Chapter 4: A Tour of the Cell

Basic Features Shared by All Cells

All cells, regardless of type, share several fundamental structures that are essential for life.

• Plasma Membrane: A selectively permeable barrier that encloses the cell, regulating the movement of substances in and out.

• Cytoplasm: The internal fluid of the cell, containing organelles and the cytosol.

• DNA/RNA: Genetic material responsible for storing and transmitting hereditary information.

• Ribosomes: Molecular machines that synthesize proteins by translating messenger RNA.

Eukaryotic Cellular Parts and Their Functions

Eukaryotic cells contain specialized organelles, each with distinct functions.

• Cell Wall: Provides structural support and protection (found in plants, fungi, and some protists).

• Cytoskeleton: Network of protein filaments (microfilaments, intermediate filaments, microtubules) that maintain cell shape, enable movement, and organize organelles.

• Cilia: Short, hair-like structures for movement or sensory functions.

• Flagella: Long, whip-like structures for cell locomotion.

• Nucleus: Contains genetic material; includes nuclear envelope, chromatin/chromosomes, and nucleolus (site of ribosome synthesis).

• Ribosome: Site of protein synthesis.

• Endoplasmic Reticulum (ER): Rough ER (with ribosomes) synthesizes proteins; Smooth ER synthesizes lipids and detoxifies chemicals.

• Vesicle: Small membrane-bound sacs for transport and storage.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosome: Contains digestive enzymes for breaking down macromolecules.

• Peroxisome: Breaks down fatty acids and detoxifies harmful substances.

• Vacuole: Storage organelle; types include food, central (plants), and contractile (protists).

• Mitochondria: Site of aerobic cellular respiration and ATP production.

• Chloroplast: Site of photosynthesis in plant cells.

Distinguishing Plant Cells from Animal Cells

• Plant Cells: Have cell walls, chloroplasts, and large central vacuoles.

• Animal Cells: Lack cell walls and chloroplasts; may have small vacuoles.

Prokaryotic Cellular Parts

Prokaryotic cells lack membrane-bound organelles and have unique structures.

• Plasma Membrane: Controls entry and exit of substances.

• Slime Layer (Capsule): Provides protection and helps in adhesion.

• Fimbriae: Hair-like appendages for attachment.

• Plasmid (DNA): Small, circular DNA molecules for genetic exchange.

• Ribosomes: Protein synthesis (smaller than eukaryotic ribosomes).

• Cell Wall: Structural support and protection.

• Flagellum: Motility.

• Cytoplasm: Internal fluid.

• Nucleoid Region: Area containing the main DNA.

Distinguishing Prokaryotic from Eukaryotic Cells

• Prokaryotic Cells: No nucleus, no membrane-bound organelles, smaller size.

• Eukaryotic Cells: Nucleus present, membrane-bound organelles, larger size.

Types of Cellular Connections

• Anchoring Junctions: Attach cells to each other or to the extracellular matrix.

• Gap Junctions: Allow direct communication between cells via channels.

• Tight Junctions: Seal cells together to prevent leakage.

• Plasmodesmata: Channels between plant cells for transport and communication.

Chapter 5: The Working Cell

Major Functions of the Cell Membrane

The cell membrane is essential for maintaining cellular integrity and regulating interactions with the environment.

• Barrier: Separates internal cell environment from external surroundings.

• Selective Permeability: Controls which substances can enter or leave the cell.

• Communication: Contains proteins for signaling and interaction with other cells.

• Transport: Facilitates movement of molecules via proteins.

Selective Permeability of the Cell Membrane

The cell membrane allows certain molecules to pass while restricting others, based on size, charge, and solubility.

• Small, nonpolar molecules: Pass easily (e.g., O2, CO2).

• Large or charged molecules: Require transport proteins.

Fluid Mosaic Model Components

The fluid mosaic model describes the structure of the cell membrane as a dynamic combination of lipids and proteins.

• Phospholipids: Form a bilayer with hydrophobic (water-repelling) tails and hydrophilic (water-attracting) heads.

• Transport Proteins: Facilitate movement of substances across the membrane.

• Receptor Proteins: Receive and transmit signals from the environment.

• Enzymes: Catalyze reactions at the membrane surface.

• Glycoproteins: Proteins with carbohydrate chains for cell recognition.

• Attachment Proteins: Anchor the membrane to the cytoskeleton or extracellular matrix.

Key Terms and Concepts

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

• Diffusion: Movement of molecules from high to low concentration.

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

• Solvent: Substance in which solutes are dissolved (e.g., water).

• Solute: Substance dissolved in a solvent.

• Passive Transport: Movement without energy input (e.g., diffusion, osmosis).

• Active Transport: Movement against concentration gradient, requires energy (ATP).

• Simple Diffusion: Direct movement through the membrane.

• Facilitated Diffusion: Movement via transport proteins.

• Exocytosis: Export of materials via vesicles.

• Endocytosis: Import of materials via vesicles.

• Phagocytosis: "Cell eating"; uptake of large particles.

• Pinocytosis: "Cell drinking"; uptake of fluids.

• Receptor-Mediated Endocytosis: Uptake of specific molecules via receptor binding.

• Carrier Proteins: Bind and transport specific molecules.

• Channel Proteins: Form pores for passive movement.

• Aquaporins: Channel proteins specifically for water transport.

Effects of Tonicity on Cells

Tonicity describes the effect of solute concentration on cell volume.

• Hypotonic Solution: Lower solute concentration outside; cell gains water and may burst.

• Isotonic Solution: Equal solute concentration; cell maintains normal shape.

• Hypertonic Solution: Higher solute concentration outside; cell loses water and shrinks.

Chapter 6: How Cells Harvest Chemical Energy

Photosynthesis vs. Aerobic Cellular Respiration

These two processes are central to energy flow in biological systems.

Equations:

• Photosynthesis:

• Aerobic Respiration:

Glucose Metabolism and ATP Formation

Glucose is a primary energy source; its breakdown releases energy used to form ATP, the cell's energy currency.

• ATP: Adenosine triphosphate; stores and transfers energy for cellular processes.

Glycolysis

Glycolysis is the first step in cellular respiration, occurring in the cytoplasm.

• Location: Cytoplasm

• End Products: 2 pyruvate, 2 ATP, 2 NADH

Aerobic Cellular Respiration Steps

• Pyruvate Oxidation: Pyruvate enters mitochondria; converted to acetyl-CoA, producing NADH and CO2.

• Krebs Cycle (Citric Acid Cycle): Produces NADH, FADH2, and ATP.

• Electron Transport Chain: NADH and FADH2 donate electrons; energy used to pump protons.

• Oxidative Phosphorylation (Chemiosmosis): Protons flow back through ATP synthase, generating ATP.

Role of O2: Final electron acceptor in the electron transport chain; essential for ATP production.

Chapter 7: Photosynthesis: Using Light to Make Food

Autotrophs vs. Heterotrophs

Organisms are classified based on how they obtain nutrition.

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

• Heterotrophs (Consumers): Obtain food by consuming other organisms.

Photosynthesis Equation

The overall chemical reaction for photosynthesis is:

Structure and Function of Chloroplast

• Stroma: Fluid-filled space where the Calvin cycle occurs.

• Thylakoid: Membrane-bound sacs containing chlorophyll; site of light reactions.

• Granum: Stack of thylakoids.

Role of Chlorophyll

Chlorophyll is the pigment that absorbs light energy, initiating photosynthesis.

• Absorbs: Blue and red wavelengths; reflects green.

Light Reactions vs. Calvin Cycle

• Light Reactions: Convert light energy to chemical energy (ATP, NADPH); release O2.

• Calvin Cycle: Uses ATP and NADPH to fix CO2 into glucose.