Lysosome
Lysosomes are acidic sacs of enzymes that digest worn-out organelles, engulfed microbes, and large molecules. The pieces are recycled as building blocks, and a single membrane keeps roughly 50 kinds of hydrolase safely walled off from the cytosol.
- 1NucleusOrganelle · double membrane
- 2MitochondrionOrganelle · double membrane
- 3RibosomeMolecular machine · no membrane
- 4Endoplasmic reticulumOrganelle · single membrane network
- 5Golgi apparatusOrganelle · single membrane stacks
- 6LysosomeOrganelle · single membrane
- 7Cell membraneBoundary · phospholipid bilayer
- 8CentriolesMicrotubule pair · organizes the spindle
Animal cell: what you are looking at
A flexible, roughly rounded cell 10–30 µm across, bounded only by its membrane. It has a pair of centrioles near the nucleus and many lysosomes, but no wall, no chloroplasts, and no large central vacuole.
Centrioles. A pair of short microtubule cylinders at right angles; they organize the spindle during cell division.
The lysosome is outlined in coral; it occurs in animal cells, protists, fungi and plants (as lytic vacuoles). Hover or tab through the key to light up the other structures, and click any of them to open its page.
Compare all eight organelles ↗Know its structure
| Found in | Animal cells, Protists, Fungi and plants (as lytic vacuoles) |
| Membranes | One, with a heavily glycosylated inner face that resists the enzymes inside |
| Typical size | About 0.1–1.2 µm across, so it varies from a tiny vesicle to a mitochondrion-sized sac |
| Number per cell | Tens to a few hundred in a typical animal cell; far more in macrophages |
| Contains | Around 50 acid hydrolases (proteases, lipases, nucleases, glycosidases) that work best at pH 4.5–5.0 |
| Discovered | Identified biochemically by Christian de Duve in 1955, work that earned the 1974 Nobel Prize |
What it does
- Digests what the cell takes in. Breaks down proteins, lipids, carbohydrates, and nucleic acids delivered by endocytosis and phagocytosis
- Recycles the cell’s own parts. Autophagy delivers old mitochondria and other organelles for breakdown, returning amino acids and lipids to the cytosol
- Defends. In white blood cells, destroys engulfed bacteria; in osteoclasts, its enzymes are released to dissolve bone
- Senses nutrients. The lysosome surface is where the mTORC1 complex decides whether the cell grows or recycles
Lysosome: common questions
Wondering about the why? Start here.
What does a lysosome do?
A lysosome is a single-membrane sac holding about 50 acid hydrolases that digest proteins, lipids, carbohydrates, and nucleic acids. It breaks down material brought in by endocytosis or phagocytosis, recycles worn-out organelles through autophagy, and in white blood cells destroys engulfed bacteria; the products return to the cytosol as building blocks. Its surface is also where the mTORC1 complex decides whether the cell grows or recycles.
Read: enzymes and activation energyWhy are lysosomes acidic?
A proton pump (V-type ATPase) in the membrane holds the interior at pH 4.5 to 5.0, while the cytosol sits near pH 7.2, a 100- to 500-fold difference in H⁺ concentration. The hydrolases work best at that low pH and are nearly inactive at neutral pH, so if a lysosome leaks its enzymes do little damage. That is why lysosomes are not the “suicide sacs” of old textbooks; programmed cell death is run by caspase enzymes instead.
See the membrane that holds the gradientDo plant cells have lysosomes?
Rarely, and it is one of the classic animal-versus-plant differences. In plants the large central vacuole is acidic and holds hydrolytic enzymes, so it does the digesting; some plant and fungal cells have smaller lytic vacuoles that play the same part. Animal cells hold tens to a few hundred lysosomes, and macrophages that eat bacteria for a living carry far more.
Compare all eight organelles