Cell Structure Part 2 PDF

# The Endomembrane System The endomembrane system is a network of interacting organelles between the nucleus and plasma membrane. It's responsible for a variety of functions: - Making, modifying, and transporting proteins and lipids for secretion or into cell membranes - Destroying toxins - Recycli...

# The Endomembrane System The endomembrane system is a network of interacting organelles between the nucleus and plasma membrane. It's responsible for a variety of functions: - Making, modifying, and transporting proteins and lipids for secretion or into cell membranes - Destroying toxins - Recycling waste - Other specialized functions ## Components of the endomembrane system - **Nucleus:** Contains the cell's DNA and is surrounded by a nuclear envelope. - **Nuclear Envelope:** Double membrane that surrounds the nucleus, connected to the rough ER. - **Endoplasmic Reticulum (ER):** A continuous, folded compartment extending from the nuclear envelope. It is responsible for protein folding and lipid metabolism. - **Rough ER:** Contains ribosomes that synthesize proteins. - **Smooth ER:** Synthesizes lipids, detoxifies harmful substances, and breaks down carbohydrates. - **Vesicles:** Small membrane-enclosed sacs that store and transport substances. - **Golgi complex:** A folded membrane containing enzymes that further process proteins and lipids produced by the ER. Packages molecules into vesicles for transport to the plasma membrane or lysosomes. - **Lysosomes:** Vesicles containing enzymes that fuse with vacuoles to digest waste materials. - **Peroxisomes:** Vesicles containing enzymes that break down hydrogen peroxide, alcohol, and other toxins. - **Vacuoles:** Varying sizes and functions depending on cell type. - Central vacuole: Occupies 50-90% of a cell's interior and stores amino acids, sugars, ions, wastes, and toxins. - Fluid pressure helps keep plant cells firm. ## Eukaryotic Cells ### Mitochondria A eukaryotic organelle that creates energy (ATP) through aerobic respiration. - Contains two membranes (inner and outer) that create compartments. - Has its own DNA and ribosomes. - Resembles bacteria and may have evolved by endosymbiosis. ## Other organelles - **Plastids:** Involved in photosynthesis or storage. - Chloroplasts: Specialized for photosynthesis. - **Cytoskeleton:** Provides structural support and cell movement. - Microtubules: Long, hollow cylinders made of tubulin. - Microfilaments: Consists primarily of the protein actin. - Intermediate filaments: Maintain cell and tissue structure. - **Motor proteins:** Accessory proteins that move molecules throughout the cell along microtubules and microfilaments. - **Kinesin** moves vesicles towards the plus end of microtubules. ## Interactions between cells - **Cell Junctions:** Allow cells to interact with each other and the environment. - **Plasmodesmata (in plants):** Channels that allow for the passage of molecules between plant cells. - **Tight junctions, adhering junctions, and gap junctions (in animals):** Different structural junctions that hold animal cells together. ## Properties of Living Things 1. They make use of the organic molecules of life. 2. They consist of one or more cells. 3. They engage in biological processes, such as metabolism and homeostasis. 4. They change throughout their lifetime by growing, mating, and aging. 5. They use DNA as their hereditary material. 6. They have the collective capacity to change over successive generations.