BSCI 330 Lecture Notes - Lecture 11: Mitogen, Sister Chromatids, Cell Membrane
Document Summary
Yeast are commonly used model systems for cell division. Fission yeast (s. pombe: divide by medial fission. Gia(cid:374)t: gro(cid:449) a lot, (cid:271)ut do(cid:374)"t di(cid:448)ide: cdk mutation to prevent formation of m-cdk complex, cdc25 inactivation mutation, wee1 hyperactive or upregulated. Then how could it proceed past the checkpoint to get to mitosis and divide: possible that cdk is (constitutively) constantly active, so the cell is constantly dividing. Structural change in cdk to make site constantly active regardless of phosphorylation: hyperactive cdc25. Wee1 localizes in the opposite direction from cdc25. Cdk-1 and m-cyclin associate to form inactive m-cdk. Cak and wee 1 add phosphates to cdk-1 (activating and inhibitory) Phosphorylated cdc25 removes inhibitory phosphate from cdk-1: yields active m-cdk. Positive feedback from active m-cdk to wee1. M-cyclin degraded at metaphase-anaphase transition -> key. Xenopus extracts: remove cytoplasm from unfertilized xenopus eggs (mitotic extract, add nucleus from sperm (contains centrosome, spindles spontaneously form, add calcium to cause cells to complete mitosis.