Overview
This lecture reviews the cytoplasm and cellular organelles, focusing on the endomembrane system, energy-related organelles, and the structure and function of the cytoskeleton.
The Cytoplasm and Organelles
- The cytoplasm includes cytosol (jelly-like fluid) and organelles, excluding the nucleus.
- Organelles are specialized membrane-bound structures with specific cellular functions.
- The nucleus houses DNA and serves as the cell's control center.
Endomembrane System
- The endomembrane system includes the endoplasmic reticulum (ER), Golgi apparatus, and vesicles.
- Rough ER has ribosomes; synthesizes and modifies proteins for membranes or export.
- Smooth ER lacks ribosomes; synthesizes lipids, stores Ca++, metabolizes carbs, and detoxifies toxins.
- The Golgi apparatus sorts, modifies, and packages molecules from the ER for transport or export.
- Lysosomes are enzyme-filled organelles that digest cellular waste, damaged organelles, or foreign particles; involved in autophagy and apoptosis.
Energy Production and Detoxification Organelles
- Mitochondria are double-membraned, bean-shaped organelles where ATP is produced from nutrients via cellular respiration.
- Mitochondria have inner membrane folds (cristae) that increase surface area for energy reactions.
- Peroxisomes contain enzymes for lipid metabolism and detoxification, neutralizing reactive oxygen species (ROS) and breaking down toxins like alcohol.
Reactive Oxygen Species and Aging
- ROS (e.g., hydrogen peroxide, free radicals) are byproducts of metabolism that can damage DNA, proteins, and cell membranes.
- Peroxisomes neutralize ROS, but excessive ROS causes oxidative stress, linked to aging and diseases.
- The free radical theory of aging suggests oxidative stress contributes to aging and age-related diseases.
The Cytoskeleton
- The cytoskeleton is a network of protein filaments providing structural support, cell movement, and transport.
- Microtubules (thickest) are made of tubulin and maintain cell shape, position organelles, and form cilia/flagella.
- Microfilaments (thinnest) are composed of actin, provide support, and enable muscle contraction and cell division.
- Intermediate filaments (keratin-based) resist tension, maintain cell shape, and anchor organelles.
Key Terms & Definitions
- Organelle — membrane-bound structure with specialized cellular function.
- Endomembrane system — interconnected organelles (ER, Golgi, vesicles) for molecule processing and transport.
- Endoplasmic Reticulum (ER) — network for synthesis and transport (rough: protein; smooth: lipid, detoxification).
- Golgi apparatus — modifies, sorts, and ships cell products.
- Lysosome — digests cellular waste and foreign material.
- Mitochondrion — powerhouse of the cell, producing ATP via cellular respiration.
- Peroxisome — detoxifies harmful substances and decomposes ROS.
- Reactive Oxygen Species (ROS) — highly reactive molecules causing oxidative damage.
- Cytoskeleton — internal protein scaffold (microtubules, microfilaments, intermediate filaments).
- Microtubule — thick, tubulin-based cytoskeletal component for structure and transport.
- Microfilament — actin-based, thin filament for movement and division.
- Intermediate filament — keratin-based, medium-thick filament providing tensile strength.
Action Items / Next Steps
- Watch the suggested video on the endomembrane system.
- Review diagrams of cell structure and organelles.
- Study the functions and features of each organelle for upcoming assessments.