PLTL 10/10

Overview of Metabolism Principles

Metabolism: The biochemical processes that occur within a living organism to maintain life.

Energy Requirement: Synthesis reactions require energy to form complex molecules from simpler ones.
**Thermodynamics:
- Endergonic Reaction:** These reactions are characterized by a positive change in Gibbs free energy (ΔG > 0).
- Entropy Considerations: These reactions result in a decrease in entropy within the system since they build complex molecules.

Energy Release: Breakdown reactions release energy as complex molecules are broken down into simpler substances.
**Thermodynamics:
- Exergonic Reaction:** These reactions are characterized by a negative change in Gibbs free energy (ΔG < 0).
- Entropy Considerations: These reactions result in an increase in entropy in the system as they produce smaller, more disordered molecules.

ATP → ADP + Pi, ΔG = −7.3 Kcal/mol: This equation demonstrates that the hydrolysis of ATP to ADP (adenosine diphosphate) and inorganic phosphate releases energy.
- Meaning of ΔG: The negative value indicates that the reaction is exergonic, which signifies it can perform work.

Definition of High-Energy Bond: High-energy bonds, particularly in ATP, are those that release large amounts of energy upon hydrolysis. Their energy release is due to the repulsion between negatively charged phosphate groups and the stabilization of the products.

ATP and Enzyme Coupling: ATP can couple endergonic (energy-requiring) reactions with exergonic (energy-releasing) reactions through the transfer of energy from ATP hydrolysis. This is important for enabling various cellular processes that require energy, such as biosynthesis, transport, and cellular locomotion.

High-Energy Electrons: Molecules such as NADH and FADH2 carry high-energy electrons which are crucial for energy production in cellular respiration.
- Definition: High-energy electrons are those that have gained energy during biochemical reactions, making them capable of contributing to the production of ATP.

Oxidation: The process in which a molecule loses electrons, often associated with the loss of energy.
Reduction: The process in which a molecule gains electrons, associated with an increase in energy.
- Key Terms: These reactions are often represented by half-equations showing electron transfer.

Diagram Information: Four main phases are involved in cellular respiration:
- Glycolysis: Occurs in the cytoplasm, breaks glucose into two pyruvate molecules.
- Pyruvate Oxidation: Takes place in the mitochondria; converts pyruvate into Acetyl-CoA, generating NADH.
- Krebs Cycle (Citric Acid Cycle): Occurs in the mitochondrial matrix; processes Acetyl-CoA to produce ATP, NADH, FADH2, and CO2.
- Oxidative Phosphorylation: Takes place across the inner mitochondrial membrane; utilizes electrons from NADH and FADH2 to produce ATP via the electron transport chain (ETC).

Glycolysis: Reactants: Glucose, NAD+, ATP; Products: 2 Pyruvate, NADH, ATP (net gain 2 ATP).
- Accomplishment: Energy extraction and conversion of glucose into pyruvate.
Pyruvate Oxidation: Reactants: 2 Pyruvate, NAD+; Products: 2 Acetyl-CoA, NADH, CO2.
- Accomplishment: Conversion of pyruvate into Acetyl-CoA.
Krebs Cycle: Reactants: Acetyl-CoA, NAD+, FAD, ADP; Products: ATP, NADH, FADH2, CO2.
- Accomplishment: Complete oxidation of Acetyl-CoA, energy generation.
Oxidative Phosphorylation: Reactants: NADH, FADH2, O2; Products: ATP, H2O.
- Accomplishment: Production of ATP via electron transport and chemiosmosis.

H+ Ions Pumping Calculation:
- From NADH: The transport of 2 high-energy electrons from one NADH molecule results in pumping approximately 10 H+ ions across the membrane.
- From FADH2: The energy from 2 high-energy electrons carried by one FADH2 typically results in pumping about 6 H+ ions.
ATP Production by ATP Synthase:
- For each NADH: Approximately 2.5 ATP molecules are produced.
- For each FADH2: About 1.5 ATP molecules are produced.

Total ATP Yield Determination: To calculate total ATP yield from one glucose molecule, consider the contribution from glycolysis (2 ATP via substrate-level phosphorylation), Krebs cycle (2 ATP), and oxidative phosphorylation (approximately 28 ATP from 10 NADH and 2 FADH2). This results in a theoretical maximum of about 30-32 ATP per glucose molecule in aerobic conditions.

Oxygen Deprivation and Cellular Respiration: In conditions where there is insufficient oxygen due to intense exercise, cells switch from aerobic respiration to anaerobic respiration, leading to lactate production (lactic acid fermentation).
- Advantage of Process: This allows for short-term ATP production, which supports muscle activity when oxygen levels are low.

Survival Without Water: Discussing gerbils, their ability to survive without drinking water can be attributed to their efficient water conservation strategies, including metabolic water formation from cellular respiration, showcasing adaptations that allow for survival in arid environments.

Region of Highest H+ Concentration: The intermembrane space of the mitochondria, where protons accumulate.
pH Comparison: The pH level in this region is more acidic compared to the more basic environment of the mitochondrial matrix.

Mechanism of Ion Movement: Hydrogen ions (H+) reach the intermembrane space via the action of electron transport chain proteins, which utilize the energy released from electrons.
Energy Requirement for Ion Movement: Moving H+ ions across the membrane requires energy because they are being pumped against a concentration gradient.
Source of Energy: This energy is derived from the redox reactions of the ETC which release energy as electrons are transferred through the chain.

Electron Flow Pathway: Electrons follow a specific pathway through the ETC, beginning from complexes I and II, moving through coenzyme Q (ubiquinone) and cytochrome c, and ending at complex IV. The pathway is determined by the redox potentials of the electron carriers, allowing for controlled energy release.

Final Electron Acceptor: Molecular oxygen (O2) is the final electron acceptor in the electron transport chain.
Final Product: As a result of this process, water (H2O) is formed when oxygen accepts electrons and combines with protons.

Role of ETC in ATP Production: The electron transport chain creates a proton gradient that drives ATP production through ATP synthase, showcasing the interconnectedness of these processes in cellular respiration.