chp 8 cell Metabolism

Chapter 8: An Introduction to Metabolism

Overview of Metabolism

  • Metabolism is the sum of an organism’s chemical reactions organized into pathways.

  • Metabolic pathways start with a specific molecule and end with a product.

  • Steps are catalyzed by specific enzymes:

    • Enzyme 1 -> Reaction 1 -> Starting molecule -> Enzyme 2 -> Reaction 2 -> Enzyme 3 -> Reaction 3 -> Product.

Types of Metabolic Pathways

Catabolic Pathways

  • Function: Break down complex molecules into simpler compounds, releasing energy.

  • Example: Cellular respiration

    • Inputs: Oxygen + Sugar.

    • Outputs: Carbon Dioxide + Water + ATP.

Anabolic Pathways

  • Function: Build complex molecules from simpler ones, requiring energy.

  • Example: Protein synthesis from amino acids.

Forms of Energy

  • Energy is the capacity to cause change.

  • Kinetic Energy: Energy of motion.

  • Potential Energy: Energy due to an object's location or structure.

  • Chemical energy available for reactions (e.g., glucose).

The Laws of Thermodynamics

First Law of Thermodynamics

  • Energy of the universe is constant.

  • Energy can be transferred and transformed but cannot be created or destroyed.

  • Some energy is lost as heat during transfers.

Second Law of Thermodynamics

  • Energy transformations increase the entropy (disorder) of the universe.

  • Entropy increases in spontaneous processes, whereas nonspontaneous processes decrease entropy and require energy.

Free Energy Change (ΔG)

  • Determines spontaneity of reactions:

    • Reactions with negative ΔG are spontaneous (exergonic).

    • Reactions with positive ΔG require energy (endergonic).

ATP and Cellular Work

  • ATP couples exergonic and endergonic reactions, managing energy resources via energy coupling.

  • ATP Structure:

    • Adenosine Triphosphate (ATP) has three phosphate groups.

    • Hydrolysis of ATP releases energy.

  • Energy from ATP hydrolysis drives endergonic reactions by phosphorylation of reactants.

Enzymes and Metabolism

Role of Enzymes

  • Enzymes are proteins that speed up reactions without being consumed.

  • They lower the activation energy (EA) needed for reactions to occur.

Enzyme Activity

  • Enzymes bind to substrates forming an enzyme-substrate complex.

  • The active site lowers the EA barrier via:

    • Orienting substrates correctly.

    • Straining substrate bonds.

    • Providing a favorable microenvironment.

Factors Affecting Enzyme Activity

  • Temperature and pH: Each enzyme has optimal conditions for activity.

  • Cofactors: Non-protein helpers assisting enzymes (e.g., inorganic metals, organic coenzymes like vitamins).

Regulation of Enzyme Activity

  • Metabolic pathways must be tightly regulated to avoid chaos.

  • Mechanisms include:

    • Switching genes on or off.

    • Regulating enzyme activity through allosteric regulation.

  • Inhibition:

    • Competitive inhibitors bind to the active site.

    • Non-competitive inhibitors bind elsewhere affecting enzyme shape.

    • Examples: toxins, poisons, pesticides, antibiotics.

Feedback Inhibition

  • The end product of a metabolic pathway shuts down the pathway, preventing waste of resources.