In-Depth Notes on Metabolism and Energy Transfer

6.1 ENERGY AND METABOLISM

• Bioenergetics: Study of energy flow through living systems.
• Metabolism: All chemical reactions in a cell or organism.
  • Metabolic pathway: Sequence of biochemical reactions converting substrates into products, e.g., photosynthesis produces glucose from CO₂ and H₂O.

METABOLIC PATHWAYS

• Two Types of Metabolic Reactions:
  • Anabolic Reactions: Require energy to synthesize larger molecules.
  • Catabolic Reactions: Release energy by breaking down larger molecules into smaller ones.

EVOLUTION OF METABOLIC PATHWAYS

• Shared metabolic pathways among different life forms suggest a common ancestry.
• Organisms evolved specialized enzymes for adaptation.

ANABOLIC AND CATABOLIC EXAMPLES

• Photosynthesis is an example of metabolic pathways involving anabolic and catabolic processes.

DISCUSSION QUESTION

• Is photosynthesis anabolic or catabolic?
  • Photosynthesis is anabolic as it builds glucose using energy from sunlight.

TYPES OF ENERGY

• Energy: Ability to do work, classified as:
  • Kinetic Energy: Energy of moving objects.
  • Potential Energy: Stored energy, e.g., energy in chemical bonds.

EXAMPLES OF ENERGY IN CELLS

• Chemical/Electrochemical Gradients: Example of potential energy across cell membranes.
• Chemical Energy: Energy stored in chemical bonds, transformed into kinetic energy.

POTENTIAL ENERGY TRANSFORMATION

• Example: Potential energy in gasoline converted to kinetic energy in cars.

GIBB'S FREE ENERGY

• Gibbs Free Energy (G): Energy available to do work in a reaction.
  • Change in G after a reaction: $ext{ΔG} = ext{ΔH} - T ext{ΔS}$
  • $ext{ΔH}$: Change in total energy.
  • $T$: Temperature (in K).
  • $ext{ΔS}$: Change in entropy (energy lost).

FREE ENERGY AND REACTION CLASSIFICATION

• If ext{ΔG} < 0, the reaction is exergonic (spontaneous, releases energy).
• If ext{ΔG} > 0, the reaction is endergonic (requires energy input).

ACTIVATION ENERGY

• Energy required to start a reaction, often in the form of heat.
• Transition State: Unstable state of reactants that allows reaction to occur.

EXAMPLES OF EXERGONIC REACTIONS

• Breakdown of gasoline requires a spark to exceed activation energy, leading to exergonic reactions.

LAWS OF THERMODYNAMICS

• First Law: Energy cannot be created or destroyed.
• Second Law: Energy transfer is inefficient; some energy is lost as heat, increasing entropy.

ATP: ADENOSINE TRIPHOSPHATE

• ATP provides energy for endergonic reactions through hydrolysis.

ATP STRUCTURE

• Composed of adenosine and three phosphate groups:
  • Bonds between phosphates are high-energy; breaking them releases energy.

ATP HYDROLYSIS

• ext{ATP} + ext{H}_2 ext{O}
  ightarrow ext{ADP} + ext{Pi} + ext{free energy}
• $ext{ΔG} = -7.3 ext{ kcal/mol}$

SODIUM-POTASSIUM PUMP

• Uses energy from ATP hydrolysis to pump Na⁺ out and K⁺ into cells.

ENZYMES

• Proteins that act as catalysts, speeding up reactions by lowering activation energy.
• Highly specific, catalyzing single reactions.

ENZYME-SUBSTRATE SPECIFICITY

• Determined by the 3D shape of enzyme and substrates at the active site.

INDUCED FIT

• Enzyme shape changes slightly to optimize reaction conditions at the active site.

HOW ENZYMES LOWER ACTIVATION ENERGY

• Methods include aligning substrates, providing optimal environments, and contorting substrates to make them less stable.

ENZYME REGULATION

• Enzyme activity can be regulated by environmental factors (temperature, pH) and availability of cofactors/coenzymes.

ENZYME INHIBITION

• Competitive Inhibitors: Compete with substrates for active sites.
• Noncompetitive Inhibitors: Bind to the enzyme elsewhere, slowing reaction rates.

FEEDBACK INHIBITION IN METABOLIC PATHWAYS

• Metabolic pathways regulated by end products inhibiting upstream steps to maintain homeostasis, e.g., ATP as an inhibitor in respiration.

ENZYME COFACTORS

• Some require inorganic ions (e.g., Zn²⁺, Mg²⁺) or organic molecules (coenzymes like ATP).

DRUG DISCOVERY AND ENZYMES

• Development of pharmaceutical drugs often targets enzyme inhibitors in metabolic pathways.