BSC1010 Lecture 8a

Chapter 6: An Introduction to Metabolism

1. Overview of Metabolism

  • The chemistry of life is organized into metabolic pathways.

  • Organisms transform energy through various biochemical processes.

  • Energy transformations are governed by the two laws of thermodynamics.

  • Organisms utilize free energy for survival and function.

  • ATP is the primary energy currency of the cell, linking exergonic (energy-releasing) reactions to endergonic (energy-consuming) reactions.

2. Metabolic Pathways

A. Types of Metabolic Pathways

  • Catabolic Pathways:

    • Release energy by breaking down complex molecules into simpler compounds.

    • Example: Cellular respiration where energy-rich substrates are converted into energy-poor products.

  • Anabolic Pathways:

    • Consume energy to construct complex molecules from simpler ones.

    • Example: Photosynthesis where energy is used to synthesize glucose from carbon dioxide and water.

B. Energy Flow in Metabolism

  • Energy from catabolic pathways provides the necessary energy for anabolic pathways.

  • The flow of energy is fundamental to life's processes, with a dynamic interplay between breaking down substances and building new molecules.

3. Forms of Energy

A. Potential Energy

  • Defined as the energy possessed by an object due to its position or structure.

  • Example: Gravitational potential energy, given by the formula PE = mgh, where:

    • PE = potential energy in Joules or Calories,

    • m = mass in kilograms,

    • g = gravitational acceleration (9.8 m/sec²),

    • h = height in meters.

B. Kinetic Energy

  • Refers to the energy of motion.

  • Examples include the motion of objects, photons, and heat.

  • Kinetic energy is calculated using KE = (1/2)mv², where:

    • KE = kinetic energy in Joules or Calories,

    • m = mass in kilograms,

    • v = velocity in meters/second.

4. Thermodynamics

  • First Law of Thermodynamics: Energy can be transformed or transferred, but it cannot be created or destroyed.

  • Second Law of Thermodynamics: Every energy transformation increases the disorder (entropy) of the universe.

    • Entropy is a measure of disorder, with an increase in heat representing a random molecular motion.

A. Energy Transformations and Heat

  • Energy transformations often convert ordered forms of energy to heat, which is generally unutilizable for work.

  • Example: Automobiles convert only 25% of gasoline energy into motion; the remainder is lost as heat.

5. Open and Closed Systems

  • System: The matter under study; Surroundings: Everything outside the system.

  • Closed systems (like liquid in a thermos) are isolated from their surroundings, while open systems (like living organisms) exchange energy and matter.

    • Organisms are open systems, absorbing energy and releasing metabolic waste.

6. Spontaneous and Nonspontaneous Processes

A. Spontaneous Processes

  • Occur without energy input and lead to increased stability in a system.

  • Example: Processes that result in chemical reactions favoring lower energy configurations.

B. Nonspontaneous Processes

  • Require energy input to proceed and decrease system stability.

  • Example: Anabolic reactions, such as synthesizing carbohydrates.

7. Free Energy (G)

A. Concept of Free Energy

  • Free energy is the portion of a system's energy available to perform work.

  • Defined mathematically as ΔG = G final state - G initial state.

B. Stability and Free Energy

  • Systems high in free energy are unstable and tend to evolve toward lower energy states, releasing energy in the process.

  • Spontaneous processes have negative ΔG, while nonspontaneous processes exhibit positive ΔG.

8. Chemical Reactions and Energy

A. Exergonic Reactions

  • Release free energy, categorized as spontaneous processes with negative ΔG.

  • Example: Cellular respiration, where glucose is converted to carbon dioxide and water, releasing 686 kcal/mol.

B. Endergonic Reactions

  • Absorb free energy, classified as nonspontaneous with positive ΔG.

  • Photosynthesis serves as an example, requiring energy input for glucose synthesis.

9. Equilibrium and Metabolic Processes

A. Equilibrium in Systems

  • A system at equilibrium (ΔG = 0) is at maximum stability and can do no work.

  • Chemical reactions in equilibrium have equal rates for the forward and backward reactions.

B. Metabolic Disequilibrium

  • Living cells maintain a state of disequilibrium to sustain life processes, continually exchanging materials to prevent reaching equilibrium.

10. Cellular Energy Work

  • Cells perform three primary types of work:

    • Mechanical Work: Movements such as cilia beating and muscle contractions.

    • Transport Work: Movement of substances across membranes against concentration gradients.

    • Chemical Work: Drive endergonic reactions like synthesizing polymers from monomers.

11. ATP: The Energy Currency

A. Structure of ATP

  • ATP (adenosine triphosphate) consists of adenine, ribose, and three phosphate groups.

B. Energy Release and Regeneration

  • Energy is released during the hydrolysis of ATP, converting it to ADP and inorganic phosphate, with a ΔG of about -13 kcal/mol.

  • ATP is continually regenerated from ADP, requiring an energy investment of 7.3 kcal/mol through phosphorylation.