Mitosis Promoting Factor (MPF) Note sheet

-Mitosis-promoting factor (MPF) is present in the cytoplasm of M-phase cells and induces mitosis. It is composed of two distinct subunits:

  • Cyclin
  • Kinase

The protein kinase is an enzyme that catalyzes the transfer of a phosphate group from ATP to a target protein (phosphorylation).

The cyclin subunit functions as a regulatory protein.

-Cyclin concentration regulates MPF concentration

The concentration of MPF cyclin increases during interphase and peaks in M phase before decreasing again.

The MPF protein kinase is a cyclin-dependent kinase (Cdk), so it is only active when bound to the cyclin subunit.

When cyclin concentrations are high, more MPF is active. The target proteins are phosphorylated, initiating mitosis.

-MPF Activation

After it binds to cyclin, MPF’s Cdk subunit becomes phosphorylated at two sites. This event renders the Cdk subunit inactive.

Late in the G2 phase, enzymes cause one of the phosphate groups on the Cdk subunit to drop off.

This dephosphorylation reaction changes MPF’s shape by activating it.

-MPF Deactivation

During anaphase, an enzyme complex begins degrading MPF’s cyclin subunit. MPF triggers a chain of events that leads to its own destruction.

Process: the G1 checkpoint is subject to social control

Easier explanation:

Growth factor – E2F

If E2F is bound to Rb, will not enter S phase

Phosphate group is added, E2F is released, growth factor is floating around cell and pushes into S phase

When Rb is overwhelmed and can’t bind E2F, E2F will be floating around cell and push cell into S phase over and over

Or overproduction ofcylin

Both cause cancer

Check for understanding – could you answer these questions?

  1. What are the components of MPF and how do they differ?

Mitosis Promoting Factor…2 components are cylin and kinase.

Cylin is regulating when the cell division occurs (telling kinase what to do) and kinase actually carrying out phosphorylation (which means the addition of a phosphate group)

  1. When is concentration of the Cyclin component of MPF the highest and what triggers MPF’s activation for mitosis?

Two phosphates will join, then one is removed, and that’s what activates the MPF and then the cell begins Mitosis

  1. When does MPF degrade?

Happens in Anaphase

The enzymes are targeting the cyclin

Kinase stays same concentration throughout cell cycle