Chapter 6 – A Tour of the Cell

Key Concepts and Definitions

This chapter introduces the fundamental unit of life—the cell—and explores its diversity, structure, and function.

• Cell: The basic structural and functional unit of all living organisms.

• Unicellular: Organisms composed of a single cell (e.g., Escherichia coli).

• Multicellular: Organisms composed of multiple cells (e.g., humans, plants).

• Organelle: Specialized subunit within a cell that has a specific function (e.g., mitochondria, nucleus).

Prokaryotic vs. Eukaryotic Cells

Cells are classified based on the presence or absence of a nucleus and membrane-bound organelles.

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles; DNA is located in the nucleoid region. Examples: Bacteria, Archaea.

• Eukaryotic Cells: Have a true nucleus and membrane-bound organelles. Examples: Animals, plants, fungi, protists.

Cell Size and Surface Area-to-Volume Ratio

Cells are small because a high surface area-to-volume ratio allows efficient exchange of materials with the environment.

• As cell size increases, volume grows faster than surface area.

• Smaller cells have a greater surface area relative to volume, facilitating diffusion and transport.

Cell Structure Identification and Function

Cells contain various organelles, each with distinct functions. Practice identifying structures and understanding their roles.

• Nucleus: Contains genetic material (DNA); controls cell activities.

• Mitochondria: Site of cellular respiration; produces ATP.

• Endoplasmic Reticulum (ER): Synthesizes proteins (rough ER) and lipids (smooth ER).

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosome: Digests macromolecules and cellular debris.

• Plasma Membrane: Regulates entry and exit of substances.

• Ribosome: Synthesizes proteins.

• Cytoskeleton: Provides structural support and facilitates movement.

Structures Shared by Animal and Bacterial Cells

• Plasma membrane

• Cytoplasm

• Ribosomes

• DNA (genetic material)

Endomembrane System and Protein Secretion Pathway

The endomembrane system coordinates the synthesis, modification, and transport of proteins and lipids.

• Includes: Nuclear envelope, ER, Golgi apparatus, lysosomes, vesicles, plasma membrane.

• Pathway: DNA (nucleus) → mRNA → ribosome (rough ER) → protein synthesis → transport vesicle → Golgi apparatus → secretory vesicle → plasma membrane (exocytosis).

Mitochondria and Chloroplasts

• Mitochondria: Double-membraned organelle; site of aerobic respiration and ATP production.

• Chloroplasts: Found in plants and algae; site of photosynthesis.

Cell Walls vs. Extracellular Matrix (ECM)

• Cell Wall: Rigid structure outside the plasma membrane; found in plants, fungi, and bacteria; provides support and protection.

• Extracellular Matrix (ECM): Network of proteins and carbohydrates outside animal cells; provides structural support and regulates cell behavior.

Chapter 7 – Membrane Structure & Function

Phospholipids and Membrane Structure

Biological membranes are primarily composed of phospholipids arranged in a bilayer.

• Phospholipid: Molecule with a hydrophilic (water-loving) head and hydrophobic (water-fearing) tails.

• Bilayer forms the basic structure of cell membranes, creating a semi-permeable barrier.

Membrane Fluidity

• Fluidity is influenced by fatty acid composition and cholesterol content.

• Unsaturated fatty acids increase fluidity; saturated fatty acids decrease fluidity.

• Cholesterol stabilizes membrane fluidity, preventing extremes.

Selective Permeability and Concentration Gradients

• Selective Permeability: Membranes allow certain substances to pass while restricting others.

• Concentration Gradient: Difference in concentration of a substance across a space or membrane.

Passive vs. Active Transport

• Passive Transport: Movement of substances down their concentration gradient without energy input (e.g., diffusion, osmosis).

• Active Transport: Movement of substances against their concentration gradient, requiring energy (ATP).

Osmosis and Water Movement

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Water moves from areas of low solute concentration to high solute concentration.

Types of Membrane Transport

Endocytosis vs. Exocytosis

• Endocytosis: Process by which cells take in materials by engulfing them in vesicles.

• Exocytosis: Process by which cells expel materials in vesicles that fuse with the plasma membrane.

Chapter 8 – Metabolism and Enzymes

Metabolism and Metabolic Pathways

Metabolism encompasses all chemical reactions in a cell, organized into metabolic pathways.

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

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

ATP and Energy Coupling

• ATP (Adenosine Triphosphate): Main energy currency of the cell.

• Energy coupling uses exergonic reactions to drive endergonic reactions via ATP hydrolysis.

Enzymes: Function and Regulation

• Enzyme: Biological catalyst that speeds up chemical reactions by lowering activation energy.

• Active Site: Region on the enzyme where substrate binds.

• Allosteric Site: Site other than the active site that can regulate enzyme activity.

• Feedback Inhibition: End product of a pathway inhibits an earlier step, regulating the pathway.

Exergonic vs. Endergonic Reactions

Thermodynamics in Biology

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

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

Enzyme Activity and Environmental Factors

• Enzyme activity is affected by temperature and pH; each enzyme has optimal conditions.

• Extreme conditions can denature enzymes, reducing activity.

Cellular Control of Metabolism

• Cells regulate metabolism through enzyme activity, compartmentalization, and feedback mechanisms.

Additional info: Some content and examples were expanded for clarity and completeness.