Importance of Cell Growth Control
Cells are continuously lost and replaced.
Uncontrolled growth can result in tumors, necessitating regulated timing and location of division.
Factors Influencing Cell Division
Growth Factors: Proteins that promote cell replication, crucial for processes like wound healing.
Contact Inhibition: Cells stop dividing upon touching others.
Anchorage Dependence: Cells require anchoring to extracellular matrix for growth signals.
Cell Cycle Checkpoints: Points for assessing conditions before cell division.
G1 Checkpoint: Checks nutrients, growth signals, DNA damage; allows repair or triggers apoptosis.
G2 Checkpoint: Verifies cell size and DNA replication completion before mitosis.
Cell Cycle Phases: Cells can enter a resting phase (G0). Neurons may stay in G0 for life, while liver cells can re-enter the cycle if damaged.
Internal Regulation of Cell Cycle
Proto-Oncogenes: Promote cell cycle progression; mutations can convert them into oncogenes, causing uncontrolled growth.
Tumor Suppressor Genes: Inhibit cell growth; mutations lead to a failure in growth control.
Tumor Formation: Results from gene mutations causing unregulated cell growth due to space issues or timing errors.
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