Nucleus, endoplasmic reticulum, Golgi, mitochondria, lysosomes and peroxisomes
Mnemonic
Match each organelle to its job and to a disease of its failure:
- Nucleus - DNA, transcription
- Rough endoplasmic reticulum - protein synthesis for export. Abundant in plasma cells and pancreatic acinar cells
- Smooth endoplasmic reticulum - lipid and steroid synthesis, detoxification. Abundant in liver and adrenal cortex
- Golgi apparatus - modification, sorting and packaging, adding mannose-6-phosphate to target enzymes to lysosomes
- Lysosomes - acid hydrolases. Failure causes the lysosomal storage disorders
- Peroxisomes - very long chain fatty acid oxidation. Failure causes adrenoleukodystrophy and Zellweger syndrome
- Mitochondria - oxidative phosphorylation, maternally inherited DNA
- Proteasome - degrades ubiquitinated proteins
“Rough makes protein, smooth makes lipid, Golgi ships it, lysosome destroys it.”
I-cell disease illustrates the Golgi’s role precisely: failure to add mannose-6-phosphate means lysosomal enzymes are secreted instead of delivered, so they are found in high concentration in the plasma and absent from the lysosome.
Expansion
| Organelle | Function | Prominent in |
|---|---|---|
| Nucleus and nucleolus | DNA, ribosome assembly | All nucleated cells |
| Rough endoplasmic reticulum | Protein synthesis for export | Plasma cells, pancreatic acinar cells |
| Smooth endoplasmic reticulum | Lipid and steroid synthesis, detoxification, calcium store | Hepatocytes, adrenal cortex, Leydig cells |
| Golgi apparatus | Modification, packaging and sorting | Secretory cells |
| Mitochondria | ATP by oxidative phosphorylation | Cardiac muscle, renal tubule, brown fat |
| Lysosomes | Acid hydrolase digestion | Macrophages, neutrophils |
| Peroxisomes | Very long chain fatty acid oxidation, catalase | Liver, kidney |
| Proteasome | Ubiquitinated protein degradation | All cells |
The appearance under the microscope follows the function: a cell packed with rough endoplasmic reticulum stains basophilic because of the ribosomal RNA, which is why plasma cells have deep blue cytoplasm; a steroid-secreting cell is full of smooth endoplasmic reticulum and lipid droplets, so it looks pale and vacuolated.
Diseases map onto organelles: lysosomal storage disorders, peroxisomal disorders such as Zellweger syndrome and adrenoleukodystrophy, and mitochondrial disease with its maternal inheritance and heteroplasmy.