Metabolism and Nutrients Study Guide

Metabolism

Metabolism encompasses all chemical reactions within the body essential for maintaining life.

• Catabolism: Breaking down molecules to release energy (e.g., glucose breakdown during cellular respiration).

• Anabolism: Building larger molecules from smaller ones (e.g., protein synthesis from amino acids).

ATP: The Energy Currency

Adenosine triphosphate (ATP) is the primary energy carrier in cells. Energy is stored in high-energy phosphate bonds and released when ATP is converted to ADP.

Major Metabolic Pathways

Carbohydrate Metabolism

• Glycolysis: Occurs in the cytoplasm; glucose is broken down into pyruvate, yielding 2 ATP.

• Krebs Cycle (Citric Acid Cycle): Occurs in mitochondria; processes pyruvate and generates electron carriers (NADH, FADH2).

• Electron Transport Chain: Occurs in the mitochondrial membrane; produces approximately 32 ATP using oxygen.

Lipid Metabolism

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

• Beta-oxidation: Breaks down fatty acids in the mitochondria to generate acetyl-CoA for the Krebs cycle.

• Lipogenesis: Synthesis of fat from excess glucose or amino acids.

Protein Metabolism

• Amino acids are deaminated (amino group removed), and the remaining carbon skeleton enters the Krebs cycle.

• Excess proteins can be converted into glucose or fat.

Nutrients

Macronutrients

1. Carbohydrates: Primary energy source; stored as glycogen in the liver and muscles.

2. Proteins: Used for building tissues, enzymes, and hormones; can be used for energy.

3. Lipids: Energy storage, insulation, and hormone synthesis.

Micronutrients

• Vitamins: Organic compounds that help enzymes function as coenzymes.

  • Fat-soluble: A, D, E, K

  • Water-soluble: B-complex, C

• Minerals: Inorganic nutrients needed for various body functions (e.g., calcium for bones, iron for hemoglobin).

Water

Water is essential for temperature regulation, chemical reactions, and the transport of substances.

Hormonal Regulation of Metabolism

• Insulin: Lowers blood glucose by promoting glucose uptake and storage.

• Glucagon: Raises blood glucose by promoting glycogen breakdown and gluconeogenesis.

• Thyroid hormones: Increase basal metabolic rate.

Macronutrients

Macronutrients include carbohydrates, proteins, and lipids, which are required in large amounts to provide energy and support body functions.

• Carbohydrates – broken down into monosaccharides (mainly glucose).

  - Digestion begins in the mouth with salivary amylase, continues in the small intestine with pancreatic amylase.

  - Absorption occurs in the small intestine (mostly jejunum) via active transport into blood capillaries.

• Proteins – broken down into amino acids.

  - Digestion begins in the stomach (pepsin), continues in the small intestine with pancreatic proteases (trypsin, chymotrypsin).

  - Absorbed in the small intestine (duodenum and jejunum) via active transport into blood.

• Lipids – broken down into fatty acids and monoglycerides.

  - Emulsified by bile salts in the small intestine.

  - Pancreatic lipase breaks triglycerides into absorbable units.

  - Absorbed in the small intestine (mostly ileum) into lymphatic vessels via micelles and chylomicrons.

Micronutrients

Micronutrients include vitamins and minerals, which are required in smaller amounts but are essential for many physiological functions.

• Fat-soluble vitamins (A, D, E, K) – absorbed in the small intestine with dietary fats; stored in body fat.

• Water-soluble vitamins (B-complex, C) – absorbed directly into the bloodstream in the small intestine.

• Major minerals (e.g., calcium, sodium, potassium) – absorbed in the small intestine; calcium absorption is enhanced by vitamin D.

• Trace minerals (e.g., iron, zinc, iodine) – absorbed in the small intestine in smaller quantities.