Regulation of Cell Cycle

Regulation of Cell Cycle

Regulation of the Cell Cycle Overview

  • The cell cycle comprises specific stages including interphase (growth), mitosis (nuclear division), and cytokinesis (cell division).
  • The progression through these stages is governed by cell cycle control systems and is crucial for the healthy growth and division of cells.
  • Faulty regulation can lead to diseases like cancer, where cells proliferate out of control.

Cell Cycle Checkpoints

  • Checkpoints are control mechanisms in eukaryotic cells which ensure correct cell cycle progression.
  • There are key checkpoints in the cell cycle: G1 checkpoint, G2 checkpoint, and M checkpoint. Each checks for certain conditions before permitting the cell to progress to the next stage of the cell cycle.

G1 Checkpoint

  • The G1 checkpoint, also known as the restriction point, is a point at which the cell irreversibly commits to cell division.
  • Checks for sufficient energy resources, nutrients, correct DNA, and other factors needed for DNA synthesis and cell division.

G2 Checkpoint

  • The G2 checkpoint bars entry into the mitotic phase if certain conditions are not met.
  • Checks for DNA damage and ensures all of the DNA has been replicated.

M Checkpoint

  • The M checkpoint ensures that all sister chromatids are correctly attached to the spindle microtubules before anaphase proceeds.
  • This checkpoint prevents the separation of duplicated chromosomes until each chromosome is properly attached to the spindle apparatus.

Proteins in Cell Cycle Regulation

  • Several proteins are crucial for the regulation of the cell cycle, including cyclins and cyclin-dependent kinases (CDKs).
  • The levels of cyclins increase and decrease during the cell cycle, which controls the activity of CDKs.
  • Active CDKs trigger different events in the cell cycle by phosphorylating target proteins.

Role of External Signals

  • External signals can also regulate cell cycle progression.
  • Growth factors can stimulate cells to move from G0 to G1 and from G1 to S phase.
  • Withholding growth factors can arrest cell cycle progression.
  • Contact inhibition, a process that halts cell division when cells come into contact with each other, also plays a role in preventing uncontrolled cell proliferation.

Cancer and the Cell Cycle

  • Cancer is often the result of uncontrolled cell division, which can occur due to mutations in genes responsible for regulating the cell cycle.
  • These mutated genes can lead to unchecked cell division by disrupting normal cell cycle control mechanisms, leading to the formation of tumours.