Transcript The Genetics of Cancer

The Genetics of Cancer
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Cancer in the media
Human and Cancer
Life and adaptation
cell division
cancer is a disease of the cell cycle
Cont. Of RNA
Synth. Of RNA &
proteins
G1 checkpoint
DNA damage or broken
Control
system
G1
M
G2
Chromosomes are
attached to the spindle
M checkpoint
In complete DNA replication
G2 checkpoint
S
G0
G1 checkpoint
G1
If a cell receives a go-ahead
signal at the G1 checkpoint, the
cell continues on in the cell
cycle.
G1
If a cell does not receive a goahead signal at the G1
checkpoint, the cell exits the cell
cycle and goes into G0, a
nondividing state.
Unlimited number of cell divisions.
Growth without external signals.
Failure to respond to 'stop' signals
Avoidance of cell death.
The ability to leave the original
tumor location and form a new
tumor, or metastasis.
Cancer terminology
Classification by tissue type:
• carcinoma
• Myeloid
epithelial cell
90% of all tumours
derived from ectoderm (mostly) or endoderm (some) •
• sarcoma
connective tissue
2% of all tumours
derived from mesoderm
• leukaemia
circulatory or lymphatic
8% of all tumours
derived from mesoderm
blood cell
Lymphoid
lymphocytes or macrophages
• Central nervous system
cancers of the brain
Main Features of Benign and
Malignant Tumors
Cancer Spreads Step-by-Step
A Common Type of Colorectal Cancer May
Develop by These Steps
Types of genes which may mutate to cause cancer:
• Tumor suppressor genes
– Stop cell growth and division; prevent cancer
formation
– May prevent expression of oncogenes
– Retinoblastoma: only one functional copy of a
tumor suppressor gene on chromosome 13
– BRCA1 and BRCA2
– p53: codes for a regulatory protein that turns off cell
division when the cell is stressed or damaged
Types of cancer genes
Type of gene
Normal function
Mutated function
Types of proteins
Oncogene
Promotes division
Promotes division abnormal time or
cell type
Growth factors
Tumor
Suppresses cell
suppressor gene division
Fails to suppress
division
Checkpoint
molecules
DNA repair
gene mutation
Fail to repair DNA
mutations
Enzymes for
mismatch or excision
repair
Repair DNA
mutations
Tumour suppressor genes
• The gene’s normal function is to regulate cell
division. Both alleles need to be mutated or removed
in order to lose the gene activity.
• The first mutation may be inherited or somatic.
• The second mutation will often be a gross event
leading to loss of heterozygosity in the surrounding
area.
Oncogenes
• Cellular oncogene c-onc
• Viral oncogene v-onc
• Proto-oncogene, activated by mutation
to c-onc
Proto-oncogene activation
Other Factors Also May Lead to Cancer
• Inherited susceptibility to cancer
– ~5% of cancers
• Viruses
– Viral DNA may be inserted into a host cell’s DNA
• May switch on a proto-oncogene
• May carry oncogenes
Other Factors Also May Lead to Cancer
• Chemical carcinogens
– Carcinogens: cancer-causing substances that can
lead to a mutation in DNA
• Hydrocarbons in cigarette smoke
• Aflatoxin: fungal product
• Radiation
– UV from the sun and tanning lamps
– X-rays: medical and dental
– Radon, cosmic rays, and gamma radiation
Some Industrial Chemicals Linked to Cancer
In the U.S., More than 1 Million People Are
Diagnosed with Cancer Each Year
Biopsy Is the Only Sure Way to
Diagnose Cancer
• Biopsy
– Removal and microscopic examination of tissue
Light Microscope Image Shows Cancerous Cells in
Breast Tissue
Cancer Treatment and Prevention
• When a person is diagnosed with cancer, a
variety of weapons are available to combat it
 Chemotherapy drugs
 Radiation therapy
 Surgery
Chemotherapy and Radiation Kill Cancer
Cells
• Chemotherapy
– Drugs used to kill cancer cells; disrupt some aspect
of cell division
– Toxic to healthy cells; hair, bone marrow,
lymphocytes, and epithelial cells of intestinal lining
– Side effects include hair loss, nausea, vomiting, and
reduced immune responses
– Genetic approach to chemo in the future
Chemotherapy and Radiation Kill Cancer
Cells
• Radiation therapy
– Used when cancer is small or has not
spread
– Radioisotopes used, e.g., Ra-226 and
Co-60
• Chemotherapy and radiation
destroy healthy cells
• More precise treatments
– Monoclonal antibody treatment
– Interferon treatment; limited at
present
Good Lifestyle Choices Can Limit
Cancer Risk
• Avoid tobacco completely
• Maintain a desirable weight; eat a low-fat diet with
plenty of fruits and vegetables
• Drink alcohol in moderation
• Make sure your living and work environment is safe
from carcinogens
• Protect your skin from the sun’s UV rays
This Cancer Cell Is Surrounded by White
Blood Cells
Cancer Causes and Contributing
Factors
What mark have you thought to leave after?
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