Ch. 5 Cell DivisionPart 3

Mitosis vs. Meiosis Mitosis

Results in the production of two genetically identical DIPLOID cells

Daughter cells have sets of chromosomes identical to each other and to parent cell

MITOSIS allows body to grow and replace other cells

Asexual reproduction Meiosis

Results in four genetically different HAPLOID cells MEIOSIS is how sexually reproducing organisms

make gametes

Alternation of Generation in Plants Organism changes between haploid life

stages and diploid life stages Sporophyte (diploid stage)

Uses meiosis to produces haploid “spores” that it releases

Gametophyte (haploid stage) Divides by mitosis and produces gametes Male gamete will find a female gamete to

fertilize; together they create the next, new generation that is diploid (new sporophyte)

Sporophyte and gametophyte are sometimes in same organism or sometimes they are completely separate organisms

Telomeres Composition:

Made of DNA and proteins Short base sequences repeated many times (multiple repeat

sequences) One side of DNA = lots of GUANINE Other side of DNA = lots of CYTOSINE (complementary base pair

of G) Function:

Prevent loss of genes during cell division & allow continued replication of cell

To ensure that when DNA is replicated, the ends of the DNA molecule are included in replication

Copying enzyme in DNA replication does NOT run to the end of the DNA molecule

That end piece of DNA is NOT replicated; it is lost Loss of vital genes = cell death

Every time a cell divides, a small section of DNA at the end of the molecule is lost (not ALL cells do this)

To prevent complete loss, BASES are added to DNA during every replication by enzyme TELOMERSE

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 Potency extent of power of stem cell to produce

different cell types Totipotent stem cells can produce any type of cell

Ex. Zygote & cells up to 16-cell stage of development

Pluripotent cells that cannot become specialized to form placenta BUT can still differentiate into all cells that lead to development of organism Ex. Embryonic stem cells

Multipotent stem cells that have lost most of their potency and can only differentiate into a few types of different cells Ex. Adult stem cells and Bone Marrow Cells

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

Cancer Most common disease in developed countries Accounts for 1 in 4 deaths in developed

countries More than 100 different forms of cancer Over 200 different forms of cancer Lung cancer

One in 16 deaths in UK in 2006

Most common cancer in men Prostate cancer (24% of cases)

Most common form of cancer in women Breast (31% of cases)

Cancer A disease that is the result of uncontrolled

mitosis Cancer cells show abnormal changes in

shape 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”

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 ANGIOGENESIS development of new blood vessels to new tissue

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

Cancer Mutation can occur in one cell Mutation can be passed down to all of

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 Anything agent that causes cancer These can 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

Radon naturally occurring radioactive gas

found at low levels in most soil

produced in the soil when the element uranium starts to break down

Health effects of high radon levels increased cases of lung cancer

found in underground uranium miners in the United States and around the world

Radon gas seeps into cracks in the foundation of homes from surrounding soil about 1 in 20 homes has elevated

radon levels Research estimates that about

20,000 lung cancer deaths every year may be linked to radon exposures in homes

Nuclear Fall Out Cause Caused by:

Atomic bombs above-ground atomic bomb testing increase cancer risk.

People affected by ionizing radiation:

People in Japan at the end of World War II (atomic bomb)

People living near nuclear testing sites in Nevada in the late 1950s and early 1960s

People near the site of the Chernobyl nuclear power plant accident in the former Soviet Union in 1986

Japanese atomic bomb survivors increased rates of cancers of the breast, thyroid,

lung, stomach, and other organs.

People, especially children, exposed to iodine-131 (one form of radioactive iodine) from US above-ground nuclear testing and from the Chernobyl accident, have an increased risk of thyroid cancer

Nuclear Medicine and X-Ray X-rays, mammograms, and

radiation therapy all involve exposure to ionizing radiation

Chest X-ray little exposure to radiation

Studies have not shown an elevated cancer risk associated with X-rays taken to diagnose a disease or condition

Exception: children whose mothers received X-rays

while pregnant increased risks of leukemia and other types

of cancers

X-rays to diagnose a condition in pregnant women NOT recommended.

Radiation Therapy Radiation to treat a

conditions (cancer or ringworm)

likely to increase cancer risk

Radiation to treat conditions of the head and neck have an increased risk of: thyroid cancer tumors of the head

and neck

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 Asbestos

group of minerals that occur naturally in the environment as bundles of fibers that can be separated into thin, durable threads

resistant to heat, fire, and chemicals and do not conduct electricity Widely used in many industries. Chemically, asbestos minerals are silicate compounds

contain atoms of silicon and oxygen in their molecular structure

Dioxines Chemical compounds that share certain chemical structures and biological

characteristics Members of three closely related families

chlorinated dibenzo-p-dioxins (CDDs) chlorinated dibenzofurans (CDFs) polychlorinated biphenyls (PCBs)

Certain dyes (aniline) are well-known carcinogens A group of chemicals called arylamines are known to cause bladder cancer banned in the UK for about 20 years

Asbestos and other chemicals Asbestos is linked to increased

risks of : lung cancer mesothelioma

a rare cancer of the lining of the lung and abdominal cavity

asbestos was widely used in construction, but its use has been restricted workers employed in construction,

electrical work, or carpentry may still be exposed through renovations or asbestos-removal projects

Other fibers and dusts (including silica dust and wood dust) can increase the risks of cancers of the lung, nasal cavities, and sinuses

Dioxins byproducts of paper

bleaching, smelting, and waste incineration

widespread in the environment break down very slowly

accumulate in fat cells most exposure to

dioxins comes from eating dairy products, fish, and meat

Aniline (dye) Benzidine (Aniline) associated with cancer since

the 1920s used in the production of dyes

for paper, textiles, and leather Exposure to these dyed

products is not hazardous

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 The Epstein-Barr virus has been

linked to Burkitt's lymphoma 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

RNA Viruses Human T lymphotrophic virus type

1 (HTLV-I), a retrovirus, has been linked to T-cell leukemia

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

susceptibility to the factors that can cause the disease 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

Breast Cancer BRCA1 and BRCA2 human

genes belong to a class of genes known as

tumor suppressors

In normal cells: help ensure the stability of the cell’s

genetic material (DNA) help prevent uncontrolled cell growth Mutation of these genes has been

linked to the development of hereditary breast and ovarian cancer.

Mutation linked to the development of hereditary breast and ovarian cancer

BRCA1 and BRCA2 stand for breast cancer susceptibility gene 1 breast cancer susceptibility gene 2