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Chapter 21 Regulation of the Eukaryotic Cell Cycle. April 6, 2005 Presented by: Jennifer Payne. 21.1 Overview of the Cell Cycle and Its Control 21.2 Biochemical Studies with Oocytes, Eggs, and Early Embryos 21.3 Genetic Studies with S. pombe
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Chapter 21Regulation of the Eukaryotic Cell Cycle April 6, 2005 Presented by: Jennifer Payne
21.1 Overview of the Cell Cycle and Its Control 21.2 Biochemical Studies with Oocytes, Eggs, and Early Embryos 21.3 Genetic Studies with S. pombe 21.4 Molecular Mechanisms for Regulating Mitotic Events 21.5 Genetic Studies with S. cerevisiae 21.6 Cell-Cycle Control in Mammalian Cells 21.7 Checkpoints in Cell-Cycle Regulation Sections within the Chapter
21.1 Overview of the Cell Cycle and Its Control • There are ordered series of events that eukaryotic cells proceed through, which constitutes the cell cycle. • During the cell cycle the cells chromosomes are duplicated and one copy of each of the chromosomes segregates into two daughter cells. • The regulation of the cell cycle is essential for normal cell development of multicellular organisms. Any loss of control can result in cancer, a disease that leads to death in one in every six people.
Overview continued • Cell replication is primarily controlled by regulating the timing of two critical events in the cell cycle: nuclear DNA replication and mitosis. • The main controllers of these events are heterodimeric protein kinases that contain a regulatory subunit and a catalytic subunit. • The kinases regulate the activities of multiple proteins involved in DNA replication and mitosis by phosphorylating them at specific regulatory sites, activating some and inhibiting others to coordinate their activities.
The Ordered Series of Events Leading to Replication of Cells • The cell cycle is divided into four major phases: 1. S phase 2. G2 phase 3. M phase 4. G1 phase • Each of these phases have their own series of events until the cell is duplicated into two daughter cells at the end of the M phase. • The M phase is when the process of mitosis occurs.
Four Phases of the Cell Cycle • In the S (synthesis phase) the chromosomes are replicated. • After the cell progresses through the G2 phase the cell then begins mitosis. • Mitosis occurs during the M phase of the cell cycle. Mitosis is divided into several different stages.
Following Mitosis • The G1 phase follows mitosis. This phase is the period before DNA synthesis is reinitiated into the S phase. • In vertebrates and diploid yeasts the cells in G1 have a diploid number of chromosomes (2n), one inherited from each parent. • In haploid yeasts, cells in G1 have one of each chromosome (1n).
Length of the Cell Cycle • There are rapidly replicating human cells that progress through the entire cell cycle in approximately 24 hours. • Mitosis takes around 30 minutes; G1, 9 hours; S phase, 10 hours; and G2, 4.5 hours. • In growing yeast cells the cycle only takes about 90 minutes combined.
Postmitotic Cells • The postmitotic cells can leave the cell cycle and remain for days, weeks, or sometimes the lifetime of the organism. • Cells that remain the lifetime of the organism does not proliferate any further. • In vertebrates cells leave the cell cycle in G1 phase and enter into a phase called G0. • G0 cells returning to the cell cycle enter into the S phase.
