Energy and Metabolism

• Most energy for living organisms comes from the sun
• Energy sources include:
  • Photosynthesis
  • Evaporation and precipitation
  • Wind
  • Fossil fuels comprised of 250 million-year-old photosynthetic organisms
• Rare organisms use alternative energy such as thermal vents in the ocean
• Some very rare fungus uses energy from radiation

Harnessing the Sun's Energy

• Photosynthesis uses sunlight to convert water and carbon dioxide into complex organic molecules like sugar
• Light energy converted to potential energy stored in covalent bonds of organic molecules

Energy: The Capacity to Do Work

• Two states of energy:
  • Potential: Stored energy such as chemical or physical
  • Kinetic: Energy of motion

The Laws of Thermodynamics

• 1st law of thermodynamics: Energy cannot be created nor destroyed, only transformed
• During each conversion, some energy dissipates into the environment as heat
• Energy flows continuously through the biological world; new energy from the sun replaces energy lost as heat
• 2nd law of thermodynamics: Energy can't be transformed with 100% efficiency; unavailable energy increases randomness or disorder, called entropy
• All reactions in the universe tend toward disorder like diffusion
• Order requires more energy than disorder

Gibb's Free Energy

• In a cell, free energy is denoted as G (Gibb's free energy), which is the energy available to do work
• Reactions are either Endergonic or Exergonic
• Reactions that require G to proceed where the energy in the bonds of products is higher than those of reactants are called endergonic
  • Products have more free energy than reactants
  • Not spontaneous, requires an input of energy
• Reactions that release G, where the energy in the bonds of products is lower than reactants, are exergonic
  • Products have less free energy than reactants
  • Spontaneous but may not be instantaneous
• Exergonic reactions happen spontaneously and increase disorder
• Spontaneous reactions aren't the same as instantaneous reactions and may happen at a slow rate
• Spontaneous reactions often require activation energy, which is energy required to fuel the reaction

Oxidation-Reduction (REDOX)

• Electrons can pass from one atom/molecule to another in some chemical reactions
• Oxidation: Process where an atom/molecule loses an electron and is oxidized
• Reduction: Process where an atom/molecule gains an electron and is reduced, electrons are always gained and lost together
• Process:
  • Glucose gets oxidized by oxygen into carbon dioxide, oxygen acts as the oxidizer
  • Oxygen is reduced by accepting the electrons and hydrogen to produce water, oxidation + reduction
  • The oxidizer may be any atoms that can accept electrons

Activation Energy

• Is required to destabilize existing bonds to start a chemical reaction
• Rate of an exergonic reaction depends on the activation energy required
• Rate can be increased by:
  • Increasing energy of reacting molecules (heating)
  • Lowering activation energy with a catalyst (enzyme)
• Catalyst:
  • Substances influence chemical bonds to lower activation energy
  • Is not consumed in the reaction
  • Cannot make an endergonic reaction spontaneous

Metabolism

• Is the total of all chemical reactions carried out by an organism
  • Catabolic reactions (catabolism): Chemical reactions that harvest energy by breaking down molecules
  • Anabolic reactions (anabolism): Chemical reactions that use energy to build up molecules

Catabolism - Adenosine Triphosphate (ATP

• Catabolism creates Adenosine Triphosphate (ATP) which is the primary energy "currency" used by cells
• ATP is not suitable for long-term energy storage
  • Phosphate bonds are too unstable
  • Fats and carbohydrates store energy better
  • Cells store only a few seconds' worth of ATP

ATP is Composed Of:

• Ribose: Five-carbon sugar
• Adenine
• Chain of three phosphates:
  • Key to energy storage
  • PO4 groups are highly negatively charged and strongly repel each other
  • Bonds between PO4 are unstable and release energy when broken
  • ATP hydrolysis drives endergonic reactions
  • ATP has low activation energy

Explore enzymes, thermodynamics, and ATP's role in metabolism. Learn about reaction types and energy transfer in ecosystems. Understand Gibbs free energy, photosynthesis, and redox reactions.