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.