Module 4: Bioenergetics Reactions

Module 4: Bioenergetics Reactions

• Bioenergetics is the study of energy in living systems and the organisms that utilize them (plants and animals).

What is Energy?

• Energy is required by all organisms.
• Energy can be kinetic or potential.

Kinetic Energy

• Is the energy of motion.
• Examples include heat and light energy.

Potential Energy

• Is the energy of position.
• Includes energy stored in chemical bonds.

Two Types of Energy Reactions

• Endergonic Reactions (Chloroplast):

  • These chemical reactions require a net input of energy.
  • Photosynthesis is an example of an endergonic reaction.
  • Photosynthesis uses light energy from the sun to convert carbon dioxide and water into glucose and oxygen.

• Exergonic Reactions (Mitochondria):

  • These chemical reactions release energy.
  • Cellular respiration is an example of an exergonic reaction.
  • Cellular respiration breaks down glucose and oxygen to produce carbon dioxide, water, and ATP (energy).

Mitochondria and Chloroplasts

• Mitochondria:

  • Found in nearly all eukaryotic cells (plants, animals, fungi, and most protists).
  • Sites of cellular respiration, generating ATP by extracting energy from sugars, fats, and other fuels using oxygen.
  • Often hundred or thousands per cell.
  • Enclosed by two membranes (phospholipid bilayers) with embedded proteins.
  • Inner membrane has two compartments:
    • Intermembrane space: The area between the inner and outer membranes.
    • Mitochondrial matrix: The area enclosed by the inner membrane.

• Chloroplasts:

  • Found in plants and algae.
  • Sites of photosynthesis.
  • Convert light energy to chemical energy.
  • Have three compartments:
    • Intermembrane space
    • Stroma
    • Thylakoid space
  • Chloroplasts contain thylakoids (membranous systems).
  • Stacked thylakoids form a granum.
  • The fluid outside the thylakoids is the stroma (contains DNA and ribosomes).
  • Contain amyloplasts (colorless plastids that store starch).

Peroxisomes: Oxidation

• Peroxisomes: Specialized organelles bounded by a single membrane containing enzymes that transfer hydrogen from substances to oxygen, producing hydrogen peroxide (H₂O₂).
• In the liver, peroxisomes detoxify alcohol and other harmful compounds.
• Glyoxysomes: Specialized peroxisomes in plant fat-storing tissues that convert fatty acids to sugar.

Metabolism

• The sum of all chemical activities in a cell.
• Two types:
  • Anabolic pathways: Consume energy to build complex molecules from simpler ones. Example: Photosynthesis (building glucose).
  • Catabolic pathways: Release energy by breaking down complex molecules to simpler ones. Example: Cellular respiration (breaking down glucose)

Adenosine Triphosphate (ATP)

• Primary energy currency of cells.
• Components:
  • Adenine: Nitrogenous base
  • Ribose: Five-carbon sugar
  • Three phosphate groups which have high energy bonds.
• The last phosphate group (PO₄) contains the most energy.

Breaking the Bonds of ATP

• The process is called phosphorylation.
• Occurs continually in cells.
• ATP-ase weakens the last phosphate bond.
• Free PO₄ (phosphate) and energy are released.

How Does ATP Work?

• Organisms use enzymes to break down glucose to release potential energy.
• This released energy is stored in ATP.

How Much ATP Do Cells Use?

• Approximately 10 million ATP molecules are generated and consumed per cell per second.

Coupled Reaction - ATP

• Exergonic hydrolysis of ATP is coupled with endergonic dehydration processes by transferring a phosphate group to another molecule.

Hydrolysis of ATP

• ATP + water (H₂O) → ADP + phosphate (P) (exergonic)

Hydrolysis is Exergonic

• The process of releasing energy from ATP through hydrolysis is an exergonic reaction.

Dehydration of ATP

• ADP + phosphate (P) → ATP + water(H₂O) (endergonic)

Dehydration is Endergonic

• The process of converting ADP to ATP is an endergonic process that stores energy in chemical bonds.