Cell Cycle Clock, Mitosis, and Cancer Biology

Cell Division – Mitosis of a Zygote

The Cell Cycle Clock G0 - Quiescence Work but no Mitosis

The Cell Cycle Control System is like a clock regulated by both internal and external controls has specific checkpoints where the cell cycle stops until a go-ahead signal is received

The Cell Cycle Control System For many cells, the G1 checkpoint is the most important. If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases and divide. If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a non-dividing state called the G0 phase

The Eukaryotic Cell Cycle is Regulated by a Molecular Control System The frequency of cell division varies with the type of cell. Not all cells divide at the same time, for the same reasons, or as frequent as other cells. These differences result from genetic regulation at the molecular level. This controls the RATE and TIMING of cell division.

Contact Inhibition Cells do not normally grow or divide when in contact with other cells. Ex: Cultured cells in a petri dish will divide until they form a layer one cell thick and then stop when make contact w/ other cells. Called contact inhibition of cell growth. Cells can migrate in culture Stop moving when touch other cells due to contact inhibition of cell movement.

Contact inhibition Does not occur in Cancerous Cells Cancerous cells continue growing and moving when they touch other cells. They pile up and they migrate to other parts of the body -- the cancer spreads. Growth Factors Chemical messages that control the cell cycle

Characteristics of Cancer Cells Have lost the genetic ability to stop dividing Cancer is heritable—Cancer cells give rise to cancer cells Immortal Not subject to contact inhibition Metastasize: Spread into other tissues Are De-differentiated less specialized than the cell it came from)

2. Basal cell carcinoma 1. Normal cell growth One daughter differentiates Only one daughter Cell divides Both daughter cells divide Actively dividing cells (basal cells)

Growth Factors Stimulate Cell Division Diffuse through the body making contact with many different cells Bind to Membrane Receptors, like a key fitting into a lock. stimulate a pathway inside cell that leads to cell division. Different cell types are stimulated by different growth factors.

Cancer: It’s all in the Genes Proto-oncogenes: “pre-cancer genes” Genes that code for growth factors Active in actively dividing tissues (e.g. skin) Sometimes mutate into...... Oncogenes: A mutated proto-oncogene Genes that cause cancer Produce too much growth factor Over stimulate mitosis

Tumor Suppressor Genes Code for Proteins that turn off cell division p53 Gene Codes for a protein that stops the cell cycle after G1 Half of all cancers involve a mutation of p53.

The Role of the Environment in Causing Cancer Certain Viruses, toxins, or Radiation may lead to a p53 mutation A 2nd p53 mutation may lead to one of the following cancers Bladder, blood, brain, breast, colon, esophagus, liver, lung, spleen, thyroid, etc.

TMN System T = Tumor Size N = Lymph Node Involvement M = Metastasis

Therapeutic Strategies for Treating Cancer Slash – Surgical Removal Burn – with Radiation Poison – with Chemotherapy Since cancer is uncontrolled cell division, all chemotherapeutic treatments involve the cell cycle. Phase-specific chemotherapies Prevent cells from entering S-phase Block the S-phase Block the M-phase (mitosis)

Cells Affected by Chemotherapy Chemo may affect all dividing cells Which cells divide rapidly? Hair follicle cells Skin cells Cells lining digestive tract Blood stem cells What would be the side effects?

Common Warning Signs of Cancer: C.A.U.T.I.O.N. C - change in bowel or bladder habits A - a sore that does not heal U - unusual bleeding or discharge T - thickening or lump in the breast or any part of the body I - indigestion or difficulty swallowing O - obvious change in a wart or mole N - nagging cough or hoarseness