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#sister chromatids

5 public questions tagged with this topic.

Cell Division

Which enzyme is responsible for breaking down cohesin to allow sister chromatid separation?

Sister chromatid cohesion mediated by cohesin ring complex with SMC1 and SMC3 coiled-coil proteins forming V-shaped dimer bridged by kleisin Rad21 that closes tripartite ring embracing both sister DNAs from replication until anaphase. Opening requires proteolytic cleavage rather than dissociation. Separase, large 230 kDa cysteine endopeptidase belonging to CD clan with catalytic histidine-cysteine dyad analogous to caspases, serves as cleaving enzyme. Before anaphase, separase kept inactive through two layers: binding of securin pseudosubstrate occupying active site, and cyclin B-CDK1 mediated

Ref: Uhlmann et al., Nature 2000, Mechanism of Separase. Nasmyth, Science 2002, Cohesin Cleavage.

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Cell Division

The separation of sister chromatids occurs during:

Separation of sister chromatids underlies chromosome segregation during anaphase and relies on coordinated dissolution of cohesin and activation of motor mechanisms. Throughout S phase and G2, cohesin ring comprising Smc1, Smc3, and kleisin Rad21 embraces sister DNAs, establishing cohesion resisting spindle pulling until timely release. Shugoshin-PP2A protects centromeric cohesion specifically until anaphase onset. Upon satisfaction of spindle assembly checkpoint, APC/C-Cdc20 ubiquitinates securin and cyclin B with K11 chains for proteasomal destruction. Securin degradation frees separase endo

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 17, Anaphase Mechanisms. Nasmyth, Annu Rev Genet 2009.

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Basics of Inheritance

Segregation of sister chromatids occurs during

Segregation of sister chromatids occurs during anaphase II of meiosis when centromeric cohesin is cleaved by separase, sister kinetochores pulled toward opposite poles. At this stage cells are already haploid after meiosis I, so division resembles mitotic separation, maintaining ploidy while distributing recombinant chromosomes carrying crossover products. Chromatids bearing different alleles after exchange go to distinct gametes. Anaphase I separates homologs, metaphase I aligns bivalents, prophase II prepares spindle without segregation, timing critical for haploid gamete fidelity. Cytologic

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 3: Meiosis II

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