Metabolic Pathway

Understanding Metabolic Pathways

Definition

Metabolic pathways are integrated and controlled sequences of enzyme-catalysed reactions that occur within a cell. These pathways are essential for energy production, the synthesis of biomolecules, and the maintenance of cellular functions.

Integrated Nature

Metabolic pathways involve a series of interconnected reactions where the product of one reaction becomes the substrate for the next, creating a chain of events.

Characteristics of Metabolic Pathways

1. Reversible Steps

• Explanation: Metabolic pathways can contain reversible steps where the direction of the reaction can change depending on cellular needs.
• Example: Glycolysis, a central metabolic pathway, contains reversible steps that can operate in both glycolytic and gluconeogenic directions.

2. Irreversible Steps

• Explanation: Some reactions within metabolic pathways are irreversible, meaning they can only proceed in one direction.
• Example: The conversion of glucose to glucose-6-phosphate by hexokinase is an irreversible step in glycolysis.

3. Alternative Routes

• Explanation: Metabolic pathways often have alternative routes or branches to allow flexibility in responding to different cellular demands.
• Example: The pentose phosphate pathway is an alternative route branching from glycolysis that generates NADPH and ribose-5-phosphate.

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Metabolic Pathways - Integrated & Controlled Reactions

Anabolic and Catabolic Reactions

Anabolic Reactions

• Definition: Anabolic reactions involve the synthesis of large molecules from smaller molecules and require energy input.
• Example: Protein synthesis and DNA replication are examples of anabolic processes in which amino acids or nucleotides are assembled into complex molecules.

Catabolic Reactions

• Definition: Catabolic reactions involve the breakdown of large molecules into smaller molecules, releasing energy in the process.
• Example: Glycolysis, which breaks down glucose into pyruvate, is a catabolic pathway that generates energy in the form of ATP.

Measurement of Metabolic Rate

1. Using Simple Respirometers

• Explanation: Simple respirometers can measure an organism's metabolic rate by monitoring changes in oxygen consumption or carbon dioxide production.
• Example: A closed system respirometer measures the rate at which an organism consumes oxygen and produces carbon dioxide, providing insights into its metabolic activity.

2. Experiments to Measure Metabolic Rate

• Explanation: Experiments involving oxygen, carbon dioxide, and temperature probes can be conducted to measure metabolic rate accurately.
• Example: Using oxygen probes, researchers can assess the rate of oxygen consumption in an organism during various activities or under different conditions, helping to understand its metabolic demands.

Significance of Metabolic Pathways

1. Energy Production

Metabolic pathways play a central role in generating energy for cellular activities through processes like glycolysis and oxidative phosphorylation.

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Metabolic Pathways—Integrated & Controlled Reactions

2. Biomolecule Synthesis

Anabolic pathways within metabolism facilitate the synthesis of essential biomolecules such as proteins, nucleic acids, and lipids.

3. Homeostasis

Metabolic pathways help maintain internal stability by regulating energy production and nutrient utilisation in response to changing conditions.

Summary