Lecture Notes on Energy, Thermodynamics, and Cell Processes

Types of Energy

Potential Energy

• Stored energy found in chemical bonds, e.g., gasoline, biological molecules.
• Atoms sharing electrons represent potential energy.

Kinetic Energy

• Energy in use; manifested as movement.
• Includes movement of atoms or larger entities like humans.
• Different manifestations include heat, light, electricity.
  • Light: Photons emitted by the sun.
  • Heat: Radiant energy from molecular dissipation.

Conversion Between Potential and Kinetic Energy

• Example: A bicyclist converting potential energy from food into kinetic energy while cycling.
• Energy can convert back and forth between potential and kinetic forms.

Sources of Energy

• Batteries, gasoline, biological molecules (glucose, lipids, proteins).
• Energy conversion in cells: Mitochondria convert these into ATP (potential energy).

Thermodynamics

First Law of Thermodynamics (Conservation of Energy)

• Energy cannot be created or destroyed; it only changes forms.
• Example: Burning wood converts energy into heat and light.

Second Law of Thermodynamics (Entropy)

• Energy transfer is always inefficient; some energy is lost to the environment.
• Entropy: Tendency towards disorder and randomness.
  • Example: Perfume evaporating, carbon dioxide spreading from high to low concentration.
• In biology, systems aim to maintain homeostasis despite entropy.
• Cellular reactions aim to balance concentration gradients.

Biological Reactions and Energy

Types of Reactions

• Endergonic Reaction: Absorbs energy, e.g., photosynthesis (kinetic to potential).
• Exergonic Reaction: Releases energy, e.g., breaking down glucose (potential to kinetic).
• Coupled Reaction: Combination where one reaction’s energy release fuels another’s absorption.

Role of ATP

• Acts as an energy intermediary in the cell.
• Easy to break covalent bonds in ATP due to phosphate repulsion.
• Mitochondria convert glucose to ATP, storing energy as potential.

Enzymes and Catalysis

• Enzymes lower activation energy needed for reactions.
• Facilitate dehydration synthesis (endergonic) and hydrolysis (exergonic).
• Specific to substrates and reactions they catalyze.
• Certain poisons or drugs can inhibit enzyme functions.

Cellular Transport

Passive Transport

• Simple Diffusion: Movement of molecules from high to low concentration naturally.
• Facilitated Diffusion: Requires channel proteins for charged or large molecules.
• Osmosis: Diffusion of water across a membrane.
  • Tonicity: Isotonic (equal), hypertonic (cell shrinks), hypotonic (cell swells).

Active Transport

• Moves molecules against concentration gradient (requires energy).
• Example: Neurons maintaining voltage potential through sodium-potassium pump.
• Muscles using calcium for contraction and relaxation.

Bulk Transport

• Exocytosis: Release of substances from the cell.
  • Example: Neurotransmitter release in neurons.
• Endocytosis: Taking in substances into the cell.
  • Example: White blood cells engulfing bacteria.

Final Notes

• Enzymes critical for efficient energy use and cellular reactions.
• Active transport essential for maintaining cellular homeostasis.
• Energy conservation principles guide biological and chemical processes.