Metabolism Chapter Lecture

Key Concepts

• Metabolism: Entirety of chemical reactions happening in the body post-nutrient absorption.
• ATP Production: Focus is on how ATP is produced using various nutrients like carbs, fats, and proteins.

Carbohydrates

• Sources: Mostly from plants; includes glucose, fructose, galactose; lactose from dairy.
• Forms: Monosaccharides (e.g., glucose), disaccharides (e.g., sucrose, maltose), polysaccharides (e.g., starches, glycogen).
• Functions:
  • Used for ATP production
  • Stored as glycogen in liver and muscles
  • Excess converted into fats (triglycerides)
• Other Uses: Carbohydrates needed for DNA, RNA, ATP, and glycoproteins.

Lipids

• Types: Triglycerides (saturated, unsaturated, trans fats), cholesterol, phospholipids.
• Sources: Animal fats, plant oils; cholesterol from animal products but also synthesized by the body.
• Functions:
  • ATP production and storage
  • Formation of hormones and cell membranes
  • Components in bile and signaling molecules
• Health Impact: Saturated and trans fats worse for health; unsaturated fats better.

Proteins

• Essential Amino Acids: Must be obtained from diet (e.g., histidine, leucine, lysine).
• Sources: Complete proteins (meat, fish, eggs), incomplete proteins (require combining different sources).
• Functions:
  • Structural roles (collagen, muscle)
  • Enzymes, hormones, antibodies
  • Transport mechanisms (hemoglobin, ion channels)

Vitamins

• Definition: Organic molecules required in the diet as the body cannot synthesize them.
• Types:
  • Fat-Soluble (A, D, E, K): Stored in fat, can become toxic if in excess.
  • Water-Soluble (B complex, C): Not stored, excess excreted in urine.
• Functions: Act as coenzymes for various biochemical reactions.

Minerals

• Definition: Inorganic compounds needed for physiological functions (e.g., sodium, calcium).
• Types:
  • Major Minerals: Needed in amounts >= 100 mg/day.
  • Trace Minerals: Needed in smaller amounts.
• Functions: Maintain homeostasis, bone health, nerve and muscle function, etc.

Metabolism Overview

• Catabolic Reactions: Break down molecules, release energy.
• Anabolic Reactions: Build up molecules, require energy.
• ATP: Main energy currency in the body, generated through various metabolic pathways.

ATP Production

1. Glycolysis:

   • Occurs in cytoplasm, converts glucose to pyruvate.
   • Net gain: 2 ATP, 2 NADH, 2 pyruvate.
   • Steps:
     • Glucose phosphorylated using 2 ATPs.
     • Converted to fructose-1,6-bisphosphate, then split into 2 molecules of G3P.
     • Produces 4 ATP (net gain 2) and 2 NADH.

2. Anaerobic Respiration (No Oxygen):

   • Pyruvate converted to lactate.
   • Allows regeneration of NAD+ for glycolysis to continue.
   • Yields 2 ATP.

3. Aerobic Respiration (Requires Oxygen):

   • Pyruvate enters mitochondria, converted to Acetyl-CoA.
   • Enter Citric Acid Cycle, producing ATP, NADH, FADH2, and CO2.
   • Electron Transport Chain: Major ATP production (28 ATP).
   • Total ATP per glucose: ~32 ATP.

Citric Acid Cycle (Kreb's Cycle)

• Process:
  • Converts Acetyl-CoA to CO2, transferring energy to NADH and FADH2.
  • Each cycle generates 1 ATP, 3 NADH, and 1 FADH2.
  • Two cycles per glucose molecule.
• Importance: Provides substrates for Electron Transport Chain, majority of cellular ATP production.

Electron Transport Chain

• Function: Uses NADH and FADH2 to generate ATP through oxidative phosphorylation.
• Oxygen Role: Final electron acceptor, forms water.
• Yield: ~28 ATP from a single glucose molecule.

Summary

• Understanding of metabolism involves the comprehension of how macronutrients are broken down and utilized at the cellular level for energy production. The efficiency and efficacy of these metabolic pathways are vital for maintaining bodily functions and overall health.