Cell tissue classification in terms of ability to regenerate

1. Labile cells: - Bone marrow, testis, small, bowel (all contain stem cells)
2. Stable cells: liver, kidney, adrenal, bone
3. Permanent cells: CNS, skeletal muscle

• G1: Gap phase.
  Variation by lenght of cell's cycle is determined mostly by the lenght of time it spends in G1
  Retinoblastoma gene (Rb1) serves as restriction point (for cyclin dependent kinase)
  p53 gene produces p53 protein which arrests cell cycle by increasing concentration of p31 (cyclin-dependent kinase inhibitor)
  G0 - resting phase
• S: Synthesis phase
  Cell wall, cytoplasm, nuclear proteins made
• G2: Second gap phase
• M: Mitosis

Oncogene

Abberant genes which were previously important in the regulation of the cell cycle

Mechanisms of oncogenesis

1. Amplification: increases copies of proto-oncogene result in excessive activity
2. Point mutation: conversion of proto-oncogene into permanently active gene
3. Incorporation of new promoter: viruses can insert promotor sequences into human DNA
4. Incorpation of enhancers
5. Translocation of chromosomal material

Mechanisms of action

1. Signal transduction pathway effects
2. Regulation of nuclear activity
3. Growth factors / receptors
4. Inhibition of apoptosis