Chapter 4: A Tour of the Cell

Microscopy and Cell Theory

This section covers the principles of microscopy, cell theory, and the differences between prokaryotic and eukaryotic cells.

• Light Microscope: Uses visible light to magnify specimens up to about 1000x. Maximum magnification is typically 1000-1500x.

• Magnification: The process of enlarging the appearance of an object.

• Resolution: The ability to distinguish two close objects as separate; higher resolution reveals more detail.

• Electron Microscope: Uses electron beams for much higher magnification (up to 1,000,000x) and resolution than light microscopes.

• SEM vs. TEM: Scanning Electron Microscope (SEM) provides 3D surface images; Transmission Electron Microscope (TEM) provides detailed internal structures.

• Cell Theory: All living things are composed of cells; cells are the basic unit of life; all cells come from pre-existing cells.

Cell Structure and Function

Cells have specialized structures (organelles) that perform distinct functions. The structure of the plasma membrane and the types of molecules it contains are essential for cell function.

• Plasma Membrane: A selectively permeable barrier composed mainly of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

• Functions of Membrane Proteins: Transport, signal transduction, cell recognition, enzymatic activity, intercellular joining, and attachment to the cytoskeleton and extracellular matrix.

• Prokaryotic vs. Eukaryotic Cells: Prokaryotes (e.g., bacteria) lack a nucleus and membrane-bound organelles; eukaryotes (e.g., plants, animals, fungi, protists) have both.

Cellular Structures and Their Functions

Different cell types contain various organelles, each with specific roles.

• Nucleoid: Region in prokaryotes where DNA is located.

• Cell Wall: Rigid structure outside the plasma membrane (found in plants, fungi, bacteria).

• Plasma Membrane: Controls entry and exit of substances.

• Nucleus: Contains genetic material (DNA) in eukaryotes.

• Chromosomes: DNA molecules with associated proteins.

• Nucleolus: Site of ribosome synthesis within the nucleus.

• Ribosomes: Sites of protein synthesis; can be free or bound to the endoplasmic reticulum (ER).

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

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

• Lysosomes: Contain digestive enzymes for breaking down waste.

• Vacuoles: Storage organelles, especially large in plant cells.

• Mitochondria: Site of cellular respiration; produces ATP.

• Chloroplasts: Site of photosynthesis in plant cells.

Comparing Plant and Animal Cells

Plant and animal cells share many organelles but also have unique structures.

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

• Animal Cells: Have lysosomes and centrioles; lack cell walls and chloroplasts.

Cell Junctions and Plasmodesmata

Cells connect and communicate through specialized junctions.

• Types of Animal Cell Junctions: Tight junctions, desmosomes, and gap junctions.

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

Chapter 5: The Working Cell

Membrane Structure and Function

The plasma membrane is a dynamic structure that controls the movement of substances in and out of the cell.

• Fluid Mosaic Model: Describes the membrane as a flexible layer with proteins embedded in or attached to a phospholipid bilayer.

• Cholesterol: Stabilizes membrane fluidity.

• Membrane Proteins: Serve as channels, carriers, receptors, enzymes, anchors, and cell recognition molecules.

Transport Across Membranes

Cells use various mechanisms to move substances across membranes.

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

• Active Transport: Movement against the concentration gradient, requiring energy (usually ATP).

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

• Tonicity: The ability of a solution to cause a cell to gain or lose water (isotonic, hypotonic, hypertonic).

• Endocytosis: Uptake of materials via vesicles (phagocytosis, pinocytosis, receptor-mediated endocytosis).

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

Energy and Metabolism

Cells require energy to perform work, which is managed through metabolic pathways.

• Energy: The capacity to do work; exists as kinetic (motion) or potential (stored) energy.

• Thermodynamics: Study of energy transformations. First Law: Energy cannot be created or destroyed. Second Law: Entropy (disorder) increases.

• Exergonic Reactions: Release energy (e.g., cellular respiration).

• Endergonic Reactions: Require energy input (e.g., photosynthesis).

• ATP (Adenosine Triphosphate): Main energy currency of the cell; composed of adenine, ribose, and three phosphate groups.

• Phosphorylation: Transfer of a phosphate group to a molecule, often activating it.

Enzymes and Metabolic Regulation

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

• Enzyme Structure: Substrate binds to the enzyme's active site, forming an enzyme-substrate complex.

• Enzyme Inhibition: Competitive inhibitors bind to the active site; noncompetitive inhibitors bind elsewhere, changing enzyme shape.

• Feedback Inhibition: End product of a pathway inhibits an earlier step to regulate production.

Chapter 6: How Cells Harvest Chemical Energy

Cellular Respiration Overview

Cellular respiration is the process by which cells extract energy from glucose to produce ATP.

• Purpose: To convert chemical energy in food into usable energy (ATP).

• Summary Equation:

• Stages: Glycolysis, Citric Acid Cycle (Krebs Cycle), and Oxidative Phosphorylation (Electron Transport Chain and Chemiosmosis).

Stages of Cellular Respiration

• Glycolysis: Occurs in the cytoplasm; breaks glucose into two pyruvate molecules; produces ATP and NADH.

• Citric Acid Cycle: Occurs in the mitochondrial matrix; completes the breakdown of glucose; produces ATP, NADH, and FADH2.

• Oxidative Phosphorylation: Occurs in the inner mitochondrial membrane; uses NADH and FADH2 to generate ATP via the electron transport chain and chemiosmosis.

Fermentation

Fermentation is an anaerobic process that allows ATP production without oxygen.

• Lactic Acid Fermentation: Occurs in muscle cells; produces lactic acid.

• Alcohol Fermentation: Occurs in yeast; produces ethanol and CO2.

• Obligate vs. Facultative Anaerobes: Obligate anaerobes cannot survive in oxygen; facultative anaerobes can use oxygen if present.

Metabolic Pathways and Energy Harvesting

• Metabolic Pathway: A series of chemical reactions in a cell.

• Enzymes: Each step is catalyzed by a specific enzyme.

• Energy Yield: Cellular respiration is the most efficient pathway for harvesting energy from glucose.

Alcohol Metabolism

• Alcohol Dehydrogenase: Enzyme responsible for metabolizing alcohol.

• Alcohol Metabolism Rate: Varies by individual; typically about one drink per hour.

• Frequent Urination: Alcohol inhibits antidiuretic hormone (ADH), leading to increased urine production.

Summary Table: Comparison of Prokaryotic and Eukaryotic Cells

Additional info:

• Some explanations and examples were expanded for clarity and completeness.

• Table content inferred from standard biology curriculum.