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Mitosis vs. Meiosis
Meiosis
Mitosis
• Non-reproductive cells
• One parent cell makes 2 GENETICALLY
IDENTICAL daughter cells
• Prophase
• Metaphase
• Anaphase
• Telophase
• EXACT COPIES with same # of
chromosomes
• Reproductive cells only (gametes)
• One parent cell makes 4 GENETICALL
DIFFERENT daughter cells with HALF the
number of original chromosomes
• Prophase 1, Metaphase1, Anaphase 1, Telophase
1
• Prophase 2, Metaphase 2, Anaphase 2,
Telophase 2
• PROPHASE 1 CROSSING OVER
• ANAPHASE 1-> HOMOLOGOUS PAIRS
SEPARATE
• ANAPHASE 2 SISTER CHROMATIDS
SEPARATE
Cancer
• Accounts for 1 in 4 deaths in
developed countries
• More than 100 different forms
of cancer
• Lung cancer=1 in 17 of all
deaths in Britain in the 1990’s
• Most common cancer in menlung
• Most common form of cancer in
women-breast
Cancer
• A disease that is the result of uncontrolled mitosis
• Tumor-irregular mass of cells created by uncontrolled mitosis
Origin of Cancer
• Caused by changes in genes that control cell division
• Mutation- a change in any gene
• Not unusual
• Most mutated cells are either crippled in some way that results in their early death or
they are destroyed by the body’s immune system
• Cancer cells bypass both these fates of mutated cells
• Oncogene- term for mutated gene that causes cancer
• Onkos in Greek means “mass” or “Bulk”
Cancer
• Although mutation may have occurred in one cell, it can be passed down to
all of this one cells’ descendents
• By the time it is detected, a typical tumor consists of about a thousand million
cells
• Mutagen
• A factor that brings about any mutation
• Things can be described as mutagenic
• Carcinogen
• Any agent that causes cancer
• These can be described as carcinogenic
• Some mutagens are carcinogenic
• Factors that increase mutation rates (thus cancer) are as follows:
1. Ionizing Radiation
2. Chemical
3. Viral Infections
4. Hereditary predisposition
Ionizing Radiation
• X-rays, gamma rays, particles of a decaying radioactive element
• Creates the formation of damaging ions inside cells that break DNA strands
• UV light also breaks the DNA strands (but it does not cause the formation of ions)
• Depletion of the ozone layer is becoming a concern
• Leads to more UV radiation hitting Earth’s surface=increase risk to skin cancer
Chemicals
• Chemical compounds found in many consumer products
• 25% of all cancers in developed countries are caused by the carcinogens in
tar of tobacco smoke
• Certain dyes (aniline) are well-known carcinogens
Viral Infections
• Viruses are genetic material and protein
• Cancer viruses are estimated to cause 15 to 20 percent of all cancers in humans
• Viruses that cause cancer usually carry oncogenes, or regulatory genes that can
become oncogenes
• The tumor viruses change cells by integrating their genetic material with the host cell’s
DNA via a permanent insertion mechanism
• This differs depending on whether the nucleic acid in the virus is DNA or RNA
• In DNA viruses, the genetic material can be directly inserted into the host's DNA
• RNA viruses must first transcribe RNA to DNA and then insert the genetic material into the host cell's
DNA.
Viruses and Cancer
• DNA Viruses
• RNA Viruses
• The Epstein-Barr virus has been linked to
Burkitt's lymphoma
• Human T lymphotrophic virus type 1
(HTLV-I), a retrovirus, has been linked to
T-cell leukemia
• Infects B cells and epithelial cells
• Causes mononucleosis, but can also
cause a few different types of lymphoma
and nasopharyngeal cancer
• The hepatitis B virus has been linked to
liver cancer in people with chronic
infections
• Human papilloma viruses have been linked
to cervical cancer
• The hepatitis C virus has been linked to
liver cancer in people with chronic
infections
Hereditary disposition
• Genetic link based on studying patterns in family members
• Disease itself is not inherited but susceptibility to the factors that can cause the disease are
inherited
• Some forms of cancer are believed to be caused by the inheritance of one faulty gene
• Example: Retinoblastoma…caused by error on chromosome 13
• Starts in both eyes during childhood and spreads to brain causing blindness and death if left
untreated
Tumors
•
Small groups of tumor cells are called primary growths
•
2 types
• Benign tumors
• Tumors that do not spread from site of origin
• They can compress and displace other tissues,
causing discomfort and even death
• Warts, ovarian cysts, brain tumors
• Malignant (cancerous) tumors
• Dangerous
• Spread throughout the body, invading and destroying
other tissues
• Interfere with normal functioning of the area they
have started to grow
• Mutated cells break off the tumor and enter either the
blood or lymph via vessel formation and spread all
over the body creating secondary growths
• METASTASIS is the spread of cancer from the origin
to other parts of the body
•
most dangerous form of caner…can be very difficult
to find secondary growths and remove them
• Both benign and malignant tumors involve a huge
drain on the human body due to the high demand
for nutrients that is created by the rapid and
continual cell division
Stem Cells
• Cell that can divide an unlimited
number of times by MITOSIS
• After division, each new cell has
potential to:
1. Remain stem cell
2. Differentiate into specialized
cell
Stem Cell Therapy
• Introduction of new adult stem cells into
damaged tissue to treat disease or injury
• Example:
• Bone marrow transplant
• Future goals of SCT:
• Treat:
• Diabetes
• Nerve and muscle damage
• Brain disorders
• New tissue and organ growth