Chap 12 The Cell Cycle

Kangaroo rat epithelial cells

Phases of the Cell Cycle G1 – gap phase 1 Primary growth phase Longest phase for most cells S – Synthesis DNA replicate is made via transcription

G2 – gap phase 2 Second growth phase Preparation for separation of replicated genome Mitochondria and other organelles replicate now Microtubules assemble at a spindle

M – Mitosis Cell nucleus proceeds through PMAT Cytokinesis – cytoplasmic division Cell plate forms in plant cells microfilaments constrict around middle of cell resulting in cell cleavage.

Cell Cycle Regulation The timing and rate of division in cells is crucial to normal growth and development. The frequency of division varies with the type of cell

Cell Cycle Control System This control system both triggers and coordinates key events in the cell cycle. This system proceeds on its own, driven by a built-in clock, yet regulated at certain checkpoints by both internal and external controls. Checkpoint – critical point where “stop and go” signals are relayed.

Three major checkpoints are found: G1 checkpoint - primary point where external signals can alter events. Linked to growth and prep for DNA synthesis. G2 checkpoint – linked to growth and prep for division. M checkpoint - assures that all chromosomes are attached to spindle fibers prior to anaphase.

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