G2 checkpoint

Examples of G2 checkpoint in the following topics:

• Regulation of the Cell Cycle at Internal Checkpoints

  • These checkpoints occur near the end of G1, at the G2/M transition, and during metaphase .
  • The G2 checkpoint bars entry into the mitotic phase if certain conditions are not met.
  • However, the most important role of the G2 checkpoint is to ensure that all of the chromosomes have been accurately replicated without mistakes or damage.
  • The cell cycle is controlled at three checkpoints.
  • Proper chromosome duplication is assessed at the G2 checkpoint.

• Interphase

  • The three stages of interphase are called G1, S, and G2 .
  • In the G2 phase, the cell replenishes its energy stores and synthesizes proteins necessary for chromosome manipulation.
  • There may be additional cell growth during G2.

• Regulator Molecules of the Cell Cycle

  • In addition to the internally controlled checkpoints, there are two groups of intracellular molecules that regulate the cell cycle.
  • Two groups of proteins, called cyclins and cyclin-dependent kinases (Cdks), are responsible for the progress of the cell through the various checkpoints.
  • The different cyclins and Cdks bind at specific points in the cell cycle and thus regulate different checkpoints.
  • For the cell to move past each of the checkpoints, all positive regulators must be "turned on" and all negative regulators must be "turned off."
  • There is a direct correlation between cyclin accumulation and the three major cell cycle checkpoints.

• Proto-oncogenes

  • For example, a mutation that allows the Cdk gene to be activated without being partnered with cyclin could push the cell cycle past a checkpoint before all of the required conditions are met.
  • In addition to the cell cycle regulatory proteins, any protein that influences the cycle can be altered in such a way as to override cell cycle checkpoints.

• Tumor Suppressor Genes

  • This discovery is not surprising in light of the multiple roles that the p53 protein plays at the G1 checkpoint.
  • Essentially, without a fully functional p53, the G1 checkpoint is severely compromised and the cell proceeds directly from G1 to S regardless of internal and external conditions.

• Cell Signaling and Cell Death

  • There are many internal checkpoints that monitor a cell's health; if abnormalities are observed, a cell can spontaneously initiate the process of apoptosis.

• Meiosis I

  • Finally, during the G2 phase (also called the second gap phase), the cell undergoes the final preparations for meiosis.

• The Evolution of Roots in Seedless Plants

  • The endodermis is exclusive to roots, serving as a checkpoint for materials entering the root's vascular system.

• Programmed Cell Death

  • There are many internal checkpoints that monitor a cell's health; if abnormalities are observed, a cell can spontaneously initiate the process of apoptosis.