Metabolism Lecture Notes

Metabolism Overview

Definition of Metabolism

  • Metabolism: The sum total of all chemical reactions in the body, which includes both anabolic (building) and catabolic (breaking down) reactions.
    • Anabolism: Refers to the processes that build complex molecules from simpler ones (e.g., synthesis of proteins from amino acids).
    • Catabolism: Refers to the processes that break down complex molecules into simpler ones, often releasing energy (e.g., breaking down glucose to extract energy).

Relationship between Anabolism and Catabolism

  • Metabolism is a combination of anabolism and catabolism. These processes are interconnected; catabolic processes provide the energy and building blocks for anabolic processes.
    • Energy conversion: Catabolic reactions generate ATP, which is then utilized in anabolic reactions.

Catabolic Pathways

Overview

  • Catabolic pathways serve as fuel sources by breaking down nutrient molecules into smaller units, releasing energy in the form of ATP.
  • Nutrient molecules are digested into monomers: glucose, fatty acids, and amino acids.
  • The macromolecules ingested are broken down to harness energy and liberate ATP.

Key Catabolic Processes

  1. Cellular Respiration: A process by which cells convert glucose into ATP.
    • Overall Reaction:
      C6H{12}O6 + 6O2 -> 6H2O + 6CO2 + 38ATP + heat
    • Includes the following stages:
      • Glycolysis: The breakdown of glucose into pyruvate, yielding 2 ATP and 2 NADH.
      • Citric Acid Cycle: Further breaks down pyruvate to acetyl-CoA, producing additional NADH and ATP.
      • Electron Transport Chain (ETC): NADH and FADH2 donate electrons to produce ATP, water, and heat through oxidative phosphorylation.

Anabolic Pathways

Overview

  • Anabolic pathways utilize ATP and other energy-rich molecules to build larger, more complex molecules.
  • These processes convert nutrients into forms that can be stored for later use or utilized for growth and repair.

Key Anabolic Processes

  1. Glycogenesis: The process of converting glucose into glycogen for storage in the liver and muscles.
  2. Lipogenesis: The synthesis of triglycerides from fatty acids and glycerol, primarily for energy storage.
  3. Protein Synthesis: Building proteins from amino acids, crucial for cellular structure and function.
  4. Gluconeogenesis: The synthesis of glucose from non-carbohydrate sources.
  5. Key metabolic states:
    • Absorptive State: Dominated by anabolic processes, occurs immediately after eating when glucose levels are high.
    • Post-Absorptive State: Dominated by catabolic processes, typically occurring when the body is fasting of 4 hours or more after a meal.

Hormonal Control of Metabolism

Overview

  • Hormones play a significant role in regulating metabolic pathways and energy levels.
  • The primary hormones involved are insulin and glucagon.

Hormonal Effects

  1. Insulin:

    • Secreted by the pancreas in response to high blood glucose levels during the absorptive state.
    • Promotes anabolism: Stimulates glycogenesis, lipogenesis, and protein synthesis, facilitating nutrient storage.

  2. Glucagon:

    • Secreted by the pancreas during the post-absorptive state when blood glucose levels drop.
    • Promotes catabolism: Stimulates glycogenolysis (breakdown of glycogen) and gluconeogenesis, facilitating the release of glucose into the bloodstream.

Nutritional Sources and Their Metabolism

Macronutrients

  1. Carbohydrates: Main source of energy for cells (mainly glucose).
  2. Fats (Lipids): Serve as long-term energy storage (triglycerides).
  3. Proteins: Provide amino acids for various cellular functions, particularly in tissue repair and synthesis.

Interconnections and Conversions

  • Overview: Excess carbohydrates, fats, and proteins can be converted into various forms through metabolic pathways, affecting energy balance and storage.
  • Metabolic Pathway Flow:
    • Nutrients are converted and stored as:
    • Glycogen
    • Triglycerides
    • Proteins
  • Lipogenesis: Converts excess triglycerides into body fat, prompted by excess caloric intake.

Nutrient Levels and Their Regulation

Blood Sugar Levels

  • Blood glucose levels fluctuate throughout the day based on food intake and metabolic states.
  • Events after a meal:
    • Rapid increase in blood glucose and insulin levels.
  • Events in fasting:
    • Decrease in blood glucose level; glucagon is released, leading to catabolic processes.

Health Implications of Sugars

  • Notable concerns regarding added sugars (e.g., high-fructose corn syrup) include:
    • It can lead to metabolic syndrome, characterized by:
    • Abdominal fat
    • Hypertension (HTN)
    • Insulin resistance and high cholesterol
    • Increased risk of diabetes type II and fatty liver disease.
  • Fatty acids, amino acids, and glucose play crucial roles in providing energy to neurons and various cells during different metabolic states.