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Cancer and the Cell Cycle. Chapter 2. Cancer is a complication of being a multiple-cell organism. The price we pay for being multicellular. What causes cancer?. Cancer cells are abnormal cells that arise from the body’s normal tissue through mutations. - PowerPoint PPT Presentation
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Cancer and the Cell Cycle
Chapter 2
The price we pay for being multicellular
Cancer is a complication of being a multiple-cell organism.
What causes cancer?
Cancer cells are abnormal cells that arise from the body’s normal tissue through mutations.
Mutated genes that cause cancer are called oncogenes.
It is thought that several mutations need to occur to give rise to cancer
Cells that are old or not functioning properly normally self destruct and are replaced by new cells.
However, cancerous cells do not self destruct and continue to divide rapidly producing millions of new cancerous cells.
Cancer Causing Agents
Ionizing radiation Chemicals in the envionment Virus infection http://
www.nih.gov/news/pr/jan2005/niehs-31.htm
Hereditary predisposition – Some families are more susceptible to getting certain cancers. Remember you can’t inherit cancer its just that you maybe more susceptible to getting it.
Central Points
Cancer involves uncontrolled cell division Mutations in certain types of genes such as
proto-onco genes and tumor supressor genes may lead to cancer. When genes are mutated and become cancer causing they are known as oncogenes.
Cancer is a disease that involves problems in the control of the cell cycle.
Breast, colon, and lung cancer are common types of cancer.
Benign or malignant? Benign tumours do not spread from their site of origin,
but can crowd out (squash) surrounding cells.
Malignant tumours can spread from the original site and cause secondary tumors. This is called metastasis. They interfere with neighbouring cells and can block blood vessels, the gut, glands, lungs etc.
Why are secondary tumours so bad?
Both types of tumour can tire the body out as they both need a huge amount of nutrients to sustain the rapid growth and division of the cells.
Cancer cells are abnormal cells that arise from the body’s normal tissue.
Environmental causes of cancer are being studied. Lawsuits have addressed smoking as a cause of cancer for example.
Central Points
Are malignant tumors monoclonal in origin? That is derived from a single ancestral cell that underwent conversion from a normal cell to a cancerous state? Or are malignant tumors polyoclonal in origin that is many individual cells become cancerous and the resulting tumor represents the descendents of these original cells.
Monoclonal or polyclonal
Cancer Cells
Animation: How Cells Reproduce
Cancer video
HHMI video
How Is Genetics Involved?
Two classes of genes: Oncogenes and tumor suppressor genes
Proto-oncogenes: control cell division
Tumor suppressor genes turn off cell division
Mutated alleles, oncogenes, and tumor suppressor genes cause cells to divide uncontrollably
Mutations in Tumor Suppressor Genes
1st mutation (susceptible carrier)
Active oncogene
No brakes!
Active oncogene
Normal genes (regulate cell growth)
Tumor suppressor genes
2nd mutation or loss (leads to cancer)
Tumor suppressor genes
No brakes!
Cancer-Causing Mutations
Exposure to environmental agents, virus, or lifestyle changes may cause a mutation
Certain virus infections can transform the cell
Human papillomavirus (HPV): Viral proteins interact with cell proteins, cause cervical cancer
Mistakes in DNA replication also cause mutations
4Cell
division
Mitosis
3DNA
repair
G21
Cell grows,
doubles in size
G1
S
2Chromosome
duplication
G2/M checkpoint
G1/S checkpoint
Regulation of Cell Cycle
G1/S checkpoint
G2/M checkpoint
Tumor suppressor genes and proto-oncogenes control these checkpoints• Tumor suppressor genes turn off or decrease rate
of cell division • Proto-oncogenes turn on or increase rate
Signal Transduction
In normal cells, signals from outside cell can• Activate tumor suppressor genes (turning off cell
division) or• Activate proto-oncogenes (turning on cell
division)
Signals can be proteins, hormones, or nerve signals
May include steroids, pollutants, and other molecules
Process of Signal Transduction
Signal binds to a receptor in plasma membrane
Binding sets off series of interactions inside cell
Signal molecule may remain outside cell
Binding of signal changes shape of receptor and allows it to transmit signal to other proteins
May alter gene expression
Outside cell
Receptor
Plasma membrane
Cytoplasm
Nucleus
Changes in gene expression
Signal molecule
Signal–receptor binding
Cellular response
Protein molecules
Ras Signaling This is a detailed view of Ras interactions in pathways leading to:• cell proliferation• cell survival• differentiation• cell cycle control• cell motility• tumorigenesis
Proto-Oncogene RAS (1)
Produces RAS protein that:• Attaches to inside of plasma membrane• Is part of a pathway that turns on cell division• Is signaled by growth factors from outside the cell• Changes shape and switches on when activated• Transfers signal to another protein in pathway• Changes shape again after signal transmitted,
switches off (inactive)
Proto-Oncogene RAS (2)
RAS mutations in many types of cancer, including colon, lung, pancreatic, and stomach cancer
Mutant RAS stuck “on” and produces uncontrolled cell division
Cancer Genes on other Chromosomes
Environmental Factors and Populations
Determine types of cancer populations may develop
Many forms of cancer related to: • Physical surroundings• Personal behavior• Or both
At least 50% of all cancer can be attributed to some type of environmental factor
Spotlight on Ethics: HeLa Cell Line (1)
In 1951, cervical cells removed from Henrietta Lacks during biopsy
She died from cervical cancer
Cells maintained in vitro (in the lab) and used for worldwide scientific study
HeLa cells immortal because they can divide an
unlimited number of times in a laboratory
Spotlight on Ethics: HeLa Cell Line (2)
Originally grown without Lacks’ knowledge or permission and later sold to medical schools
Have been used for commercial products: HPV vaccine
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