chapter 8 metabolism

Introduction to Metabolism

• Metabolism refers to the totality of an organism's chemical reactions.

• It is considered an emergent property of life, arising from orderly interactions between molecules.

Metabolic Pathways

• A metabolic pathway begins with a specific molecule and ends with a product.

• Each step of the pathway is facilitated by a specific enzyme.

  • Example: Enzyme 1 catalyzes the conversion of a starting molecule A to product B through Reaction 1, with subsequent enzymes carrying out further reactions until product D is formed.

Types of Metabolism

Catabolic Pathways

• Catabolic pathways are metabolic routes that release energy by breaking down complex molecules into simpler compounds.

  • Example: Cellular respiration converts glucose and oxygen into carbon dioxide, water, and energy (ATP).

Anabolic Pathways

• Anabolic pathways consume energy to construct complex molecules from simpler ones.

  • Example: Photosynthesis utilizes light energy to convert carbon dioxide and water into glucose.

Energy Basics

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

  • Kinetic Energy: Associated with motion.

  • Potential Energy: Related to an object's location or structure.

Laws of Thermodynamics

First Law of Thermodynamics

• Energy is conserved; it cannot be created or destroyed, only transformed or transferred.

Second Law of Thermodynamics

• Every energy transfer increases the entropy (disorder) of the universe, indicating that systems naturally progress towards a state of greater disorder.

• Entropy is a measure of molecular disorder.

Spontaneity of Processes

• Spontaneous processes occur without energy input and increase the universe's entropy.

• Nonspontaneous processes require energy to occur because they decrease entropy.

Free Energy Concepts

Free Energy (ΔG)

• Free energy (G) is the energy that can do work in a system at uniform temperature and pressure.

• A living system's free energy indicates its stability: higher free energy means less stability and more work capacity.

  • Spontaneous processes: ΔG < 0 (free energy decreases).

  • Nonspontaneous processes: ΔG ≥ 0 (free energy does not decrease).

Equilibrium

• Equilibrium signifies maximum stability, with processes only able to perform work while moving towards this state.

Types of Chemical Reactions

Exergonic Reactions

• Exergonic reactions are spontaneous and release free energy (ΔG < 0).

Endergonic Reactions

• Endergonic reactions absorb free energy and are nonspontaneous (ΔG > 0).

Work Performed by Cells

• Cells perform three main types of work:

  • Chemical work: Synthesizing complex molecules from simpler ones (endergonic reactions).

  • Transport work: Pumping substances across membranes against their natural flow (active transport).

  • Mechanical work: Muscle contraction and cell motility.

Energy Coupling

• Cells manage energy through energy coupling, where an exergonic process drives an endergonic one.

• Most energy coupling in cells occurs via ATP (adenosine triphosphate).

Structure and Function of ATP

• ATP consists of ribose, adenine, and three phosphate groups.

• Hydrolysis of ATP releases energy that can be harnessed to perform cellular work.

Enzyme Functionality

Catalysts and Enzymes

• Catalysts speed up reactions without being consumed; enzymes are biological catalysts.

  • Example: Sucrase catalyzes the breakdown of sucrose.

Mechanism of Enzymes

• Enzymes lower activation energy (EA), which is necessary for a reaction to occur.

• The active site of the enzyme binds substrates and facilitates the conversion to products.

Enzyme Activity Regulation

• The rate of enzyme-catalyzed reactions can be influenced by substrate concentration and the saturation of active sites.

• Enzymes function optimally under specific conditions.

• Cofactors (nonprotein helpers) and coenzymes (organic cofactors) assist enzyme activity.

Inhibition of Enzyme Activity

• Enzyme activity can be inhibited through:

  • Competitive inhibition: Inhibitors compete with substrates for the active site.

  • Noncompetitive inhibition: Inhibitors bind to the enzyme, causing a change in shape and reducing activity.

• Feedback inhibition: The end product of a reaction inhibits an earlier step, regulating production and resource allocation.

Free Energy and Stability

• Free energy indicates a system's tendency to change towards a more stable state.

• The equation: ΔG = ΔH - TΔS relates free energy change (ΔG) to changes in enthalpy (ΔH) and entropy (ΔS).

These notes encompass the detailed discussion of metabolism, energy types, enzyme activity, and metabolic pathways, which are foundational concepts in biochemistry.