intro to met pt 1

Learning Objectives

• Understand how chemical transformations within metabolic pathways generate and store energy.

• Identify key steps in the following metabolic pathways:

  • Glycolysis and gluconeogenesis

  • Tricarboxylic acid (TCA) cycle (also known as the citric acid cycle or Krebs cycle)

  • Electron transport system

  • Glycogen synthesis and breakdown

  • Fatty acid synthesis and breakdown

Introduction to Metabolism

Metabolism: The interconversion of chemicals within the cell through various steps. Each step is typically catalyzed by an enzyme (a protein catalyst), which facilitates the reaction by lowering the activation energy required. Metabolic pathways can be interconnected, allowing metabolites to move between them and contributing to a complex regulatory network.Each pathway has a characteristic number of steps; for example, glycolysis consists of 10 distinct reactions that convert glucose into pyruvate, yielding ATP and NADH as energy currency.

Types of Metabolism

Catabolic Reactions

• Definition: Degradative reactions that are typically oxidative, breaking down complex molecules.

• Functions:

  • Produce chemical energy, mainly in the form of ATP, that powers cellular processes.

  • Generate mechanical energy essential for muscle contraction and movement.

  • Create reducing equivalents such as NADH and NADPH, providing necessary electrons for various biosynthetic reactions.

  • Break down complex substrates into simpler biosynthetic precursors which can be reused in anabolic pathways.

Anabolic Reactions

• Definition: Biosynthetic reactions that focus on the assembly of smaller units into larger biomolecules.

• Functions:

  • Store energy by synthesizing glucose and converting it to glycogen in liver and muscle cells for future use.

  • Produce macromolecules like proteins, nucleic acids, and lipids, essential for cell structure and function.

  • Contribute to the formation of cellular structures, thus maintaining tissue integrity and nutrient storage.

Thermodynamics in Metabolism

• Importance of Gibbs free energy (ΔG) in metabolic reactions, guiding spontaneity and directionality of reactions.

• Equation: ΔG = ΔG° + RT ln ([products]/[reactants])

  • ΔG°: standard Gibbs free energy change, representing energy under standard conditions.

  • R: gas constant (8.314 J/K/mol), linking energy changes to temperature.

  • T ≈ 310.15 K (approx. 37°C) in higher organisms, indicating normal physiological temperatures.

• Biological systems are not in equilibrium but exist in a dynamic flux, where metabolites traverse pathways at varying speeds and concentrations, ensuring constant energy production and consumption.

Nature of Reactions

Many biological reactions are endothermic, meaning they require an input of energy to proceed. In these cases, the coupling of exergonic reactions (reactions that release energy) can provide the necessary energy for endergonic processes, facilitating efficient metabolic functioning within cells. This interplay emphasizes the importance of metabolic regulation and the role of enzymes in maintaining cellular homeostasis.