Chromosomes
Immediately after DNA replication a human cell will have 46 “double chromosomes”. In each double chromosome there are two copies of that chromosome’s DNA molecule. During mitosis the double chromosomes are split to produce 92 “single chromosomes”, half of which go into each daughter cell. During meiosis, there are two chromosome separation steps which assure […]

The cell cycle or cell-division cycle (CDC) is the series of events in a eukaryotic cell between one cell division and the next. Thus, it is the process by which a single-cell fertilized egg develops into a mature organism and the process by which hair, skin, blood cells, and some internal organs are renewed. A […]

The Cell Cycle
Interphase
Metaphase
Mitosis
The cell cycle of a typical eukaryotic cell has four phases. The relatively brief M phase consists of nuclear division (mitosis) and cytoplasmic division (cytokinesis). After M phase, the daughter cells each begin interphase of a new cycle. Although the various stages of interphase are not usually morphologically distinguishable, each phase of the […]

Cyclins and cyclin-dependent kinases (CDKs) are the two critical classes of molecules in regulation of cell cycle progression. Cyclins form the regulatory subunits and CDKs the catalytic subunits of an activated heterodimer; cyclins have no catalytic activity and CDKs are inactive in the absence of a partner cyclin. When activated by a bound cyclin, CDKs […]

Checkpoints
Checkpoints are used by the cell to monitor and regulate the progress of the cell cycle. If a cell fails to meet the requirements of a phase it will not be allowed to proceed to the next phase until the requirements have been met. Several checkpoints are designed to ensure that damaged or incomplete DNA […]