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• The cell cycle consists of several phases:

  • M phase: mitosis (karyokinesis & cytokinesis)

  • G1 phase: growth

  • S phase: DNA replication

  • G2 phase: growth

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• M phase lasts for 30-43 minutes and includes mitosis (nuclear division) and cytokinesis.

• G2 phase is the cytoplasmic division.

• G2 interphase occurs before mitosis.

• S phase is the DNA replication phase.

• G1 phase is the longest phase and is a growth phase.

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• Mitotic spindle assembly and complete cell division are triggered by the machinery and completion of mitosis.

• Checkpoints, such as the M checkpoint, G2 checkpoint, and G1 checkpoint, determine if the cell is ready for the next phase.

• The S checkpoint triggers DNA replication machinery to replicate DNA.

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• Checkpoints, such as the G2 checkpoint, M checkpoint, and G1 checkpoint, ensure that the DNA is intact and the environment is favorable for cell division.

• If something goes wrong in the cell, it will stop at a checkpoint and fix the DNA.

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• Cyclin-dependent kinase (Cdk) and cyclin control the cell cycle.

• Cyclin-dependent kinase (Cdk) is also known as maturation promoting factor (MPF).

• Cyclin causes the activation of cyclin-dependent kinase (Cdk).

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• The cyclin/Cdk complex is necessary for cell division during mitosis and interphase.

• M-Cdk activity and M-cyclin concentration play a role in the cell cycle.

• Ubiquitination marks cyclin for destruction.

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• Proteosomes degrade proteins that are ubiquitinated, including cyclin.

• The cell recycles M-cyclin and undergoes the destruction of M-cyclin and inactivation of M-Cdk.

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• Xenopus oocyte is used to study the cell cycle.

• MPF was first discovered in oocytes of Rana (leopard frog) by Dr. Yoshio Masui in 1971

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• Phosphorylation modulates MPF.

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• Autophosphorylation produces an abrupt increase in active MPF.

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• Table showing the major cyclins and Cdks of vertebrates.

• Different cyclin-Cdk complexes are involved in different phases of the cell cycle.

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• Cyclin B is involved in the entry into mitosis.

• Phosphorylation cascade results in chromatin condensation, disassembly of the nuclear envelope, and reorganization of microtubules.

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• Cyclin A is involved in the entry into S-phase.

• Cyclin A plus Cdk2 begins S-phase.

• Cdc6 is pre-assembled onto the origin and is removed and destroyed by cyclinA/Cdk2 to prevent rereplication of DNA.

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• Origin of replication is controlled by S-Cdk.

• S-checkpoint ensures proper DNA replication.

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• G1 checkpoint and S checkpoint play a role in the cell cycle.

• Mutations in the p53 gene are implicated in various cancers.

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• G1 checkpoint involves ubiquitin ligase (Mdm2).

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• Apoptosis is regulated by the Bcl-2 protein family.

• Some Bcl-2 proteins are apoptosis activators, while others are inhibitors of apoptosis.

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• The cell cycle consists of four phases: G1, S, G2, and M.

• G1 phase prepares the cell for DNA replication.

• G2 phase prepares the cell for mitosis and cytokinesis.

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• M-Cdk phosphorylates condensin proteins.