The Cell Cycle and Cancer

Checkpoints in the Cell Cycle In normal healthy cells, there are proteins that send messages to the nucleus to stay in interphase if: Signals from surrounding cells say to not divide DNA has not been replicated or is damaged on certain genes Finite number of divisions – cellular apoptosis

1. Chemical Signals from surrounding cells help tell a cell when to start and stop dividing. There are not enough nutrients to allow proper growth All cellular space is currently covered – called contact inhibition, as all cells only grow to a certain density

2. DNA has not been replicated or is damaged Before a cell divides, the DNA is checked to make sure it has replicated correctly. (If DNA does not copy itself correctly, a gene mutation occurs. DNA replication animation:click on DNA picture

Key Gene Mutations Oncogenes, mutant alleles of a proto-oncogenes Oncogenes encode proteins that stimulate proliferation or inhibit apoptosis Tumor-suppressor genes (TSGs), also called “gatekeepers”, which encode for regulators of various cell-cycle checkpoints “caretakers”, which encode proteins responsible for detecting and repairing mutations

Cell Cycle Controls Timing is controlled by cyclic variations in the concentrations of certain proteins – cyclins Checkpoints are included to stop the cycle in the event of catastrophic damage or incomplete steps.

DNA mutations disrupt the cell cycle. Mutations may be caused by: 1. radiation 2. smoking 3. Pollutants 4. chemicals 5. viruses

3. Finite Number of Divisions The regulated death of a cell that is no longer useful (e.g. white blood cells post-infection) or has lost its ability to function efficiently is called apoptosis. What happens when damage to a cell impairs its ability to commit apoptosis and it divides and divides and divides? You get Cancerous cells

The Beginning of Cancerous Growth National Cancer Institute Understanding Cancer and Related Topics Understanding Cancer The Beginning of Cancerous Growth Cancers grow more quickly where cells divide frequently. Cancerous growths are called tumours. Underlying tissue NCI Web site: http://cancer.gov/cancertopics/understandingcancer

Invasion and Metastasis National Cancer Institute Understanding Cancer and Related Topics Understanding Cancer Invasion and Metastasis Cancer cells can invade surrounding tissues and blood vessels. They can also be transported by the circulatory system to other parts of the body (metastasis). Cancer cells then grow at the new locations. NCI Web site: http://cancer.gov/cancertopics/understandingcancer

METASTASIS The transfer of disease from one organ or part of an organ to another not directly connected with it Video link below: https://www.youtube.com/watch?v=rrMq8uA_6iA&feature=player_embedded

Malignant versus Benign Tumors National Cancer Institute Understanding Cancer and Related Topics Understanding Cancer Malignant versus Benign Tumors Malignant cells invade neighboring tissues, enter blood vessels, and metastasize to different sites. Benign tumor cells grow only locally and cannot spread by invasion or metastasis. Time NCI Web site: http://cancer.gov/cancertopics/understandingcancer

Cancer is a disease of the cell cycle Cancer is a disease of the cell cycle. Some of the body’s cells divide uncontrollably and tumors form. Tumors in Liver Tumor in Colon

While normal cells will stop dividing if there is a mutation in the DNA, cancer cells will continue to divide with mutation.

Due to DNA mutations, cancer cells ignore the chemical signals that start and stop the cell cycle. They also no longer communicate well with neighboring cells

Differences between Benign and Malignant tumors   BENIGN MALIGNANT Often encapsulated Non encapsulated Well differentiated Poorly differentiated Low mitotic rate High mitotic rate Noninvasive Invasive Non-metastasising Metastasising

Why Cancer Is Dangerous National Cancer Institute Understanding Cancer and Related Topics Understanding Cancer Why Cancer Is Dangerous Melanoma (skin cancer) cells can travel through the circulatory system. The cancer that spreads to the liver would be called metastatic melanoma, not liver cancer. Liver Melanoma (initial tumor) NCI Web site: http://cancer.gov/cancertopics/understandingcancer

Cervical Cancer Screening National Cancer Institute Understanding Cancer and Related Topics Understanding Cancer Cervical Cancer Screening Normal Pap smear But even earlier stages of cancer can be detected by screening cells. Biopsies similarly look at cells inside suspected tumours. Normal Pap smear Abnormal Pap smear Abnormal Pap smear NCI Web site: http://cancer.gov/cancertopics/understandingcancer

Cancer Cells Look Different National Cancer Institute Understanding Cancer and Related Topics Understanding Cancer NCI Web site: http://cancer.gov/cancertopics/understandingcancer

SUMMARY Normal Cell Division DNA is replicated properly. 2. Chemical signals start and stop the cell cycle. 3. Cells communicate with each other so they don’t become overcrowded. Cancer Cells Mutations occur in the DNA when it is replicated. 2. Chemical signals that start and stop the cell cycle are ignored. 3. Cells do not communicate with each other and tumors form.

Apoptosis The material of the cell is recycled by the body.