Chap 8 slides info

Introduction to Metabolism

Course: BSC1010C - General Biology I at Valencia College

Chapter: 8 - An Introduction to Metabolism

Instructor: Dr. Daniel Sanches

The Energy of Life

Living cells operate as intricate chemical factories, engaged in thousands of biochemical reactions essential for life. Cellular respiration is a crucial process through which cells extract energy from sugars, fatty acids, and other organic fuels to perform vital cellular work, enabling organisms to grow, reproduce, and maintain homeostasis. Interestingly, some organisms possess the capability to convert energy into light, which is a phenomenon known as bioluminescence, commonly observed in certain species of jellyfish and fireflies.

Overview of Metabolism

Metabolism encompasses all chemical reactions that occur within an organism, embodying the emergent property of life that results from complex interactions between various molecules. Metabolic pathways consist of a series of sequential biochemical reactions, starting from specific reactants and leading to particular products; each step in these pathways is catalyzed by specific enzymes that enhance the reaction rate without being consumed.

Catabolic and Anabolic Pathways

• Catabolic Pathways: These pathways release energy by breaking down complex molecules, such as carbohydrates, lipids, and proteins, into simpler compounds. A notable example is cellular respiration, where glucose is oxidized in the presence of oxygen to release energy, carbon dioxide, and water.

• Anabolic Pathways: In contrast, anabolic pathways consume energy to synthesize complex molecules from simpler ones. For instance, the synthesis of proteins involves linking amino acids together through peptide bonds, a process that requires input energy.

Bioenergetics

Bioenergetics is the field of study concerning the flow of energy in living organisms, focusing on how energy is transformed and utilized during biological processes. Understanding bioenergetics is essential for exploring cellular respiration, photosynthesis, and energy metabolism in living systems.

Forms of Energy

Energy is defined as the capacity to cause change and exists in various forms:

• Kinetic Energy: The energy associated with the motion of objects, including molecular movement.

• Thermal Energy: This is kinetic energy linked to the random movement of molecules, significantly affecting temperature.

• Potential Energy: The stored energy based on an object’s position or structure; for instance, chemical bonds store potential energy in molecules.

• Chemical Energy: A form of potential energy available in chemical reactions that can be released during transformations.

Energy transformations can occur among these different forms, demonstrating the interconnectedness of physical processes.

Laws of Energy Transformation

• Thermodynamics: The branch of physics that deals with energy transformations.

• Isolated System: An isolated system cannot exchange energy or matter with its surroundings, such as a closed liquid in a thermos.

• Open System: Open systems, such as organisms, exchange energy and matter with their environment.

• First Law of Thermodynamics: States that energy cannot be created or destroyed, only transformed from one form to another.

• Second Law of Thermodynamics: Expresses that energy transformations inevitably lead to an increase in the universe's entropy (disorder) over time.

Free-Energy Change in Reactions

The free-energy change (ΔG) of a reaction provides information on its spontaneity:

• A negative ΔG indicates spontaneous processes that can occur without external energy input.

• Free energy changes are related to changes in enthalpy (ΔH), entropy (ΔS), and temperature (T), represented by the equation: ΔG = ΔH - TΔS.

Free Energy, Stability, and Equilibrium

Free energy is a measure of a system's instability and its inclination towards a more stable, lower energy state. Spontaneous changes tend to decrease free energy, driving systems toward equilibrium. At equilibrium, a system reaches a state of maximum stability, where the forward and reverse reactions occur at equal rates, influencing the biological processes that strive for metabolic efficiency.

Exergonic and Endergonic Reactions

• Exergonic Reactions: These reactions release free energy, resulting in a net decrease in free energy (ΔG < 0); they are spontaneous reactions that can proceed without requiring energy from external sources.

• Endergonic Reactions: These reactions require an input of free energy, resulting in a net increase in free energy (ΔG > 0); they are non-spontaneous and need energy to occur.

ATP and Cellular Work

ATP (Adenosine Triphosphate) functions as the primary energy currency in cells, coupling exergonic and endergonic reactions to fuel cellular activities. The main types of cellular work include:

• Chemical Work: Involving driving biochemical reactions necessary for cellular functions.

• Transport Work: Enabling the movement of substances across cellular membranes against concentration gradients.

• Mechanical Work: Facilitating muscle contraction and other movements in cells.

ATP hydrolysis releases energy through the breaking of phosphate bonds, allowing energy coupling to drive various cellular reactions efficiently.

Enzymes: Catalysts in Metabolism

Enzymes are biological catalysts, primarily proteins, that accelerate chemical reactions by lowering the activation energy (EA) required. While enzymes do not alter the reaction's ΔG, they significantly increase the reaction rates of processes that naturally occur. Each enzyme exhibits substrate specificity, meaning that it binds to specific substrates to form an enzyme-substrate complex, catalyzing relevant biochemical reactions with precision and efficiency.

Factors Affecting Enzyme Activity

Numerous environmental factors impact enzyme activity, including:

• Temperature: Each enzyme has an optimal temperature range for activity; extreme temperatures can denature the enzyme.

• pH: Like temperature, pH levels affect enzyme structure and function, with each enzyme having an optimal pH for activity.

• Cofactors and Coenzymes: Non-protein helpers are crucial for enzymatic functions; coenzymes, often derived from vitamins, act as transient carriers of specific atoms or functional groups.

Allosteric Regulation and Enzyme Activity

Allosteric regulation involves regulatory molecules that bind to enzymes at sites other than the active site, influencing their activity. This can lead to either activation or inhibition of the enzyme's function. Additionally, cooperativity enhances enzyme activity, where the binding of a substrate to one active site increases the likelihood of substrate binding to other active sites. Feedback inhibition is a vital regulatory mechanism that prevents excessive product formation by inhibiting pathways upstream based on the levels of certain products.

Conclusion: Metabolic Pathway Control

The regulation of enzyme activity is essential for maintaining metabolic efficiency within cells. Each metabolic pathway is localized within cellular structures, which enhances the organization and efficiency of biochemical processes, ensuring a balance between energy production and consumption in living organisms.