Summary
Programmed cell death carried out by caspase enzymes, removing damaged or unneeded cells without inflammation.
In depth
Apoptosis can be triggered by internal signals (intrinsic pathway via mitochondria, cytochrome c and the apoptosome) or external death ligands (extrinsic pathway, such as Fas). Initiator caspases activate executioner caspases, which cleave cellular proteins. The cell shrinks, blebs and is engulfed by phagocytes.
Unlike necrosis, which is accidental and causes inflammation, apoptosis is tidy and controlled. Bcl-2 family proteins decide whether a cell commits.
Apoptosis shapes the body during development: it removes the webbing between fingers and toes, eliminates self-reactive immune cells and sculpts the nervous system, where about half of neurons made die. The nematode C. elegans lets researchers follow it exactly, since 131 of its 1090 cells die in a fixed pattern, which led to the identification of the ced genes and a 2002 Nobel Prize.
Bcl-2 family proteins decide the intrinsic path: Bax and Bak make pores in mitochondria and release cytochrome c, while Bcl-2 prevents this. Too little apoptosis contributes to cancer and autoimmune disease, too much to neurodegeneration.
Remember: apoptotic cells are packaged and removed without inflammation, while necrotic cells burst and release signals that alert the immune system.
Frequently asked questions
What is Apoptosis?
Programmed cell death carried out by caspase enzymes, removing damaged or unneeded cells without inflammation.
Which area of biology covers Apoptosis, and how advanced is it?
Apoptosis is one of the 52 topics in Cell Biology. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Autophagy, Cyclin-Dependent Kinases, Facilitated Diffusion.
Can you give an example of Apoptosis?
The webbing between embryonic fingers disappears through apoptosis.
What should I learn before Apoptosis?
Work through the Beginner topics in Cell Biology first, such as Cell Theory, Prokaryotic Cell, Eukaryotic Cell, then return to Apoptosis. Advanced topics assume the Intermediate vocabulary.
What topics are related to Apoptosis?
The closest topics to Apoptosis are Autophagy, Cyclin-Dependent Kinases, Facilitated Diffusion, Cell Differentiation. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Apoptosis?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Apoptosis. To practise the whole of Cell Biology, use the Cell Biology quiz.
How is Apoptosis different from Autophagy?
Apoptosis: Programmed cell death carried out by caspase enzymes, removing damaged or unneeded cells without inflammation. Autophagy: A recycling pathway in which cytoplasmic components are enclosed in autophagosomes and degraded by lysosomes. Read both side by side and note what each one explains.
How should I study Apoptosis step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Autophagy and explain the difference aloud. Finally, take the Cell Biology quiz and come back to this page for any question you miss.