Overview of Cellular Energy and Metabolism

• Importance of Energy

  • ATP (Adenosine Triphosphate) is the most critical form of chemical energy in cells.

  • ATP is utilized for various cellular processes such as movement (e.g., flagella) and transporting molecules.

• Electrons in Metabolism

  • Metabolism involves managing electrons to produce chemical energy.

  • Electron management is critical for generating ATP, with a focus on two methods:

  1. Functional Group Transfer

     • Involves the transfer of functional groups (e.g., phosphate, methyl, amino groups) between substrates.

     • Common example: ATP donating a phosphate group to another molecule during glycolysis.

     • Example Process:

       • Reaction: Glucose + ATP → Glucose-6-Phosphate + ADP.

       • ATP possesses three phosphates; the energy released from cleaving the last phosphate is used in reactions.

  2. Redox Reactions

     • Comprising oxidation (loss of electrons) and reduction (gain of electrons).

     • Oxidation cannot occur without a simultaneous reduction of another substrate.

     • Controlled series of reactions to release energy gradually to avoid large heat release.

     • Transfers energy to the electron transport chain for ATP production.

• Key Coenzymes in Energy Management

  • NAD (Nicotinamide Adenine Dinucleotide) and FAD (Flavin Adenine Dinucleotide) are crucial coenzymes.

  • NADH (reduced form): picks up electrons to store energy.

  • FADH2 (reduced form): carries electrons to the electron transport chain after reduction.

  • Example:

    • NAD + e- + H → NADH (stores energy).

ATP Generation Methods

Categories of ATP Production

• Organisms generate ATP in three main ways:

  1. Substrate Level Phosphorylation

  • Occurs during glycolysis and Krebs cycle; simplest and oldest method.

  • Involves direct transfer of a phosphate group to ADP to form ATP.

  • Example: Reaction during glycolysis producing ATP from phosphoenolpyruvate.

  1. Oxidative Phosphorylation

  • Involves the electron transport chain and chemiosmosis.

  • The majority of ATP is generated through this method.

  1. Photophosphorylation

  • Associated with photosynthesis; converts light energy to chemical energy in plants.

Details of ATP Production Methods

• Substrate Level Phosphorylation

  • Takes place in both aerobic and anaerobic respiration.

  • Example Process:

    • ADP + Phosphate → ATP (phosphate comes from another substrate).

• Oxidative Phosphorylation

  • Operates in the electron transport chain, where NADH and FADH2 are oxidized to generate ATP.

  • Involves pumping protons to create a gradient, driving ATP synthesis via ATP synthase (chemiosmosis).

Cellular Respiration Process

• Overview of Cellular Respiration

  • Two main methods for glucose breakdown:

  1. Aerobic Cellular Respiration: Requires oxygen; includes glycolysis, Krebs cycle, and electron transport chain.

  2. Fermentation: Anaerobic process.

Glycolysis

• Definition: 10-step biochemical pathway breaking glucose into pyruvate.

• Overall Reaction:

  • Glucose (C6H12O6) + 2 ATP → 2 Pyruvate (C3H4O3) + 4 ATP (NET 2 ATP) + 2 NADH.

• Key Points:

  • Occurs in the cytoplasm.

  • Anaerobic; does not require oxygen.

  • Products include: 2 ATP (net), 2 pyruvate, 2 NADH.

Krebs Cycle (Citric Acid Cycle)

• Definition: A cyclic process that continues the breakdown of glucose after glycolysis.

• Process: Each acetyl CoA that enters results in:

  • Production of 2 CO2, 3 NADH, 1 FADH2, 1 ATP.

• Overall Reaction:

  • Each glucose yields 2 acetyl CoA (thus undergoing the cycle twice).

Electron Transport Chain

• Functionality: Located in the inner mitochondrial membrane of eukaryotic cells (plasma membrane in prokaryotes).

• Mechanism:

  • NADH and FADH2 donate electrons, creating a proton gradient leading to ATP synthesis.

  • Final electron acceptor is oxygen, forming water.

• Production Rate:

  • 3 ATP per NADH, 2 ATP per FADH2.

Total ATP Yield from Cellular Respiration

• Glycolysis: 2 ATP (net).

• Krebs Cycle: 2 ATP.

• Electron Transport Chain: 34 ATP.

• Total Potential: 38 ATP per glucose under ideal conditions.

• Key Summary Points:

  • Glucose is oxidized to produce carbon dioxide, water, and ATP.

  • Each glucose molecule generates an estimated maximum of 38 ATP through combined processes.

Other Metabolic Pathways

• Pentose Phosphate Pathway: Functions alongside glycolysis; generates ribose for nucleic acid synthesis and carries intermediates.

• Entner-Doudoroff Pathway: Pathway used by certain bacteria; yields less energy compared to glycolysis.

  • Produces fewer ATP and intermediates that can integrate into glycolysis.

Summary and Exam Preparation

• Focus on key processes: Glycolysis, Krebs Cycle, Electron Transport Chain.

• Understand ATP production locations, amounts generated, and the differing pathways' roles in metabolism.

• Prepare a study guide to consolidate knowledge of processes, reactions, and their outcomes for exam readiness.