Overview of Metabolism

Key Concepts

• Macronutrients: Carbohydrates, Proteins, Triglycerides (fats)
  • Carbohydrates: Composed of carbons, hydrogens, and oxygens
  • Proteins: Composed of carbons, hydrogens, oxygens, and nitrogen
  • Triglycerides: Composed of carbons, hydrogens, and oxygens

Digestion and Absorption

• Carbohydrates:
  • Broken down by amylase in saliva into glucose
  • Absorbed into the bloodstream (portal system to liver)
• Proteins:
  • Unfolded by hydrochloric acid in the stomach
  • Broken down by pepsin into amino acids
  • Absorbed into the bloodstream (portal system to liver)
• Fats (Triglycerides):
  • Broken down by bile and lipases into glycerol and fatty acids
  • Absorbed into the lymphatic system, eventually reaching the liver

Metabolic Pathways

• Glucose Metabolism:

  • Glycogenesis: Storage of glucose as glycogen
  • Glycogenolysis: Splitting glycogen back into glucose
  • Glycolysis: Conversion of glucose into pyruvate, leading to ATP production

• Krebs Cycle:

  • Also known as the citric acid cycle or tricarboxylic acid cycle
  • Converts pyruvate into acetyl CoA with oxaloacetate
  • Produces NADH and FADH2 for the electron transport chain

• Electron Transport Chain:

  • Series of proteins in the mitochondrial membrane
  • Transfers electrons and pumps hydrogen ions to produce ATP
  • Requires oxygen (oxidative phosphorylation)

Alternative Energy Sources

• Amino Acids:
  • Can't be stored; excess is deaminated and excreted as urea
  • Some enter glycolysis or the Krebs cycle
• Glycerol and Fatty Acids:
  • Can enter glycolysis or the Krebs cycle

Ketone Bodies

• Ketogenesis:
  • Occurs when glucose is absent
  • Acetyl CoA accumulates and forms ketones
  • Ketones used by the brain can convert back to acetyl CoA
• Ketolysis:
  • Conversion of ketones back into acetyl CoA in the brain

Gluconeogenesis

• Production of glucose from non-carbohydrate sources
  • Amino acids and glycerol contribute to glucose production

Lipid Metabolism

• Lipogenesis: Formation of triglycerides for storage
• Lipolysis: Breakdown of triglycerides into glycerol and fatty acids

Additional Notes

• Lactate Production:
  • Under anaerobic conditions, pyruvate converts to lactate
  • Lactate can buffer hydrogen ions, preventing acidosis

This overview covers the essential biochemical pathways involved in metabolism, highlighting the integration and regulation of energy sources within the body.