New chapter focusing on enzymes and their roles in metabolism.
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Use of slides to enhance learning experience.
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).
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.
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.
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: 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.
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.
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.
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.
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).
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.