Chapter 8: Introduction to Metabolism and Enzymes

Key Concepts in Metabolism

Metabolism encompasses all chemical reactions that occur within living organisms to maintain life. These reactions are organized into metabolic pathways, which can be classified as either anabolic or catabolic.

• Anabolic Pathway: A series of reactions that build complex molecules from simpler ones, requiring energy input (e.g., synthesis of proteins from amino acids).

• Catabolic Pathway: A series of reactions that break down complex molecules into simpler ones, releasing energy (e.g., cellular respiration).

• Kinetic Energy: Energy associated with motion.

• Potential Energy: Stored energy due to position or structure.

• Chemical Energy: Potential energy stored in chemical bonds.

• Entropy (S): A measure of disorder or randomness in a system.

• Exergonic Reaction: A reaction that releases energy; spontaneous.

• Endergonic Reaction: A reaction that requires energy input; nonspontaneous.

• Energy Coupling: The use of energy released from exergonic reactions to drive endergonic reactions.

Thermodynamics in Biology

Thermodynamics governs energy transformations in biological systems. The first and second laws are especially relevant.

• First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.

• Second Law of Thermodynamics: Every energy transfer increases the entropy of the universe.

• Open System: Exchanges energy and matter with surroundings (e.g., living cells).

• Closed System: Isolated from surroundings; no exchange of energy or matter.

Free Energy and Spontaneity

Free energy (Gibbs free energy) determines whether a reaction is spontaneous.

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

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

• Spontaneous Reaction: Occurs without energy input ().

• Nonspontaneous Reaction: Requires energy input ().

ATP and Cellular Work

ATP (adenosine triphosphate) is the primary energy currency of the cell, driving cellular work through energy coupling.

• ATP Structure: Adenine base, ribose sugar, and three phosphate groups.

• ATP Hydrolysis: Releases energy by breaking the terminal phosphate bond.

• Energy Coupling: ATP hydrolysis powers endergonic reactions.

Enzymes and Activation Energy

Enzymes are biological catalysts that lower activation energy, increasing the rate of chemical reactions.

• Substrate: The reactant an enzyme acts upon.

• Active Site: The region of the enzyme where the substrate binds.

• Induced Fit: The enzyme changes shape to better fit the substrate.

• Cofactors and Coenzymes: Non-protein helpers required for enzyme activity.

• Competitive Inhibitor: Binds to the active site, blocking substrate binding.

• Noncompetitive Inhibitor: Binds elsewhere, altering enzyme shape and function.

• Allosteric Regulation: Regulation of enzyme activity by binding of molecules at sites other than the active site.

Chapter 9: Cellular Respiration and Fermentation

Overview of Cellular Respiration

Cellular respiration is a catabolic pathway that breaks down glucose to produce ATP, using oxygen in aerobic conditions.

• Balanced Equation:

• Stages: Glycolysis, Pyruvate Oxidation, Citric Acid Cycle, Electron Transport Chain (ETC).

Redox Reactions in Respiration

Redox reactions involve the transfer of electrons between molecules, crucial for energy extraction in respiration.

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• Reducing Agent: Donates electrons.

• Oxidizing Agent: Accepts electrons.

• NAD+/NADH and FAD/FADH2: Electron carriers in cellular respiration.

Stages and Locations of Cellular Respiration

Each stage of cellular respiration occurs in specific regions of the eukaryotic cell and involves distinct inputs and outputs.

• Glycolysis: Cytoplasm; glucose → pyruvate, ATP, NADH.

• Pyruvate Oxidation: Mitochondrial matrix; pyruvate → acetyl-CoA, CO2, NADH.

• Citric Acid Cycle (Krebs Cycle): Mitochondrial matrix; acetyl-CoA → CO2, ATP, NADH, FADH2.

• Electron Transport Chain: Inner mitochondrial membrane; NADH/FADH2 → ATP, H2O.

ATP Production Mechanisms

ATP is produced by substrate-level phosphorylation and oxidative phosphorylation.

• Substrate-Level Phosphorylation: Direct transfer of phosphate to ADP from a substrate.

• Oxidative Phosphorylation: ATP synthesis powered by the electron transport chain and chemiosmosis.

• ATP Synthase: Enzyme that uses the proton gradient to synthesize ATP from ADP and Pi.

Fermentation and Anaerobic Respiration

When oxygen is unavailable, cells use fermentation or anaerobic respiration to produce ATP.

• Alcohol Fermentation: Pyruvate → ethanol + CO2 + NAD+.

• Lactic Acid Fermentation: Pyruvate → lactate + NAD+.

• Anaerobic Respiration: Uses electron acceptors other than oxygen.

Comparison of ATP Yield

Chapter 10: Photosynthesis

Structure and Function of Chloroplasts

Photosynthesis occurs in chloroplasts, which contain specialized structures for capturing light energy.

• Thylakoids: Membranous sacs where light reactions occur.

• Stroma: Fluid surrounding thylakoids; site of the Calvin cycle.

• Granum: Stack of thylakoids.

Autotrophs vs. Heterotrophs

Organisms are classified based on how they obtain energy and carbon.

• Autotrophs: Produce their own food from inorganic sources (e.g., plants).

• Heterotrophs: Obtain energy by consuming other organisms.

Photosynthetic Pigments and Light Capture

Pigments absorb light energy for photosynthesis.

• Chlorophyll a: Main pigment in photosynthesis.

• Chlorophyll b and Carotenoids: Accessory pigments that broaden the spectrum of absorbed light.

Photosystems and Electron Flow

Photosystems I and II are protein complexes that capture light and transfer electrons.

• Linear Electron Flow: Produces ATP and NADPH.

• Cyclic Electron Flow: Produces ATP only.

ATP and NADPH in the Calvin Cycle

ATP and NADPH generated in the light reactions are used in the Calvin cycle to fix carbon dioxide into sugars.

• Calvin Cycle: Series of reactions that convert CO2 into glucose.

Photorespiration and Adaptations

Photorespiration is a process that reduces the efficiency of photosynthesis, especially under hot, dry conditions. Plants have evolved adaptations to minimize photorespiration.

• C3 Plants: Use the Calvin cycle directly; susceptible to photorespiration.

• C4 Plants: Minimize photorespiration by spatial separation of steps.

• CAM Plants: Minimize photorespiration by temporal separation of steps.

Chapter 11: Cell Communication and Signaling

Principles of Cell Signaling

Cells communicate using chemical signals, which can be local or long-distance.

• Local Signaling: Paracrine (nearby cells), Synaptic (neurons).

• Endocrine Signaling: Hormones travel through the bloodstream to distant cells.

Stages of Cell Signaling

Cell signaling involves three main stages: reception, transduction, and response.

• Reception: Signal molecule binds to receptor.

• Transduction: Signal is relayed and amplified through a cascade of molecular events.

• Response: The cell carries out a specific activity.

Signal Transduction Pathways

Signal transduction often involves second messengers and protein phosphorylation cascades.

• G Protein-Coupled Receptors (GPCRs): Transmit signals via G proteins.

• Second Messengers: Small molecules like cAMP that relay signals inside the cell.

• Phosphorylation Cascade: Series of protein kinases activating each other.

• Scaffolding Proteins: Organize signaling complexes for efficiency.

Apoptosis and Signal Integration

Apoptosis is programmed cell death, regulated by complex signaling pathways.

• Apoptosis: Eliminates damaged or unnecessary cells.

• Integration of Pathways: Multiple signals can converge to regulate apoptosis.

Additional info: Some definitions and explanations were expanded for clarity and completeness. Table entries for ATP yield are based on standard biological knowledge.