#cell death

Animal Tissue Culture 3

Doxorubicin induces cell death mainly by:

Doxorubicin, anthracycline antibiotic isolated from Streptomyces peucetius subsp. caesius, induces cytotoxicity via dual mechanisms of DNA damage and oxidative stress. Planar tetracyclic chromophore intercalates between DNA base pairs preferentially at CpG sequences increasing helical length and inhibiting topoisomerase IIalpha by trapping covalent enzyme-DNA cleavage complex preventing resealing of transient double-strand breaks introduced during replication, leading to activation of ATM kinase, phosphorylation of histone H2AX at serine139 forming gamma-H2AX foci, p53 accumulation, and mitoch

Ref: Thorn et al PharmGKB Doxorubicin topoisomerase II ROS; Gewirtz DA Biochem Pharmacol 1999 Doxorubicin DNA damage ROS mechanisms.

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Animal Tissue Culture 3

BrdU-labelled cells can be selectively killed by exposure to:

DNA containing BrdU substituted in place of thymidine becomes photosensitive because carbon-bromine bond cleaves homolytically upon absorption of near-UV light around 313 nm or visible light when sensitized by intercalating dyes Hoechst 33258 or acridine orange. Resulting uracilyl radical abstracts hydrogen from deoxyribose causing strand break at apurinic site, creating alkali-labile lesions and single- and double-strand breaks that overwhelm base excision repair leading to cell death if incorporation extensive. This property underlies selective elimination technique: pulse culture with BrdU

Ref: Davidson RL et al PNAS 1974 BrdU photosensitivity light killing; Thermo Fisher BrdU labeling followed by light UV selective cell death.

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Flow cytometry, FACS, ELISA

Which marker is used to detect necrotic cells in FACS?

Necrosis involves rapid pathological loss of membrane integrity without regulated phosphatidylserine exposure or caspase activation. Propidium iodide is a membrane impermeant DNA intercalating fluorescent dye that cannot enter viable or early apoptotic cells with intact membranes. When membrane ruptures in necrosis, dye enters nucleus, binds DNA and emits bright red fluorescence detectable by cytometer. FITC alone is simply a fluorochrome tag, Annexin V marks apoptotic phosphatidylserine exposure, GFP is intrinsic fluorescent protein requiring genetic expression. PI positivity therefore distin

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Apoptosis

Smac/DIABLO promotes apoptosis by

XIAP is a potent inhibitor of caspases-3, -7 and -9. The mitochondrial protein Smac/DIABLO, released during MOMP, binds XIAP and neutralizes its inhibitory activity, thereby facilitating full activation of the caspase cascade. This dual control—release of both cytochrome c and Smac—ensures robust commitment to apoptosis once mitochondria are permeabilized. Careful

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Apoptosis

Which protein directly inhibits caspase-3, -7, and -9?

XIAP, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Apoptosis

Cytochrome c released from mitochondria binds to

Mitochondrial outer-membrane permeabilization (MOMP) releases cytochrome c into the cytosol. Cytochrome c binds Apaf-1, inducing formation of the heptameric apoptosome that recruits and activates caspase-9. Active caspase-9 then propagates the cascade by cleaving executioner caspases. MOMP is therefore the point of no return for the intrinsic apoptotic pathway. Careful

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Apoptosis

The intrinsic apoptotic pathway is triggered primarily by

DNA damage and cellular stress, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Apoptosis

DNA laddering during apoptosis occurs due to cleavage at

Linker DNA between nucleosomes, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Apoptosis

Executioner caspases mainly function to

Initiator caspases (caspase-8, -9 and -10) are activated by dimerization within large multiprotein platforms such as the DISC or the apoptosome. Once active they cleave and thereby activate the executioner caspases (caspase-3, -6 and -7). Executioner caspases proteolytically dismantle structural proteins, activate nucleases and ultimately produce the morphological hallmarks of apoptosis.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Apoptosis

Necroptosis is best described as

Necroptosis is a regulated form of necrotic cell death that occurs when caspase-8 is inhibited or absent. Under these conditions the kinase RIPK1 activates RIPK3, which in turn phosphorylates MLKL. Oligomerized MLKL disrupts plasma-membrane integrity, producing a necrotic morphology. Necroptosis therefore serves as a backup death pathway when apoptosis is blocked, particularly during certain viral infections.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Apoptosis

Why does apoptosis not trigger inflammation?

Apoptosis is an orderly, energy-dependent form of programmed cell death that eliminates cells without provoking inflammation. Characteristic morphological features include cell shrinkage, chromatin condensation (pyknosis), nuclear fragmentation (karyorrhexis), membrane blebbing and formation of apoptotic bodies that display phosphatidylserine as an “eat-me” signal for phagocytes. Rapid clearance of these bodies prevents release of intracellular contents and subsequent inflammation.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Apoptosis

Which feature is NOT associated with apoptosis?

Inflammation, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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