IMAT Biology Prep 🔬
Topic: Structure & Function of Cellular Organelles
The busy, microscopic machinery of life.
1. The Eukaryotic Cell: A City of Organelles
Think of a eukaryotic cell as a bustling city. Each organelle is a specialized building or service that performs a vital job to keep the city running.
The Nucleus: City Hall & Library
Contains the cell's genetic material (DNA), which holds the master blueprints for everything the cell does. It's surrounded by a double membrane called the nuclear envelope.
Ribosomes: Construction Workers
Small particles made of rRNA and protein. They read the blueprints (mRNA) from the nucleus and build proteins. Found free in the cytoplasm or attached to the Rough ER.
Endoplasmic Reticulum (ER): The Factory Complex
Rough ER: Studded with ribosomes, it's a protein factory, modifying and folding proteins that will be exported or sent to other organelles.
Smooth ER: Lacks ribosomes. It synthesizes lipids, detoxifies poisons, and stores calcium ions.
Golgi Apparatus: Post Office & Shipping Center
Receives proteins and lipids from the ER, further modifies, sorts, and packages them into vesicles for delivery to their final destination.
Lysosomes: Recycling & Waste Disposal Plant
Vesicles filled with digestive (hydrolytic) enzymes. They break down old organelles, food particles, and ingested viruses or bacteria.
Mitochondria: The Power Plants
The site of cellular respiration. They convert chemical energy from food (like glucose) into ATP, the main energy currency of the cell. They have their own DNA and ribosomes.
2. Visualizing an Animal Cell
3. 🧠 Medical Case Study: Lysosomal Storage Disease
An infant is brought to a pediatrician showing developmental regression, muscle weakness, and an exaggerated startle response to noise. A physical exam reveals a "cherry-red spot" on the retina of the eye. Genetic testing confirms a diagnosis of Tay-Sachs disease.
Question: Based on the function of organelles, which organelle is malfunctioning in Tay-Sachs disease?
Answer & Explanation:
The malfunctioning organelle is the lysosome.
- The Problem: Tay-Sachs is a lysosomal storage disease. It is caused by a genetic mutation in the gene for an enzyme called hexosaminidase A. This enzyme is crucial for breaking down a fatty substance (lipid) called GM2 ganglioside.
- Organelle Function: The lysosome is the cell's recycling center. When the hexosaminidase A enzyme is absent or deficient, the lysosome cannot break down GM2 ganglioside.
- Consequence: The lipid accumulates to toxic levels, particularly in the nerve cells of the brain and spinal cord, leading to their progressive destruction. This causes the severe neurological symptoms seen in patients.
- Takeaway: This case tragically illustrates how a defect in a single enzyme within a single organelle can have devastating consequences for the entire organism. It highlights the critical importance of proper organelle function.
4. 📊 Concept Check: True or False?
5. 📝 IMAT-Style Practice Questions
6. 🧾 Key Takeaways Summary
- Nucleus: Contains and protects DNA; controls cell activities.
- Ribosomes: Synthesize proteins.
- Rough ER: Folds and modifies proteins for export.
- Smooth ER: Synthesizes lipids and handles detoxification.
- Golgi Apparatus: Sorts, packages, and ships cellular products.
- Lysosomes: Digest waste, old organelles, and pathogens.
- Mitochondria: Generate ATP through cellular respiration.
- Compartmentalization: The division of labor among organelles allows eukaryotic cells to function efficiently and with high complexity.