protein metabolism to energy metabolism.

Absorptive and Postabsorptive States

• Absorptive State: Occurs for about 4 hours after eating; nutrients are absorbed and utilized for immediate energy and storage.

• Postabsorptive State: Body relies on internal reserves to maintain blood glucose levels, utilizing stored lipids and amino acids primarily to sustain metabolism during fasting periods.

Nutrition and Dietary Needs

• A balanced diet is essential for homeostasis and includes both macronutrients (proteins, fats, carbohydrates) and micronutrients (vitamins, minerals).

• Malnutrition: Results from nutrient imbalance; a balanced intake from different food groups is recommended (MyPlate) to ensure all essential nutrients are consumed properly.

Metabolic Rate and Thermoregulation

• Metabolic Rate: Defined as the average caloric expenditure, affected by factors such as activity, age, sex, and hormones, playing a crucial role in energy balance.

• Thermoregulation: Mechanisms to maintain body temperature include metabolism regulation, heat exchange processes, and behavioral adjustments, which all work to ensure homeostasis in diverse environments.

Mechanisms of Heat Exchange

• Radiation, Convection, Evaporation, Conduction: These diverse processes allow the body to exchange heat with the environment, vital for thermoregulation.

• The body maintains temperature through responses coordinated by the hypothalamus, integrating signals from different receptors.

Conclusion

• Energy metabolism is a complex interaction of biochemical pathways that encompass how organisms utilize nutrients, regulate energy balance, and maintain homeostasis, highlighting the intricate nature of life processes.