Why mitotic cell cycle tightly regulated?
cell cycle tightly regulated as it is important for normal cell division, development > cell cycle controlled by 3 checkpoints; G1, G2 & M checkpoint determine if cell cycle can proceed > checkpoints ensure key processes such as DNA replication is accurate/ bring about DNA repair mechanisms if required > prevents dysregulation of checkpoints of cell division, prevents excessive cell cycle progression & uncontrolled cell division which leads to tumour formation & possibly cancer
How uncontrolled cell division arises from loss of fn mutation in TSG p53?
loss of fn mutation in BOTH copies of p53 gene results in non-functional p53 protein > disrupts ability of cell to arrest cell cycle/activate DNA repair/trigger apoptosis, leading to uncontrolled cell division
How uncontrolled cell division arises from gain of fn mutation in POG ras?
gain of fn mutation in 1 copy of ras gene results in excessive amounts/hyperactive/degradation-resistant Ras protein > leads to uncontrolled cell division; Ras protein increases cell division even in absence of growth factors
Outline the development of cancer as a result of a causative agent.
development of cancer is multi-step process, requires accumulation of mutations in single cell, angiogenesis & metastasis >
causative agent causes gene mutations(bp sub/addition/deletion) in genes controlling checkpoint of cell cycle >
GOFM in 1 copy of POG results in excessive amounts of protein products leads to uncontrolled cell division OR
LOFM in both copies of TSG results in non-functional protein products which disrupts ability of cell to arrest cell cycle leads to uncontrolled cell division >
mutations in same somatic cell results in rate of cell division>rate of cell death, leading to uncontrolled cell division & tumour formation >
angiogenesis, growth of new blood vessels occurs within tumour to transport O2, nutrients to support growth of tumour >
cells of tumour invade surrounding tissue & metastasise to other sites, tumour considered malignant; cancer has developed
Define proto-oncogene
gene which codes for proteins involved in regulation of normal cell growth, cell division >
when mutated, oncogene >
oncogene expression leads to increase in amount of POG protein/ intrinsic activity of protein(hyperactive/degradation resistant)
Define tumour supressor gene
gene which codes for proteins that inhibit cell division, help to prevent uncontrolled cell growth, cell division >
protein products activate cell cycle arrest/DNA repair/apoptosis >
when mutated, decrease in activity of TS protein
What are the causative causes of cancer?
1. genetic predisposition
2. chemical carcinogens SUCH AS tobacco, ethidium bromide, asbestos
3. ionising radiation SUCH AS nuclear radiation, X-rays, gamma rays, UV radiation
4. age, loss of immunity