BIOS3010-week 31 introduction to metabolism

Introduction to Enzymes in Metabolism

  • New chapter focusing on enzymes and their roles in metabolism.

  • Course attendance registration encouraged.

  • Use of slides to enhance learning experience.

Definition of Metabolism

  • Metabolism: The sum of all biochemical reactions in a cell; can be divided into two categories:

    • Catabolism: Breakdown of larger molecules into smaller ones, usually releasing energy (e.g., breakdown of glucose into pyruvate).

    • Anabolism: Building up larger molecules from smaller ones, usually requiring energy (e.g., protein synthesis from amino acids).

Overview of Metabolic Processes

  • Enzymes act as catalysts for metabolic reactions, allowing multiple reactions to happen simultaneously in a coordinated manner.

  • Metabolic pathways consist of sequential reactions, akin to train routes or the London Underground, where substrates travel through stations (reactions) catalyzed by enzymes.

Metabolic Pathways

  • Sequential Reactions: Enzymatic reactions can be represented as pathways where each enzyme catalyzes a specific step.

    • Example: Transitioning from substrate A to B catalyzed by enzyme E1, and from B to C by E2.

    • Research can determine the sequence of reactions based on the time taken for substrate conversion.

  • Branching: Metabolic pathways can diverge, allowing substrates to follow different reactions based on cellular needs.

Concepts of Flux in Metabolic Pathways

  • Flux: The measure of how much substrate flows through a metabolic pathway, similar to the flow of water in a river.

  • Flux Control Coefficient: Indicates how changes in enzyme parameters can affect the overall flux of the pathway (e.g., altering enzyme efficiency).

Steady State in Metabolism

  • Steady State: Condition where the influx of substances into a pathway equals the outflux, maintaining stable concentrations of intermediates within the pathway.

  • Example: In a bathtub, the water level remains constant when inflow equals outflow.

Driving Forces in Metabolic Pathways

  • The direction of metabolic pathways is influenced by free energy change (ΔG).

    • If ΔG is negative, the reaction is favorable (spontaneous).

    • The equation ΔG = ΔG°' + RT ln Q describes the relationship between concentration and the reaction's favorability.

    • ATP is a common energy currency generated during favorable reactions.

Regulation of Metabolic Pathways

  • Positive Feedforward Loop: An upstream substrate activates an enzyme, promoting the production of a downstream product.

  • Negative Feedback Loop: Accumulation of product inhibits its own further production, maintaining stability in the pathway (homeostasis).

  • Positive Feedback Loop: Product stimulates its own production, potentially leading to rapid increases in concentration.

Oscillations in Regulation

  • Complex Feedback Mechanisms: When multiple compounds inhibit each other, they can lead to unstable oscillations rather than steady states.

  • The dynamics of oscillations can be demonstrated in biological processes like the cell cycle or hormonal cycles.

Importance of Protein Phosphorylation

  • Kinases and Phosphatases: Enzymes that respectively add and remove phosphate groups from proteins, thereby regulating their activity.

    • A balance between kinase and phosphatase activities determines the phosphorylated state of the proteins, acting like a switch.

  • Zero-Order Ultrasensitivity: A phenomenon where small changes in the concentrations of kinases or phosphatases can lead to significant changes in the overall state of the pathway (active vs. inactive).

Conclusion

  • Metabolic pathways involve complex interactions and regulations that can be simplified into feedback loops and flux measurements.

  • Understanding these principles helps in grasping how cells maintain homeostasis and react to changes in their environment.

robot