Chapter 6: Cell Structure and Microscopy

Microscopy and Cell Components

This topic introduces the tools and concepts used to study cells, including different types of microscopes and the major organelles found in eukaryotic and prokaryotic cells.

• Light vs. Electron Microscopes: Light microscopes use visible light to magnify specimens, while electron microscopes use electron beams for higher resolution. Advantages/Disadvantages: Electron microscopes provide greater detail but require more complex sample preparation and cannot view living cells.

• Scanning vs. Transmission Electron Microscopes: Scanning electron microscopes (SEM) provide 3D images of surfaces; transmission electron microscopes (TEM) show internal structures.

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

• Limits to Cell Size: Cell size is limited by surface area-to-volume ratio, affecting nutrient uptake and waste removal.

• Prokaryotic vs. Eukaryotic Cells: Prokaryotes lack membrane-bound organelles and a nucleus; eukaryotes possess these structures.

• Structure and Function of Organelles: Key organelles include the nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, and cytoskeleton.

• Endomembrane System: A network of membranes within eukaryotic cells involved in synthesis, transport, and modification of cellular products.

• Ribosomes: Sites of protein synthesis, found in both prokaryotic and eukaryotic cells.

• Differences Between Plant and Animal Cells: Plant cells have cell walls, chloroplasts, and large central vacuoles; animal cells do not.

• Cytoskeleton: Provides structural support, motility, and regulation. Main components include microtubules, microfilaments, and intermediate filaments.

Example: The Golgi apparatus modifies and packages proteins for secretion or delivery to other organelles.

Chapter 7: Membrane Structure and Transport

Fluid Mosaic Model and Membrane Function

This topic covers the structure of biological membranes and the mechanisms by which substances move across them.

• Fluid Mosaic Model: Describes the plasma membrane as a dynamic structure with proteins floating in or on a fluid lipid bilayer.

• Plasma Membrane Components: Includes phospholipids, cholesterol, integral and peripheral proteins, and carbohydrates.

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

• Transport Proteins: Facilitate movement of ions and molecules across membranes via channels and carriers.

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

• Active Transport: Movement against a concentration gradient, requiring energy (usually ATP). Additional info: This equation is more relevant to chemistry; in biology, active transport rate depends on ATP availability and transporter kinetics.

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

• Isotonic, Hypotonic, Hypertonic Solutions: Affect water movement in and out of cells, impacting cell volume.

• Aquaporins: Channel proteins that facilitate rapid water transport.

• Sodium-Potassium Pump: Maintains electrochemical gradients by pumping Na+ out and K+ into cells. per ATP hydrolyzed.

• Endocytosis and Exocytosis: Bulk transport mechanisms for large molecules or particles.

Example: Red blood cells placed in a hypotonic solution will swell due to water influx.

Chapter 8: Cellular Energetics and Enzymes

Thermodynamics and Metabolism

This topic explores the principles of energy transformation in cells, including metabolic pathways and enzyme function.

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

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

• Free Energy Equation: Where is change in free energy, is change in enthalpy, is temperature in Kelvin, and is change in entropy.

• ATP: The primary energy currency of the cell, used to drive endergonic reactions.

• Enzyme Function: Enzymes are biological catalysts that lower activation energy and increase reaction rates.

• Enzyme Inhibition: Can be competitive (inhibitor binds active site) or noncompetitive (inhibitor binds elsewhere).

• Environmental Effects: Temperature and pH can affect enzyme activity.

• Regulation: Allosteric regulation and feedback inhibition control metabolic pathways.

Example: The enzyme hexokinase catalyzes the phosphorylation of glucose in glycolysis.

Chapter 9: Cellular Respiration and Fermentation

Energy Production in Cells

This topic describes how cells extract energy from organic molecules through aerobic respiration and fermentation.

• Oxidation of Organic Fuel: Cellular respiration involves the breakdown of glucose and other fuels to produce ATP.

• Three Main Stages: Glycolysis, Citric Acid Cycle (Krebs Cycle), and Oxidative Phosphorylation.

• Fermentation: Occurs in the absence of oxygen, regenerates NAD+ for glycolysis.

• Electron Transport Chain (ETC): Series of protein complexes in the mitochondrial membrane that transfer electrons and pump protons to create a proton gradient.

• ATP Synthesis: Driven by chemiosmosis and the proton-motive force.

• Substrate-Level vs. Oxidative Phosphorylation: Substrate-level phosphorylation directly transfers a phosphate group to ADP; oxidative phosphorylation uses the ETC and ATP synthase.

• NAD+ Recycling: Essential for continued glycolysis and energy production.

Example: During aerobic respiration, one molecule of glucose can yield up to 32 molecules of ATP.

Major Processes in Cellular Respiration

Additional info: The table summarizes the main steps, locations, and outputs of cellular respiration and fermentation for exam review.