Metabolism and Energy Production

Nutrients

• Definition: Essential substances needed for cells to generate energy in the form of ATP.

• Functions: Support cell growth, division, contraction, secretion, etc.

Metabolism

• Definition: All chemical reactions in the body.

• Divisions:

  • Catabolism: Breakdown of organic molecules.

  • Anabolism: Synthesis of new organic molecules.

Interstitial Fluid and Cell Functions

• Key Functions:

  • Maintenance and repairs.

  • Growth.

  • Secretion.

  • Stored nutrient reserves.

Nutrient Pool

• Components: Organic molecules including amino acids, lipids, and simple sugars.

• Anabolic Activities: Require amino acids, some lipids, and few carbohydrates.

• Catabolic Reactions:

  • Break down carbohydrates first, followed by lipids, and rarely amino acids.

Types of Metabolism

• Anaerobic Catabolism: Limited to small ATP production under unusual conditions.

• Aerobic Metabolism (Cellular Respiration): Occurs in mitochondria and accounts for 40% of the energy produced.

Energy Expenses in ATP Usage

• Other ATP Expenses: Includes locomotion, contraction, intracellular transport, cytokinesis, endocytosis, and exocytosis.

Overview of Carbohydrate Metabolism

• Cellular Respiration Equation: $C_6H_{12}O_6 + 6O_2 ightarrow 6CO_2 + 6H_2O + 36 ATP$

  • Aerobic: Requires oxygen and occurs in mitochondria.

  • Anaerobic: Does not require oxygen.

Redox Reactions

• Definitions:

  • Oxidation: Remove electrons, making the particle more positive (e.g., $Na^+$).

  • Reduction: Add electrons, making the particle less positive (e.g., $Cl^-$).

• Redox Reactions: Electron transfer between materials.

Cellular Respiration Overview

• Processes:

  • Glucose is oxidized.

  • Oxygen is reduced.

• Detailed Equation:
  $C_6H_{12}O_6 + 6 O_2 <br>ightarrow 6 CO_2 + 6 H_2O + 36 ATP + ext{heat}$

Glycolysis

• Definition: Breakdown of glucose into two molecules of pyruvate ($CH_3—CO—COOH$).

• Process:

  • Enters mitochondria to harvest high-energy electrons.

  • NAD+ conversion: $NAD^+ + 2 e^- <br>ightarrow NADH$.

  • Initial ATP investment: 2 ATP yields 4 ATP for a net gain of 2 ATP.

Steps in Glycolysis

1. Glucose is phosphorylated twice (costs 2 ATP).

2. The six-carbon chain splits into two three-carbon molecules.

3. Harvest energy and produce 2 ATP and NADH.

Mitochondrial Structure

• Composition:

  • Surrounded by two membranes:

  • Outer Membrane: Permeable to pyruvate.

  • Inner Membrane: Uses carrier proteins to transport pyruvate into the mitochondrial matrix.

• Key Cycles: Citric Acid Cycle and Oxidative Phosphorylation.

The Citric Acid Cycle (Krebs Cycle)

• Pyruvate Conversion: To acetyl-CoA (2 carbon sugar).

• Energy Harvesting: Produces 2 ATP from GTP, 8 NADH, 2 FADH2, and releases six CO2.

• Electron Transport System: NADH and FADH2 feed into it.

Electrons Carriers in Cellular Respiration

• Types:

  • NAD+ (Nicotinamide adenine dinucleotide) + 2 electrons = $NADH$.

  • FAD (Flavin adenine dinucleotide) + 2 electrons = $FADH_2$.

Oxidative Phosphorylation

• Electron Transport System (ETS):

  • Embedded in the inner mitochondrial membrane.

  • Provides 95% of all cellular energy.

  • Series of protein-pigment cytochromes facilitate stepwise electron energy release.

Electron Transport and ATP Formation

• Key Process: Protons from NADH and FADH2 are split, leading to a proton gradient and ATP synthesis through ATP synthase, a process termed "chemiosmosis".

Summary of Energy Yield from Carbohydrates

• Energy Outputs:

  • Glycolysis: 2 ATP

  • Citric Acid Cycle: 2 ATP

  • Electron Transport System: 32 ATP

• Total ATP from one glucose molecule: 36 ATP (primarily produced in mitochondria).

Mitochondrial Diseases

• Symptoms may include:

  • Poor growth

  • Developmental delay

  • Muscle weakness

  • Gastrointestinal disorders

  • Neurological issues (e.g., seizures)

  • Increased infection susceptibility.

Gluconeogenesis

• Definition: The synthesis of "new" glucose from non-carbohydrate sources.

• Intermediates Used: Lactate, glycerol, and specific amino acids with different enzymes than those for glycolysis.

Alternate Catabolic Pathways

• Scenarios without Oxygen:

  • Fermentation occurs; otherwise cells will die.

• Without Glucose: Cells can utilize lipids and proteins for energy, while nucleic acids are rarely used.

Lipid Catabolism (Fat Metabolism)

• Definition: Lipolysis, the hydrolysis of triglycerides into components like glycerol and fatty acids.

• Energy Yield: 18-carbon fatty acid can yield 144 ATP via beta-oxidation.

Beta-Oxidation Process

• Occurs in mitochondria, breaking down fatty acids in two-carbon units.

• Produces FADH2, NADH, and Acetyl-CoA.

Diabetes Type I Warning Signs

• Presence of ketones in blood/breath due to insulin deficiency, high blood sugar levels, with blood sugars often exceeding 250 mg/dl.

• Risk of diabetic ketoacidosis and pH imbalance.

Lipids and Energy Production

• Storage: Lipids stored in fat droplets; present a challenge for water-soluble enzymes.

• Energy Access:

  • Skeletal muscle fibers primarily access glucose for quick energy and fatty acids during rest.

Lipid Synthesis (Lipogenesis)

• Sources: Glycerol derived from glycolysis products and acetyl-CoA used to build steroids and fatty acids.

• Essential Fatty Acids: Must be obtained from diet, including omega-3 and omega-6 fatty acids.

Lipoproteins and Lipid Transport

• Composition: Contain triglycerides, cholesterol, wrapped in phospholipids and proteins.

• Types:

  • Chylomicrons: Largest, transport fat from intestines to body.

  • Low-Density Lipoproteins (LDLs): Carry cholesterol from liver to tissues (often termed as “bad cholesterol”).

  • High-Density Lipoproteins (HDLs): Transport cholesterol from tissues back to liver (termed as “good cholesterol”).

Cholesterol Transport Mechanism

• Hyperlipidemia Consequences: Cholesterol re-entering bloodstream from peripheral tissues to be transported back to the liver by HDLs, sorted for reuse or excretion with bile.

Questions

• Open floor for questions before proceeding to discuss amino acids.