Cell Structure and Function

CH 6: The Cell

This section covers the fundamental concepts of cell biology, including cell theory, cell types, organelles, and cellular structures. Understanding these topics is essential for grasping how living organisms function at the microscopic level.

• Cell Theory: States that all living things are composed of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells.

• Cell Size: Cells are small to maximize surface area-to-volume ratio, facilitating efficient exchange of materials with their environment.

• Common Features of All Cells: All cells have a plasma membrane, cytoplasm, DNA, and ribosomes.

• Prokaryotic vs. Eukaryotic Cells:

  • Prokaryotic cells (e.g., Bacteria, Archaea) lack a nucleus and membrane-bound organelles.

  • Eukaryotic cells (e.g., Plants, Animals, Fungi, Protists) have a nucleus and membrane-bound organelles.

  • Example: Escherichia coli (prokaryote) vs. Homo sapiens skin cell (eukaryote).

• Plant vs. Animal Cells:

  • Plant cells have cell walls, chloroplasts, and large central vacuoles.

  • Animal cells lack cell walls and chloroplasts but have centrioles and lysosomes.

• Cell Walls:

  • Bacterial cell walls are made of peptidoglycan.

  • Plant cell walls are composed of cellulose.

• Major Regions of Eukaryotic Cells:

  • Nucleus

  • Cytoplasm

  • Plasma membrane

• Endomembrane System: A network of membranes inside eukaryotic cells, including the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, and vesicles.

• Functions of Eukaryotic Organelles:

  • Nucleus: Stores genetic information.

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

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

  • Lysosomes: Digestive organelles.

  • Vacuoles: Storage and structural support (especially in plants).

• Mitochondria and Chloroplasts:

  • Mitochondria: Site of cellular respiration, producing ATP.

  • Chloroplasts: Site of photosynthesis in plants and algae.

• Endosymbiosis: Theory that mitochondria and chloroplasts originated as free-living prokaryotes engulfed by ancestral eukaryotic cells.

• Cytoskeleton and Extracellular Matrix (ECM):

  • Cytoskeleton: Network of protein fibers (microtubules, microfilaments, intermediate filaments) providing structural support and facilitating movement.

  • ECM: Network of proteins and carbohydrates outside animal cells, providing support and signaling.

• Cell Junctions:

  • Tight junctions: Seal cells together.

  • Desmosomes: Anchor cells to each other.

  • Gap junctions: Allow communication between cells.

• Labeling Cell Parts: Be able to identify and label organelles and structures in diagrams or micrographs.

CH 7: Membrane Structure and Function

This section explores the structure and function of biological membranes, focusing on the plasma membrane, membrane proteins, and transport mechanisms.

• Plasma Membrane Anatomy: Composed of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

• Phospholipid Structure: Each phospholipid has a hydrophilic (water-attracting) head and two hydrophobic (water-repelling) tails.

• Bilayer Arrangement: Phospholipids form a bilayer with heads facing outward toward water and tails facing inward, away from water.

• Membrane Proteins:

  • Integral proteins: Span the membrane.

  • Peripheral proteins: Attached to the membrane surface.

  • Proteins serve as channels, carriers, receptors, enzymes, and anchors.

• Labeling Membrane Structures: Be able to identify phospholipids, proteins, and other components in diagrams.

• Passive vs. Active Transport:

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

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

• Osmosis and Tonicity:

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

  • Hypotonic solution: Lower solute concentration outside the cell; water enters the cell.

  • Hypertonic solution: Higher solute concentration outside the cell; water leaves the cell.

  • Isotonic solution: Equal solute concentration; no net water movement.

• Osmotic Effects on Plant and Animal Cells:

  • Plant cells become turgid in hypotonic solutions and plasmolyzed in hypertonic solutions.

  • Animal cells may burst (lyse) in hypotonic solutions or shrink (crenate) in hypertonic solutions.

• Bulk Transport Mechanisms:

  • Endocytosis: Uptake of materials into the cell via vesicles.

  • Phagocytosis: "Cell eating"; engulfing large particles.

  • Pinocytosis: "Cell drinking"; uptake of fluids and dissolved substances.

  • Exocytosis: Release of materials from the cell via vesicles.

• Comparison Table: Types of Membrane Transport

Key Equations

• Surface Area to Volume Ratio:

• Osmotic Pressure (van't Hoff equation):

Where is osmotic pressure, is the ionization constant, is molarity, is the gas constant, and is temperature in Kelvin.

Example: In a hypotonic solution, a plant cell will swell as water enters by osmosis, becoming turgid and supporting the plant's structure.