Paper I
Question
Morphological changes in apoptosis.
Answer
Light microscopic changes
- Cell shrinkage — the cell becomes smaller, with condensed cytoplasm and densely packed organelles
- Chromatin condensation — the most characteristic feature, with chromatin aggregating peripherally under the nuclear membrane into dense masses
- Formation of cytoplasmic blebs
- Nuclear fragmentation — the nucleus breaks into multiple discrete fragments (karyorrhexis)
- Formation of apoptotic bodies — the cell fragments into membrane-bound bodies containing cytoplasm and organelles (with or without nuclear fragments), which are then phagocytosed by neighbouring cells/macrophages
Key distinguishing features from necrosis
- Plasma membrane remains intact throughout the process (until phagocytosis) — no leakage of cellular contents
- No accompanying inflammatory response (unlike necrosis)
- Affects single cells or small clusters, not confluent tissue
Biochemical hallmark
- Internucleosomal DNA cleavage by endonucleases, producing DNA fragments in multiples of ~180-200 base pairs, giving a characteristic “laddering” pattern on gel electrophoresis