What are Cell Organelles? Functions, Structure & Complete List
Organelles are specialized, membrane-bound or non-membrane structures within eukaryotic cells that act as cellular 'organs' to perform vital biochemical operations: ATP energy generation, protein synthesis, intracellular digestion, waste recycling, and lipid metabolism.
Cell Organelles Quick Classification
1. Non-Membranous Organelles
A. Ribosomes (Protein Synthesizers)
Composed of rRNA (60%) and proteins (40%), ribosomes translate messenger RNA (mRNA) into polypeptide chains. Found in all living cells.
B. Centrosome (Microtubule Organizing Center)
Consists of two centrioles aligned perpendicularly. Forms the mitotic spindle during cell division in animal cells.
2. Single-Membrane Organelles
- Endoplasmic Reticulum (ER): Rough ER (studded with ribosomes, synthesizes secretory proteins) and Smooth ER (lipid synthesis, detoxification, and Ca²⁺ storage).
- Golgi Apparatus: Modifies, sorts, and packages macromolecules into vesicles.
- Lysosomes: Filled with acid hydrolases (pH ~4.5-5.0) for autophagy, intracellular digestion, and programmed apoptosis.
- Peroxisomes: Perform fatty acid beta-oxidation and neutralize toxic hydrogen peroxide (H₂O₂) via catalase.
- Vacuoles: Storage compartments; central vacuole in mature plant cells maintains turgor pressure.
3. Double-Membrane Organelles
A. Mitochondria (The Powerhouse of the Cell)
Site of cellular respiration and ATP synthesis via oxidative phosphorylation. Features an inner folded membrane (Cristae) and a fluid Matrix containing circular mtDNA and 70S ribosomes (Endosymbiotic Theory).
B. Chloroplasts and Plastids
Found exclusively in plants and algae. Chloroplasts harness solar energy via Thylakoid/Grana membranes and Stroma to synthesize glucose through photosynthesis.