考研资料：北京大学细胞生物学第十一章+细胞增殖极其调控下

3. Cytokinesis(1) In animal cells The MT of mitotic spindle determine the plane of animal cell division; Mitosis can occur without cytokinesis. vContractile ring: Actin and myosinII in the contractile ring generate the force for cytokinesis(2) In plant cells: The phragmoplast guides cytokinesis in higher plants; The assembly of the cell plate begins in late anaphase and is guided by phragmoplast4. MeiosisvThe comparison of meiosis and mitosisvTwo major contributions to the reassortment of genetic material that occurs in the production of gametes during meiosis.Visible evidence of crossing overvComparison of the mechanisms of chromosome alignment (at metaphase) and separation (at anaphase) in meiotic division I and meiotic division II.vMeiotic chromosome pairing culminates in the formation of the synaptonemal complexvInfluence of Sry on gonad development.The stages of oogenesis and spermatogenesis 5. The cell-cycle control systemA. The cell-cycle control system triggers the major processes of the cell cycleB. The control system can arrest the cell cycle at specific checkpointsC. The cell cycle control system is based on cyclically actived protein kinases-cyclin-dependent kinases (Cdks). Engine molecules for cell cycle G1checkpoint: fission yeast cells: Start point；Animal cells: Restriction PointD. MPF (Maturation-promoting factor，Mitosis-promoting factor)Lab. of Toronto Univ and Yale Univ.maturation promoting factor,MPFPurdue Univ.:Behavior of MPFThe fusion of M-phase HeLa cell with Ptk cell (G1、 S、 G2) inducing PCC. Exp. Demonstration that cells contain factors that stimulate entry into mitosis.；vThe prematurely condensed chromosome (PCC)MPF(M-Cdk):p34cdc2cyclinBTwo subunits:Catalytic subunit transfers P from ATP to Ser and Thr;Regulatory subunit called cyclin(Marine Biological Lab.at Woods Hole and UC BerkeleyUniv. of Oxford-yeast)E. A simplified view of the core of the cell-cycle conreol systemCdk associates successively with different cyclins to trigger the different events of the cycle.Cdk activity is usually terminated by cyclin degradation.Tree of cyclins are required in all eucaryotic cells:1. G1/S-cyclins bind Cdks at the end of G1 and commit the cell to DNA replication.2. S-cyclins bind Cdks during S phase and are required for the initiation of DNA replication.3. M-cyclins promote the events of mitosis.vThe structural basis of Cdk activationThe human Cdk2 is shown in three states: (A) In the inactive, without cyclin bound, the active site is blocked by a region of the protein called the T-loop; (B) The binding of cyclin causes the T-loop to move out of the active site, resulting in partial activition of Cdk2; (C) Phosphorylation of Cdk2 by CAK at a threonine residue in the T-loop, fully active.vCdk activity can be suppressed both by inhibitory phosphorylation (pp586:14.6) and by inhibitory proteins (CKIs).P27 Cdk inhibitor proteins(CKIs)vThe cell-cycle control system depends on cyclical proteolysis-The control of proteolysis by SCF and APC during the cell cycle. (A)The phosphorylation of a target protein(CKI),allows the CKI to be recognized by SCF (constitutive active), E1and E2(two additional proteins), SCF serves as a ubiquitin ligase.The ubiquitylated CKI is then immediately recognized and degraded in a proteasome.SCF mediate the destruction of G1-cyclins, Cdk inhibitor,and other cell cycle proteins.(B)M-cyclin ubiquitylation is performed by APC.In G1 and S phaseIn metaphase/anaphase M-cyclinsF. Intracellular control of cell-cycle eventsvS-phase Cyclin-Cdk complexes (S-Cdks) initiate DNA replication once per cycleEvidence from cell-fusion exp. For a replication block. vThe initiation of DNA replication once per cell cycle.ORC: origin recognition complex;Cdc6: regulatory protein, it is present at low levels during most of the cell cycle but increases transiently in early G1,where it is required for the binding of a complex composed of a group of closely related proteins,the Mcm proteins.vThe activation of M-phase cyclin-Cdk complexes (M-Cdks) triggers entry into mitosisThe activation of M-CdkvThe DNA replication checkpoint: Entry into mitosis is blocked by incomplete DNA replicationThe experiments of DNA replication checkpoint in the mammalian cells in culture were treated with caffeine and hydroxyurea.vThe spindle-attachment checkpoint: Unattached chromosomes block sister-chromatid separation v The sister chromatid separation is triggered by proteolysisThe triggering of sister-chromatid separation by the APC.APC: anaphase-promoting complexThe destruction of Securin allows separase to cleave the cohesin complex.Securin(后期抑制因子 )separasecohesin1. Mad2 is normally localized at the kinetochores of prometaphase and misaligned metaphase chromosomes. Mad2 provides a “wait” signal that delays a cells progression into anaphase. The cell that possess mutant Mad2 fail to arrest at metaphase when their chromosomes are misaligned.Mad2 bind to Cdc20, inhibiting its activation of the APC, an event that is required for the metaphase-to-anaphase transition.It is only after the Mad2 is absent from all of the chromosomes that APC activation can occur and anaphase can begin.2. The cell that contains Monoattached chromosome delays the onset of anaphase until the chromosome becomes a biattached chromosome and aligned at the equator.vMad2 prot