Biology Chapter 8: Metabolism and Energy

Chapter 8: An Introduction to Metabolism

• Metabolism is the sum total of an organism's chemical reactions, which transforms matter and energy, subject to the laws of thermodynamics. It's an emergent property of life.

• Metabolic pathways are a series of defined steps that alter a specific molecule to produce a specific product. Each step is catalyzed by a specific enzyme.

• Catabolic pathways break down complex molecules to simpler ones, releasing energy. Cellular respiration is a major catabolic pathway that breaks down glucose for energy (glucose + oxygen → carbon dioxide + water.)

• Anabolic pathways, also known as biosynthetic pathways, consume energy to build complicated molecules from simpler ones. Examples include the synthesis of amino acids and proteins.

• Energy released from catabolic pathways powers anabolic pathways.

Energy Transformations

• Energy is the capacity to cause change. Kinetic energy is energy associated with motion (e.g., thermal energy); potential energy is energy that matter possesses due to its location or structure (e.g., light, chemical energy). Chemical energy is potential energy available for release in chemical reactions.

• Thermodynamics studies energy transformations. An isolated system doesn't exchange energy or matter with its surroundings; an open system does. Organisms are open systems.

• The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed.

• The second law of thermodynamics states that every energy transfer or transformation increases the entropy (disorder) of the universe.

• Spontaneity is the tendency of a process to occur without external influence. Spontaneous processes increase the entropy of the universe. An exergonic reaction is a spontaneous chemical reaction that releases free energy (negative ΔG), while an endergonic reaction is a nonspontaneous reaction requiring an energy input (positive ΔG). Reactions are reversible when at equilibrium (ΔG=0).

Enzymes

• Enzymes are biological catalysts that speed up metabolic reactions by lowering the activation energy (EA) needed for a reaction, required for reactants to reach a transition state, without being consumed.

• Enzymes are substrate specific, meaning they bind to specific substrates and their reaction occurs at a specific region: the active site.

• Induced fit describes the change in shape of an enzyme as it binds to a substrate (interactions between chemical groups, resulting in a more favorable orientation for the reaction). This brings the active site's chemical groups into the optimal position to catalyze the reaction.

Enzymes and Metabolic Control

• Metabolic enzymes are controlled via allosteric regulation, where a regulatory molecule binds at a site other than the active site, thus changing enzyme shape to either inhibit or stimulate its activity.

• Feedback inhibition occurs when an end product of a metabolic pathway stops an earlier enzyme, preventing overproduction. Cells compartmentalize pathways to regulate metabolism.

• Other regulatory mechanisms include the location of enzymes within membranes or organelles.

This quiz covers the fundamentals of metabolism including metabolic pathways, catabolic and anabolic processes, and energy transformations. Understand the intricacies of how organisms transform matter and energy while adhering to the laws of thermodynamics.