3.A.2 Cell Division Part I The Cell Cycle and Mitosis In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization.

The cell cycle is a complex set of stages that is highly regulated.

Mitosis is the stage of the cell cycle when the nucleus of the cell divides. Mitosis alternates with interphase in the cell cycle. Interphase is the stage of the cell cyle when the cell is not dividing.

Interphase consists of three phases: G 1 : Gap 1, during which the cell grows and functions normally. S: Synthesis, during which the DNA is replicated. G 2 : Gap 2, during which the cell continues growing and prepares for mitosis. G 1 : Gap 1, during which the cell grows and functions normally. S: Synthesis, during which the DNA is replicated. G 2 : Gap 2, during which the cell continues growing and prepares for mitosis.

The cell cycle is directed by internal controls or checkpoints. Internal and external signals provide stop-and-go signs at the checkpoints.

The G 1 checkpoint decides whether the cell will divide, delay division or enter a resting stage (G 0 ).

The G 2 checkpoint determines if the DNA has been successfully replicated and decides whether the cell is ready to proceed into mitosis.

The M checkpoint occurs during metaphase of mitosis and determines if all chromosomes are correctly aligned on the metaphase plate. This determines whether the cell is ready to proceed with cytokinesis.

Mitosis promoting factor (MPF) is a protein composed of cyclin-dependent kinase (Cdk) and cyclin that promotes the entrance into mitosis.

Only when MPF accumulates past a certain threshold level will the cell proceed from G 2 checkpoint into mitosis.

How MPFs work: Cyclin concentration builds up in the cell throughout interphase. Cyclin binds to CdK and forms the complex MPF. When enough MPF has accumulated, G 2 phase ends and mitosis begins. MPF degrades cyclin, lowering its concentration. After mitosis, cyclin begins accumulating again in the daughter cells. Cyclin concentration builds up in the cell throughout interphase. Cyclin binds to CdK and forms the complex MPF. When enough MPF has accumulated, G 2 phase ends and mitosis begins. MPF degrades cyclin, lowering its concentration. After mitosis, cyclin begins accumulating again in the daughter cells.

Platelet-derived growth factor (PDGF) is one of the numerous proteins that regulate the cell cycle. Problems with PDGF signaling is implicated in a broad range of diseases.

PDGF is a cell signal (ligand) that binds to a PDGF receptor and activates it. The PDGF receptor is a receptor tyrosine kinase.

Cancer results from disruptions in cell cycle control. Because of this, cancer cells reproduce at a rate far faster than normal cells, often forming a mass or tumor.

When a cell specializes, it often enters into a stage where it no longer divides (G 0 ), but it can reenter the cell cycle when given appropriate cues. Nondividing cells may exit the cell cycle or hold at a particular stage in the cell cycle.

Mitosis passes a complete genome from the parent cell to daughter cells. (2n)

Mitosis occurs after DNA replication.

Cytokinesis is the division of the cytoplasm and its contents. Mitosis followed by cytokinesis produces two genetically identical daughter cells. Cytokinesis in animal cells is accomplished by the formation of a contractile ring and a cleavage furrow as the cell is squeezed in the middle by elements of the cytoskeleton.

In plant cells, the rigid cell wall prevents the formation of a cleavage furrow. Instead, vesicles form along a cell plate. The vesicles fuse, forming new cell membrane.

Mitosis plays a role in growth, repair, and asexual reproduction. Aspens can reproduce by cloning.

Mitosis is a continuous process with observable structural features. (replication, alignment, separation). replication alignment separation

Learning Objectives: LO 3.7 The student can make predictions about natural phenomena occurring during the cell cycle. [See SP 6.4] LO 3.8 The student can describe the events that occur in the cell cycle. [See SP 1.2]