Metabolism

Definition and Overview

Metabolism refers to the totality of an organism's chemical reactions, which are essential for maintaining life. These reactions are organized into metabolic pathways, where each step is catalyzed by a specific enzyme.

• Metabolism: The sum of all chemical reactions occurring in a living organism.

• Metabolic pathway: A series of chemical reactions beginning with a specific molecule and ending with a product, each step facilitated by an enzyme.

• Example: The breakdown of glucose in cellular respiration involves multiple enzymes and steps.

Metabolic Pathways

Metabolic pathways can be classified based on their energy requirements and the direction of molecular transformation.

• Catabolic pathways: Pathways that release energy by breaking down complex molecules into simpler compounds.

  • Example: Cellular respiration, where glucose is broken down to produce ATP.

• Anabolic pathways: Pathways that consume energy to build complex molecules from simpler ones.

  • Example: Protein synthesis, where amino acids are assembled into proteins.

Metabolism and Energy

Forms of Energy

Energy is the capacity to cause change or do work. In biological systems, energy exists in various forms:

• Kinetic energy: Energy associated with motion.

• Heat (thermal energy): Kinetic energy due to the random movement of atoms or molecules.

• Potential energy: Energy that matter possesses due to its location or structure.

• Chemical energy: Potential energy available for release in a chemical reaction.

• Example: The energy stored in ATP molecules is chemical energy that can be used to power cellular processes.

Thermodynamics in Biology

Basic Principles

Thermodynamics is the study of energy transformations. Biological systems are governed by the laws of thermodynamics.

• System: The matter under study.

• Isolated system: No energy transfer with surroundings.

• Open system: Energy can be transferred between the system and its surroundings.

  • Note: Living organisms are open systems, constantly exchanging energy and matter with their environment.

The First Law of Thermodynamics

The first law, also known as the law of conservation of energy, states:

• "Energy can be transferred and transformed, but it cannot be created or destroyed."

• Equation:

• Example: The chemical energy in food is converted to kinetic energy and heat in animals.

The Second Law of Thermodynamics

The second law states:

• "Every energy transfer or transformation increases the entropy (disorder) of the universe."

• Entropy: A measure of disorder or randomness.

• Example: As animals metabolize food, some energy is lost as heat, increasing the entropy of the surroundings.

Metabolism and Free Energy

Free Energy (G)

Free energy is the portion of a system's energy that can perform work when temperature and pressure are uniform.

• Free energy (G): Energy available to do work in a system.

• Change in free energy (): Determines whether a reaction is spontaneous.

  • Exergonic reaction: Proceeds with a net release of free energy (); spontaneous.

  • Endergonic reaction: Absorbs free energy from surroundings (); non-spontaneous.

• Equation: Where is change in enthalpy, is temperature in Kelvin, and is change in entropy.

Energy Coupling and ATP

Cells perform work by energy coupling, using exergonic reactions to drive endergonic ones. ATP (adenosine triphosphate) is the primary energy carrier in cells.

• ATP hydrolysis: Releases energy that can be used to power cellular processes.

  • Equation:

• ATP regeneration: ATP is constantly regenerated from ADP and inorganic phosphate.

Metabolism and Enzymes

Role of Enzymes

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required.

• Activation energy (): The initial energy needed to start a chemical reaction.

• Catalyst: A chemical agent that speeds up a reaction without being consumed.

• Enzyme: A protein that acts as a biological catalyst.

• Example: Sucrase catalyzes the hydrolysis of sucrose into glucose and fructose.

Enzyme Mechanism

Enzymes function by binding substrates at their active site, forming an enzyme-substrate complex, and facilitating the reaction.

• Substrate: The reactant an enzyme acts on.

• Active site: The region on the enzyme where the substrate binds.

• Induced fit: The enzyme changes shape slightly to fit the substrate, catalyzing the reaction.

• Product: The result of the enzymatic reaction.

Regulation of Enzyme Activity

Enzyme activity can be regulated by various mechanisms to ensure proper metabolic control.

• Allosteric regulation: Inhibits or stimulates an enzyme's activity by binding to a site other than the active site.

• Competitive inhibitors: Bind to the active site, competing with the substrate.

• Noncompetitive inhibitors: Bind to another part of the enzyme, altering its function.

Environmental Effects on Enzymes

Enzyme activity is affected by temperature and pH, with each enzyme having optimal conditions.

• Optimal temperature: The temperature at which an enzyme's activity is highest.

• Optimal pH: The pH at which an enzyme functions best.

• Example: Pepsin (stomach enzyme) has optimal activity at low pH, while trypsin (intestinal enzyme) works best at higher pH.

Summary Table: Types of Metabolic Pathways

Summary Table: Enzyme Inhibition

Summary Table: Environmental Effects on Enzymes

Additional info: The notes have been expanded with academic context and examples for clarity and completeness.