Metabolism

Overview

  • Definition of Metabolism:

    • Metabolism is the sum of all chemical reactions in an organism.

    • It is organized into biochemical pathways.

  • Bioenergetics: The study of how energy flows through a system.

    • Energy (E): The ability to do work.

  • Forms of Energy:

    • Kinetic Energy: Energy of movement.

    • Thermal Energy: Heat generated by molecular and atomic movement.

    • Potential Energy: Stored energy, ready for use.

    • Chemical Energy: Energy stored in chemical bonds.

Metabolic Principles

Laws of Thermodynamics

  • First Law: Conservation of Energy

    • Energy cannot be created nor destroyed, only rearranged.

  • Second Law: Increased Entropy

    • Each transfer of energy contributes to increased entropy (disorder).

    • Living organisms tend to build order and work against entropy, though they do not disrupt the entire system.

    • The release of heat as a byproduct contributes to the entropy of surroundings.

Metabolic Pathways

Definition

  • Metabolic pathways consist of a series of chemical reactions that:

    • Start with a particular reactant.

    • End with a particular product.

    • Utilize a series of enzymes to catalyze each step in the reaction series.

Types of Pathways

  • Anabolic Pathways:

    • Function: Build or synthesize larger molecules from smaller ones.

  • Catabolic Pathways:

    • Function: Break down larger molecules into smaller ones.

Types of Chemical Reactions

Energy Reactions

  • Endergonic Reactions:

    • Absorb and utilize energy from the surroundings to build products.

  • Exergonic Reactions:

    • Release energy into the environment during the formation of products.

  • Coupling of endergonic and exergonic reactions contributes to pathways.

ATP/ADP Cycle

Function

  • Energy Coupling:

    • ATP is the intermediary molecule that captures, transfers, and releases energy.

    • ATP allows the cell to perform chemical work, transport work, and mechanical work.

Hydrolysis of ATP

  • ATP releases energy when phosphate (Pi) breaks off, resulting in ADP.

    • High Energy Phosphate Bonds:

    • Not necessarily a ‘stronger' bond.

    • High potential energy like a coiled spring or two similar magnetic poles forced to coexist side by side.

  • Phosphorylation of ADP:

    • Energy captures through adding Pi to ADP forms ATP.

Enzymes and Catalysts

Enzyme Characteristics

  • All enzymes are proteins; however, not all proteins are enzymes.

  • Most enzymes catalyze reactions by:

    • Lowering activation energy (EA).

    • Increasing the reaction rate.

    • Being left unconsumed by the reaction.

Activation Energy

  • Activation Energy (E) is the energy needed to start a chemical reaction, which includes the energy required to initially break the bonds of reactants.

    • This is typically provided by heat, but excessive heat can denature proteins.

    • Enzymes lower activation energy, enabling specific reactions without causing denaturation.

Enzyme Structure and Function

Key Components

  • Substrate: A reactant upon which an enzyme acts.

  • Enzyme-Substrate Complex: The joined enzyme and substrate.

  • Active Site: The region of the enzyme that binds the substrate.

    • The induced fit mechanism allows for a specific conformational change that enhances the binding and catalysis.

    • Weak hydrogen and ionic bonds help keep the substrate in the active site for maximum efficiency.

Disruption of Enzymes

  • Enzymes can be disrupted by factors such as temperature and pH.

    • Optimal Conditions:

    • Body temperature is optimal for enzyme action.

    • Ideal pH level for blood is between 6-8.

    • Specific enzymes evolved for various physiological conditions (e.g., specific enzymes in the stomach).

Cofactors and Coenzymes

Definitions

  • Cofactor: A nonprotein helper needed for catalytic activity, often consisting of metal ions such as zinc, iron, or copper.

  • Coenzyme: An organic molecule that acts as a cofactor, often derived from vitamins consumed or synthesized by the body.

Enzyme Inhibition

Types of Inhibition

  • Competitive Inhibition:

    • Occurs when substrate molecules mimic the true substrate and compete for the active site.

    • Example: Someone stealing your parking spot (competition for the same spot).

  • Noncompetitive Inhibition:

    • Involves binding to other parts of the enzyme, changing its shape and inhibiting its function.

    • Example: Sneaking in the backdoor to ‘lock’ the front door.

Regulation of Enzymes

Allosteric Regulation

  • Involves binding of a regulatory molecule at a location other than the active site, which can either activate or inhibit the enzyme as needed, thus resulting in functional modulation.

Feedback Inhibition

  • A metabolic pathway can be stopped by the product it creates. This mechanism prevents the overproduction of proteins, energy molecules, etc.