Concept of Bioenergetics | Zoology Optional Notes for UPSC PDF Download

Definition of Bioenergetics

• Bioenergetics is the study of energy transformation in living organisms.
• The primary goal is to elucidate how living organisms acquire and transform energy for biological work, emphasizing the importance of metabolic pathways.

Energy Transformation in Living Organisms

• In living organisms, energy is exchanged through the breaking and making of chemical bonds.
• Weak bonds are broken, and stronger bonds are formed, releasing usable energy.
• Adenosine triphosphate (ATP) acts as the main "energy currency," synthesized and utilized in metabolic processes.

Energy Charge in Cells

• The ratio of ATP to ADP concentrations in a cell is known as the "energy charge."
• It serves as a cellular indicator, guiding information about energy availability and needs.

Types of Bioenergetics Reactions

1. Exergonic Reactions

• Exergonic reactions release energy spontaneously, significant in catabolic reactions.
• Weak bonds are broken, forming stronger bonds, releasing free energy (ΔG < 0).

2. Endergonic Reactions

• Endergonic reactions require an input of free energy, common in anabolic processes.
• The release of free energy is non-spontaneous (ΔG > 0).

3. Activation Energy

• Activation energy is the minimum energy required to initiate a chemical reaction.

Examples of Major Bioenergetics Processes

Glycolysis

• Breaks down glucose into pyruvate, producing ATP and NADH.

Gluconeogenesis

• Synthesizes glucose from biomolecules when the cell's energy charge is low.

Citric Acid Cycle

• In cellular respiration, produces metabolites and conserves energy in FADH2 and NADH.

Ketosis

• Metabolic process using ketone bodies for energy, often during low glucose levels.

Oxidative Phosphorylation and Electron Transport Chain

• Utilizes reducing equivalents for ATP synthesis in mitochondrial membrane complexes.

Photosynthesis

• Converts solar energy into glucose in plants' chloroplasts.

Bioenergetics Relationship Between Free Energy, Enthalpy & Entropy

• Living cells harvest and channel energy for biological work.
• 1st Law: Energy of the universe remains constant.
• 2nd Law: Spontaneous processes increase the entropy of the universe.

Key State Functions

• Gibbs Free Energy (G): Total energy capable of doing work.

  • ∆G < 0: Spontaneous (exergonic)
  • ∆G > 0: Nonspontaneous (endergonic)
  • ∆G = 0: Equilibrium

• Enthalpy (H): Heat content under constant pressure.

  • ∆H < 0: Exothermic
  • ∆H > 0: Endothermic

• Entropy (S): Quantitative expression of system disorder.

  • ∆S > 0: Increased disorder
  • ∆S < 0: Decreased disorder

• The relationship is described by ∆G = ∆H − T∆S, where T is the temperature in Kelvin.

Understanding these principles is essential for unraveling the complex energy dynamics within living organisms.

High Energy Phosphates: The Cellular Energy Currency

• High-energy phosphates serve as the energy currency within cells.
• Three major sources participate in energy conservation or capture.

1. Oxidative Phosphorylation (OXPHOS)

• Definition: A metabolic pathway occurring in mitochondria where enzymes oxidize nutrients, releasing energy for ATP production.
• Importance: Highly efficient for energy release compared to alternative processes.
• Key Molecules: NADH and FADH2, products of glycolysis and citric-acid cycle, serve as reducing agents.
• Significance: Used in oxidation-reduction reactions, contributing to energy capture.

2. Glycolysis

• Process: Extracts energy from glucose, producing ATP and NADH.
• Outcome: Yields pyruvate as the end product, further used in various metabolic pathways.
• ATP Formation: Occurs through reactions in the aerobic phase of glycolysis.

3. Tricarboxylic Acid (TCA) Cycle

• Definition: A series of reactions in cellular respiration releasing energy from acetyl-CoA.
• Outcome: Produces carbon dioxide and chemical energy (ATP) from the oxidation of substrates.
• ATP Generation: Oxidation of substrates through NADH and FADH2 in the electron transport chain.
• Intermediates: Result as two molecules from one molecule of glucose in glycolysis.

Energy Shuttles: NADH and FADH2

• NADH: An energy shuttle delivering high-energy electrons to the electron transport chain.
  • When oxidized, termed NAD+.
• FADH2: Another shuttle delivering electrons, ultimately contributing to ATP production.
  • The oxidized form is FAD.

High Energy Molecules

• ATP: Primary energy currency used immediately in cellular processes.
• GTP: Similar to ATP, easily convertible to ATP within the cell.

Adenosine Triphosphate (ATP)

• Definition: ATP, a multifunctional nucleotide, acts as a coenzyme and intracellular energy transfer currency.
• Production: Via photophosphorylation and cellular respiration.
• Structure: Adenine base attached to ribose sugar with three phosphate groups.
• Functions:
  1. Transport: Facilitates the movement of organic substances through cell membranes.
  2. Synthesis: Involved in the production of proteins and cholesterol.
  3. Energy Supply: Powers mechanical work like muscle contraction.
• Energy Release: Hydrolysis of ATP releases energy (ΔG = −30.5 kJ/mol).
• Regulation: Cellular conditions maintain ΔG at approximately −57 kJ/mol.

Cyclic Adenosine Monophosphate (cAMP)

• Definition: cAMP, derived from ATP, acts as a second messenger in intracellular signal transduction.
• Synthesis: Formed by adenylyl cyclase, activated by Gs-protein-coupled receptors.
• Decomposition: Catalyzed by phosphodiesterase.
• Function: Regulates protein kinase activation, influencing biochemical processes.
  • Involves in the effects of hormones like glucagon and adrenaline.

Guanosine Triphosphate (GTP): A Versatile Nucleotide

• Definition: GTP, a purine nucleoside triphosphate, serves roles in RNA/DNA synthesis and energy transfer.
• Energy Transfer: Involved in cellular energy transfer, equivalent to ATP generation.
• Genetic Translation: Supplies energy for binding new amino-bound tRNA during translation.
• Mitochondrial Function: Vital in translocating proteins into the mitochondrial matrix.

Cyclic Guanosine Monophosphate (cGMP)

• Definition: cGMP, derived from GTP, acts as a cyclic nucleotide second messenger.
• Synthesis: Catalyzed by guanylate cyclase from GTP.
• Functions:
  • Regulates ion channel conductance, glycogenolysis, and apoptosis.
  • Induces vasodilation, increasing blood flow.
  • Acts as a secondary messenger in phototransduction.

Understanding these compounds is crucial for comprehending cellular processes and the intricate balance of energy within living organisms.