RB

Overview of Cellular Respiration and Glycolysis

Cellular Respiration and Metabolism

  • Overview

    • Cellular respiration is a metabolic process that uses food as fuel along with oxygen.

    • The byproducts of this process are carbon dioxide, water, and energy.

    • Energy produced is vital for various bodily functions, including storage, growth, and repair.

  • Importance of Oxygen

    • Oxygen plays a critical role in burning biomolecules such as proteins, carbohydrates, and lipids for energy.

    • This process supports bodily functions, emphasizing that energy is required for life-sustaining processes.

Energy Transfer in Biological Systems

  • Energy Sources

    • Energy enters the system primarily as light from the sun.

    • Plants convert sunlight into chemical energy stored in carbohydrates.

    • The process also involves the release of carbon dioxide and water into the atmosphere.

    • According to the laws of thermodynamics, energy can neither be created nor destroyed; it only changes forms.

Thermodynamics in Biochemistry

  • Enthalpy (ΔH)

    • Enthalpy refers to the total heat content of a system.

    • Exothermic Reactions:

      • ΔH is negative, meaning heat is released.

    • Endothermic Reactions:

      • ΔH is positive, meaning heat is absorbed.

    • The concept that cold is the absence of heat is clarified in terms of heat removal from a system.

  • Entropy (ΔS)

    • Entropy measures disorder or randomness in a system.

    • Systems tend to prefer states of higher entropy, indicating that increased disorder is favorable (ΔS positive).

    • Common transformation examples include phase changes from solid to liquid to gas, which signify increased entropy.

    • A negative ΔS indicates a decrease in entropy, suggesting a movement towards order, which is typically unfavorable.

Free Energy and Spontaneous Reactions

  • Gibbs Free Energy (ΔG)

    • Combines both ΔH and ΔS to assess spontaneity of a reaction:

    • ΔG negative indicates a spontaneous reaction (energy released).

    • ΔG positive indicates a non-spontaneous reaction (energy absorbed).

    • Terms to Remember:

    • Exergonic: Energy releasing, ΔG negative.

    • Endergonic: Energy absorbing, ΔG positive.

Metabolism

  • Definition

    • Metabolism encompasses all biochemical reactions in living cells, including those that absorb or release energy.

  • Types of Reactions

    • Anabolic Reactions: Build complex molecules, requiring energy.

    • Catabolic Reactions: Breakdown complex molecules, releasing energy.

    • Together, these processes define the organism's metabolic pathways.

Glycolysis

  • Introduction

    • Glycolysis is the primary pathway to convert glucose into energy.

    • It occurs in the cytosol of all cells and is a ten-step process resulting in the production of pyruvate and ATP.

  • Importance of Glucose

    • The human body prefers glucose as its main energy source for critical functions, especially for the brain, muscles, and red blood cells.

Process of Glycolysis

  • Phases of Glycolysis

    • Investment Phase:

    • Uses 2 ATP to phosphorylate glucose, leading to the production of fructose-1,6-bisphosphate.

    • Payout Phase:

    • Produces 4 ATP from ADP, resulting in a net gain of 2 ATP and 2 pyruvate molecules for every glucose molecule.

  • Key Enzymes and Steps

    1. Hexokinase: Phosphorylates glucose to form glucose-6-phosphate.

    2. Conversion to Fructose: Glucose is converted into fructose-6-phosphate to allow further phosphorylation.

    3. Energy Breakthrough: Subsequent steps involve the oxidation of intermediates leading to NADH formation, which will be utilized in the electron transport chain.

Yield of Glycolysis

  • Final Products:

    • Glycolysis results in 2 pyruvate (next fate depends on oxygen availability) and a net gain of 2 ATP.

    • The pathway emphasizes that excess glucose can lead to fat storage if not utilized for energy.

Fate of Pyruvate

  • Aerobic Conditions:

    • Pyruvate is converted into acetyl-CoA when oxygen is abundant, entering the citric acid cycle.

  • Anaerobic Conditions:

    • Pyruvate is converted into lactate in human muscle cells or ethanol in yeast through fermentation.

Lactic Acid Fermentation

  • Important in muscle exercise; buildup causes fatigue, signaling the need for rest.

Fermentation Process

  • Definition: Metabolic process that occurs in the absence of oxygen.

    • Converts pyruvate into lactate or ethanol, retaining energy from glycolysis when oxygen levels are low.

Importance of Oxygen in ATP Production

  • Oxygen is crucial for efficient ATP production through aerobic respiration processes including the citric acid cycle and electron transport chain, highlighting its essential role for sustained cellular energy needs.

Conclusion

  • The understanding of cellular respiration, glycolysis, and energy transfer mechanisms through metabolism is vital in deciphering biological systems and human physiology.