Metabolism and Thermodynamics

Overview of Metabolism

Metabolism refers to all chemical reactions that occur within an organism to maintain life. These reactions transform energy and matter, enabling growth, reproduction, and cellular maintenance.

• Catabolic Pathways: Break down complex molecules into simpler ones, releasing energy (e.g., cellular respiration).

• Anabolic Pathways: Build complex molecules from simpler ones, consuming energy (e.g., protein synthesis).

Forms of Energy

• Kinetic Energy: Energy of motion; e.g., movement of molecules.

• Potential Energy: Stored energy due to position or structure; e.g., chemical bonds.

Laws of Thermodynamics

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

• Second Law: Every energy transfer increases the entropy (disorder) of the universe.

• Total Laws: Two main laws relevant to biology.

Spontaneity and Free Energy

• Spontaneous Reaction: Occurs without input of energy; determined by free energy change ().

• Gibbs Free Energy Equation:

• : Change in free energy

• : Change in enthalpy (total energy)

• : Temperature in Kelvin

• : Change in entropy

Exergonic vs. Endergonic Reactions

• Exergonic: ; releases energy; spontaneous.

• Endergonic: ; requires energy input; non-spontaneous.

ATP and Coupled Reactions

• ATP (Adenosine Triphosphate): Main energy currency of the cell; powers cellular work by transferring a phosphate group.

• Coupled Reactions: Energy released from exergonic reactions is used to drive endergonic reactions.

Enzymes and Metabolic Regulation

Enzyme Function and Structure

Enzymes are biological catalysts that speed up metabolic reactions by lowering activation energy.

• Active Site: Region on enzyme where substrate binds.

• Induced Fit Model: Enzyme changes shape to fit substrate more closely upon binding.

• Specificity: Determined by enzyme structure; only specific substrates fit the active site.

Enzyme Activity and Regulation

• Activation Energy: Energy required to start a reaction; enzymes lower this barrier.

• Enzyme Inhibitors: Molecules that decrease enzyme activity (competitive or noncompetitive).

• Regulation: Ensures metabolic pathways are controlled and efficient.

Metabolic Pathway Regulation

• Feedback Inhibition: End product inhibits an earlier step in the pathway.

• Allosteric Regulation: Enzyme activity is modified by binding of regulatory molecules at sites other than the active site.

Energy Diagrams

Energy diagrams illustrate the change in free energy during reactions, showing activation energy and overall energy change.

Redox Reactions and Cellular Respiration

Oxidation and Reduction

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• Redox Reaction: Transfer of electrons between molecules; essential for energy exchanges in cells.

Phosphorylation

• Substrate-level Phosphorylation: Direct transfer of phosphate to ADP to form ATP.

• Oxidative Phosphorylation: ATP formation driven by electron transport chain and chemiosmosis.

Cellular Respiration Overview

• Reactants: Glucose and oxygen.

• Products: Carbon dioxide, water, and ATP.

• Location: Mitochondria (mainly).

• Electron Transport Chain: Transfers electrons, creates proton gradient for ATP synthesis.

Glycolysis

• Location: Cytoplasm.

• Phases: Energy investment and energy payoff.

• Reactants: Glucose, ATP.

• Products: Pyruvate, NADH, ATP.

Citric Acid Cycle (Krebs Cycle)

• Location: Mitochondrial matrix.

• Reactants: Acetyl-CoA, NAD+, FAD.

• Products: CO2, NADH, FADH2, ATP.

• Purpose: Completes glucose oxidation, produces electron carriers.

Oxidative Phosphorylation

• Electron Transport Chain: Transfers electrons, pumps protons to create gradient.

• Chemiosmosis: ATP synthase uses proton gradient to synthesize ATP.

Inputs and Outputs Table

Fermentation

• Alcohol Fermentation: Pyruvate converted to ethanol and CO2.

• Lactic Acid Fermentation: Pyruvate converted to lactate.

• Purpose: Regenerates NAD+ for glycolysis in absence of oxygen.

Fermentation vs. Cellular Respiration

Cell Division and the Cell Cycle

Purpose and Phases of Cell Division

• Purpose: Growth, repair, reproduction.

• Phases: Interphase (G1, S, G2), Mitosis (Prophase, Metaphase, Anaphase, Telophase), Cytokinesis.

Mitosis

• Prophase: Chromosomes condense, spindle forms.

• Metaphase: Chromosomes align at cell equator.

• Anaphase: Sister chromatids separate.

• Telophase: Nuclear envelope reforms, chromosomes decondense.

Mitotic Spindle

• Definition: Structure made of microtubules that separates chromosomes.

• Attachment: Spindle fibers attach to centromeres via kinetochores.

• Function: Ensures accurate chromosome segregation.

Cytokinesis

• Animal Cells: Cleavage furrow forms.

• Plant Cells: Cell plate forms.

Regulation of Cell Cycle

• Checkpoints: Control progression; prevent uncontrolled division (cancer).

• Regulatory Proteins: Cyclins and cyclin-dependent kinases (CDKs).

Comparison Table: Cell Cycle Phases

Photosynthesis and Related Processes

Chloroplast Structure

• Outer Membrane: Protective layer.

• Inner Membrane: Encloses stroma.

• Stroma: Fluid-filled space; site of Calvin cycle.

• Thylakoid System: Membranous sacs; site of light reactions.

• Grana: Stacks of thylakoids.

• Thylakoid Lumen: Internal space of thylakoid.

Autotrophs vs. Heterotrophs

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

• Heterotrophs: Obtain food from other organisms (e.g., animals).

Photosystems and Photolysis

• Photosystem: Protein complex that absorbs light and initiates electron transfer.

• Photolysis: Splitting of water to provide electrons; produces O2.

Photosynthesis

• Purpose: Convert light energy to chemical energy (glucose).

• Stages: Light reactions (thylakoid), Calvin cycle (stroma).

• Reactants: CO2, H2O, light.

• Products: Glucose, O2.

Aerobic Respiration

• Purpose: Break down glucose to produce ATP.

• Location: Mitochondria.

• Reactants: Glucose, O2.

• Products: CO2, H2O, ATP.

Calvin Cycle

• Purpose: Fix carbon to produce glucose.

• Location: Stroma of chloroplast.

• Reactants: CO2, ATP, NADPH.

• Products: Glucose, ADP, NADP+.

Comparison Table: Photosynthesis vs. Aerobic Respiration

Additional info: These notes expand upon the review questions and diagrams, providing definitions, explanations, and tables for key biological processes relevant to a college-level General Biology course.