Cell Cycle Checkpoints
A cell cycle contains numerous checkpoints that ensure
the fidelity and viability of continued cell divisions
G1 checkpoint
- Monitors potential growth conditions (nutrients, etc.)
- Assesses level of DNA damage (from UV, etc.)
G2 checkpoint
- Monitors state of pre-mitotic cell (suitable size, etc.)
- Identifies and repairs any DNA replication errors
Metaphase checkpoint
- Ensures proper alignment (prevents aneuploidy)
Cyclins
proteins that control progression of the cell cycle
Cancer
Cancers are diseases caused by uncontrolled cell division
Tumors
Tumor cells may remain in their original location (benign)
or spread and invade neighboring tissues (malignant)
Cancers can be caused by many different factors:
- Mutagens
- Genetics
Mutagens
Mutagens are agents that change the genetic material of cells
* These agents may be either physical (e.g. UV), chemical
(e.g. arsenic) or biological in origin (e.g. certain viruses)
* Mutagens that cause cancer are classified as carcinogens
Genetics
Most cancers are caused by mutations to two classes of genes:
* Proto-oncogenes stimulate cell growth and proliferation
* Tumor suppressor genes repress cell cycle progression
The death of a cell may occur by one of two mechanisms:
- Necrosis (uncontrolled ‘cell homicide’)
- Apoptosis (programmed ‘cell suicide’)
Necrosis
- The cell loses functional control due to injury, toxins, etc.
- There is a destabilization of the membranes, leading to swelling
- The cell bursts and releases its contents (causing inflammation)
Apoptosis
- It is a controlled event triggered by mitochondrial proteins
- Cell contents are packaged in membranous protrusions (blebs)
- The cell fragments into apoptotic bodies which are recycled
Smoking
There is a strong positive correlation between the
frequency of smoking and the incidence of cancer
* Cigarette smoke contains >60 known carcinogens
