Introduction Lecture on Metabolism

Prof. Kastanos, Rockville Campus, BIOL 150Presenters: Antonio del Castillo-Olivares, Evdokia Kastanos, Victoria Virador.OER project, Montgomery College, licensed under CC BY 4.0.

Metabolism Learning Objectives

By the end of this chapter, you should be able to:

• Explain Energy and Metabolism.

• Understand Potential, Kinetic, Free, and Activation Energy in detail.

• Discuss the Laws of Thermodynamics and their implications for biological processes.

• Describe ATP: Adenosine Triphosphate and its role in energy transfer.

• Explain the role of Enzymes in metabolic reactions and their regulation.

Overview of Metabolism

Metabolism encompasses all chemical reactions occurring within a cell, divided into two major categories:

• Catabolic pathways: i.e., glycolysis and Krebs cycle, break down larger molecules into smaller units, releasing the energy stored in chemical bonds.

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  Anabolic pathways: such as the synthesis of proteins and nucleic acids, build complex molecules from simpler ones and generally require energy input.Chemical reactions in metabolism are essential for energy transfer and cellular function.

Definition of Metabolism

Metabolism includes all biochemical reactions that provide energy and metabolic intermediates necessary for cellular processes such as growth, reproduction, and maintenance of cellular structures.

Catabolic and Anabolic Pathways

• Anabolism: Involves biochemical pathways that synthesize larger molecules. Requires energy, which is often sourced from ATP.

• Catabolism: Involves pathways that break down molecules into their smaller components, releasing energy that can be used for ATP production or other energy-requiring processes.

Role of Producers, Consumers, and Decomposers

• Producers: Such as plants, convert sunlight into carbohydrates through photosynthesis.

• Consumers: Heterotrophs that consume producers to obtain energy. These organisms convert carbohydrates into usable cellular energy via cellular respiration.

• Decomposers: Organisms like fungi and bacteria break down organic matter, cycling nutrients back into the ecosystem and making them available to producers once more.

Energy Transformations

Energy transformation starts with sunlight, converted into chemical energy by producers (photosynthesis), and then transferred to consumers through consumption and finally converted into work and heat during cellular respiration.

Potential and Kinetic Energy

Energy is the capacity to perform work; it exists in various forms:

• Potential Energy: Energy stored in an object due to its position or configuration (e.g., water behind a dam).

• Kinetic Energy: Energy of motion, exemplified by water flowing down from a dam, converting stored potential energy to kinetic energy.

Chemical Energy

Chemical energy, a form of potential energy, is stored in the bonds of molecules. For example, the energy released from carbon compounds like octane (in fuel) during combustion is converted into kinetic energy to power engines and other machinery.

Free Energy Change

Free energy change (ΔG) is a critical concept referring to the energy available to do work during a reaction:

• Exergonic Reactions: Reactants have more free energy than products (ΔG < 0), energy is released to the surroundings.

• Endergonic Reactions: Products have more free energy than reactants (ΔG > 0), energy is absorbed from the surroundings.

Activation Energy

Activation energy is the minimal energy required to initiate a chemical reaction. Enzymes function to lower this activation energy, enhancing the likelihood of reactants colliding and reacting without altering the overall ΔG of the reaction.

Laws of Thermodynamics

• First Law of Thermodynamics: Energy cannot be created or destroyed, only converted from one form to another (e.g., chemical energy to kinetic).

• Second Law of Thermodynamics: Entropy, or disorder, of an isolated system always increases over time. For example, the melting of ice into water represents an increase in entropy.

ATP: Cellular Energy Currency

ATP is the primary energy currency in cells, facilitating energy transfer by undergoing hydrolysis:

• Importance of ATP: Essential for various cellular processes including synthesis of macromolecules, active transport across membranes, and muscle contractions.

• Energy Released by ATP Hydrolysis: ATP hydrolysis releases substantial energy, driving many cellular processes.

• Recycling of ATP: ATP is continuously recycled through cellular respiration and other metabolic processes, maintaining a constant supply for cellular activities.

Enzymes in Metabolism

Enzymes are biological catalysts that accelerate metabolic reactions:

• Enzymatic Function: They lower the activation energy required for reactions, enabling the conversion of substrates into products without changing the overall energy dynamics of the reaction (ΔG).

• Induced Fit Model: Enzymes undergo conformational changes upon substrate binding, allowing for more precise interactions.

• Mechanisms of Enzyme Action: Enzymes can facilitate reactions by correctly orienting substrates, applying strain on substrate bonds, and creating an optimal environment for the reaction.

• Temperature and pH Influence: Enzyme activity is sensitive to temperature and pH. Extreme temperatures or pH levels can denature enzymes, disrupting their active sites.

• Role of Cofactors and Inhibitors: Many enzymes require cofactors, such as metal ions, to function. Competitive inhibitors hinder substrate binding, while noncompetitive inhibitors alter enzyme shape.

• Allosteric Regulation and Feedback Inhibition: Allosteric enzymes can exist in active and inactive forms, regulated by specific molecules that stabilize one form or another. Feedback inhibition controls metabolic pathways, averting overproduction of metabolites.