organelles
Summary
Organelles are specialized compartments inside a cell, each with a specific job. Most eukaryotic organelles are membrane-bound, which lets incompatible reactions run in separate conditions. Most testable: match each organelle to its function and follow the protein path from rough ER to Golgi to the cell surface.
Detail
Meaning: Organelles are specialized compartments or structures inside a cell, each carrying out a specific job. In eukaryotes most are enclosed by membranes, so reactions that need different conditions can run side by side. Examples: nucleus (DNA storage, transcription), rough ER (ribosomes make secreted and membrane proteins), smooth ER (lipid synthesis, detoxification, Ca²⁺ storage), Golgi apparatus (modifies, sorts, and packages proteins), lysosomes (acid hydrolases digest material), peroxisomes (fatty acid breakdown, H₂O₂ handling), and mitochondria (Krebs cycle and oxidative phosphorylation).
On the MCAT: A passage describes a defect, mutation, or treatment and asks which organelle is affected or which process would fail. Know the protein path: ribosome on rough ER → vesicle → Golgi → vesicle → plasma membrane or secretion. Mitochondria have a double membrane, their own circular DNA, and their own ribosomes, which supports the endosymbiotic theory.
Common confusion: Ribosomes are not membrane-bound, and prokaryotes have them even though prokaryotes have no membrane-bound organelles. Glycolysis happens in the cytosol, not the mitochondrion. Lysosomes digest with hydrolases at low pH, while peroxisomes handle peroxides and fatty acids.
Sources
- Campbell Biology
- Molecular Biology of the Cell
- Biology (Raven)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.