# Mitosis

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```					Cell Growth and Reproduction
(Mitosis)

How a Parent cell divides to form
2 new Daughter cells
Cell Growth
• As an organism grows, do its cells increase in
size OR do cells divide to produce new
daughter cells?
• 2 limits to Cell Growth (increase in size)
– More demands cell places on its DNA (to
amounts at right place at right time)
– More difficulty controlling the trafficking of
nutrients/wastes into and out of cells
• When cell is small, information stored
within DNA able to meet its needs
• As cell increases in size, no extra copies
of DNA produced
• Therefore, if cell grows without limits, a
“information crisis” would result
Trafficking of Materials
• Rate of exchange of materials is
affected by surface area of cell (or total
area of its cell membrane)
• YET, Rate at which nutrients
used/waste products produced
dependent upon cell’s volume
Trafficking of Materials
(cont’d)
• Thought experiment:
• Cell is shaped like a cube
• If length = 1 cm; SA = 6 cm2 (L x W x # sides)
• THEREFORE, volume = 1 cm3 (L x W x H/D)
• RATIO SA/V = 6:1

• If length = 2 cm; SA = 24 cm2
• Volume = 8 cm3
• Ratio SA/V = 3:1
Trafficking of Nutrients
(cont’d)
• NOW, Length = 3 cm; SA = ? cm
• Volume = ?
• Ratio SA/V = ?

• Length = 4 cm; SA ? Volume ? Ratio ?

• TREND is: Volume is increasing at a faster rate, as
compared to the Surface Area of the cell (ratio is
decreasing); SOLUTION?
Surface Area:Volume Ratio
Graphic Representation-Ratio
Final Problem
• If cell size doubles (from 1 cm in size to 2
cm), the cell requires 8x more nutrients and
would have 8x more waste to excrete
• YET, only have a 4x increase in SA; the
plasma membrane does not have enough SA
through which materials can diffuse
• Cells either starve to death or become
poisoned from buildup of waste products
Cell Division
• Before cell becomes too large, it MUST divide
to form 2 “daughter cells”
• Before cell division occurs, the cell
replicates/copies its DNA.
• WHY? (2 reasons)
• Goal: to produce 2 daughter cells identical to
the parent cell
• Direction: to grow in size AND to replace
Chromosomes
• DNA is carried within
chromosomes (DNA + proteins)
• Each organism has a specific
number of chromosomes in
each cell (Fruit fly = 8, Human
= 46, Cat = 38 and Mouse = 40)
• Chromosomes only become
visible at the beginning of cell
division
Chromosomes (cont’d)
• Terminology:
• At the start of cell division, each chromosome
doubles to form TWO SISTER CHROMATIDS
• Each pair of sister chromatids are attached at
an area referred to as a CENTROMERE; usually
attachment site is near the center of the sister
chromatid pair
• Therefore, each human cell is composed of 46
chromosomes, each of which consists of a pair
of sister chromatids
The Cell Cycle
• A series of events cells proceed through
as they grow and develop
• Interphase- the “in-between” period of
growth from round of mitosis to the
next
• During the cell cycle, cell grows,
prepares for cell division and divides to
form two daughter cells
The Cell Cycle
The Cell Cycle
• 4 phases of cell division:
– M phase- Mitosis/Cytokinesis (shortest
phase)
– G1 Phase = Gap 1; all the events that
occur as a cell prepares to copy its
chromosomes
– S phase- Chromosome copying
– G2 = Gap 2; all the preparation for
Mitosis/Cytokinesis + Centrioles double
Student Review Questions

• What is a chromosome?
• What is a centromere?
• What are sister chromatids?

• What are the 4 parts of the Cell Cycle?
• What occurs in each step?
Mitosis-(Nuclear Division) -
Interphase
• Each chromosome
doubles to form 2 sister
chromatids
• Each centriole doubles
as well
• Chromatin- DNA
wrapped around
proteins; Diffuse
material within nucleus
• Cell increases in size
• Cellular activities for life
occur here
Mitosis-Prophase
• 50-60% of total time
• Chromosomes
become
visible/condense
• Nuclear membrane
breaks
down/nucleolus
disappears
Mitosis-Prophase

• Centrioles separate
to opposite
poles/ends of cell
• Microtubules extend
from the centrioles
to form ASTER-
star-shaped
structure located at
poles of cell
Mitosis-Prophase

• Other Microtubule
fibers go from
pole to pole
forming a
football-shaped
structure =
Spindle
Mitosis-Metaphase
• Chromosomes line
up across the
Metaphase plate
• Microtubules/spindle
fibers connect the
centromeres of each
chromatid pair to
the centrioles at the
“poles” of the cell
Mitosis-Anaphase
• Sister chromatids
separate to opposite
poles of the cell
• The centromere of each
pair of chromatids
divides, separating into
individual chromosomes
• Centrioles “reel in” each
member of the sister
chromatid pair by
shortening the spindle
fibers
Mitosis-Telophase
• Nuclear membrane
reforms around
chromosomes
• Chromosomes de-
condense forming
chromatin
• Spindle fibers
disappear; nucleolus
reappears
Cytokinesis-Cytoplasm Division

• Cell membrane
invaginates (drawn
inward) until the
cytoplasm is pinched
into 2 equal parts
• Each part contains a
nucleus and organelles
• Plant cells: cell plate
forms; midway between
dividing nuclei
Results of Mitosis

• In both animal and plant cells, Mitosis
results in the formation of two daughter
cells identical to each other and to the
parent cell which they came from
• The resulting daughter cells enter
Interphase
Student Review Questions

• What is the goal of Mitosis?
• Briefly describe the events that occur
during each step of Mitosis:
– Interphase            Anaphase
– Prophase              Telophase
– Metaphase             Cytokinesis
Length of Time for Mitosis

• Length of time needed for cell to divide
completely depends on:
– the kind of cell
– the environmental conditions under which
it exists
– Most cells complete mitosis in 1-2 hours
– Mammalian cells grown in a laboratory may
require 24 hours to complete one cell
division
Plant-Interphase
• Cell prepares for
division by:
 replicating
DNA and
organelles
 increasing
cell size
Plant-Prophase
• Nuclear membrane
/nucleolus disappears
• Chromatin/
chromosomes condense
• Spindle fibers/MT
elongate from migrating
“anchor proteins”
Plant-Metaphase
• aligning
chromosomes at cell
equator
• attaching spindle
fibers from each
new daughter cell
pole to each
chromosome at the
centromere
Plant-Anaphase
• spindle fibers pull
chromosomes apart
• one-half of each
chromosome
(chromatid) moves
to a new daughter
cell
Plant-Telophase
• DNA decondenses
and two nuclei form
• new cell wall (cell
plate) appears
between the two
nuclei to form two
new daughter cells
Plant-Cytokinesis
• Cell plate forms
midway between
divided nuclei
develops into
separating
membrane
• Cell wall forms
within cell plate
Cell Cycle Regulation
• Different cell types grow and divide at varying rates
(muscle and nerve cells infrequently vs. skin and
digestive tract constantly throughout life)
• Controls : contact inhibition
– Cyclin proteins-regulate timing of cell cycle
– Cyclin-dependent Kinases (cdk) (adds phosphate
to a protein), along with cyclins, are major control
switches for the cell cycle, causing the cell to
move from G1 to S or G2 to M.
– cdk inhibitors(cdk-I)- remove phosphate
group/switch off cell cycle progression
Cell Cycle Regulators (cont’d)

• Internal regulators- proteins that
respond to internal/within cell signals
(cdk/cyclins/cdk-I))
• External - respond to external/outside
cell signals; speed up or slow down rate
of mitosis (oncogenes/tumor suppressor
genes-the “accelerators and brakes” )
Cell Cycle Regulators
Cell Cycle Regulation

• MPF (Maturation Promoting Factor) includes the CdK
and cyclins that triggers progression through the cell
cycle.
• p27 is a protein that binds to cyclin and cdk blocking
entry into S phase. Recent research ( Nature Medicine
3, 152 (1997)) suggests that breast cancer prognosis
is determined by p27 levels. Reduced levels of p27
predict a poor outcome for breast cancer patients.
P53-The “Guardian of the
Genome”
• p53 is a protein that functions to block the cell cycle
if the DNA is damaged. If the damage is severe this
protein can cause apoptosis (cell death).
– p53 levels are increased in damaged cells.
This allows time to repair DNA by blocking
the cell cycle.
– A p53 mutation is the most frequent
mutation leading to cancer. An extreme
case of this is Li Fraumeni syndrome, where
a genetic defect in p53 leads to a high
frequency of cancer in affected individuals
Normal Cell Characteristics

Reproduce themselves exactly
 Stop reproducing at the right time
 Stick together in the right place
 Self destruct if they are damaged
 Become specialized or 'mature'
Cancer
• Uncontrolled cell growth
• Gene- segment of DNA
that controls the
production of a protein
• Changes in one or more
genes that produce
enzymes (proteins!)
involved in control of
cell cycle
How Cancer Cells are different
 They carry on reproducing
 They don't obey signals from other
neighboring cells
 They don't stick together
 They don't become specialized, but stay
immature
 They don't die if they move to another part of
the body
They don’t stop reproducing
Cancer (cont’d)

• Characteristics include: lack of contact
inhibition, “pile on”/cell growth and
ability to grow in suspension
• Cancer cells do not respond to signals
regulating cell growth; tumor formation
results (masses of cells that damage
surrounding tissues; deprive normal
cells of nutrients)
Cancer cells do not stick together
Cancer (cont’d)

• Tumor types: benign vs. malignant
• Tumor metastasis
• Second leading cause of death in U.S.
(behind Cardiovascular disease)
• Nearly half of all men and over one
third of all women will develop cancer
Tumor Metastasis
Cancer (cont’d)
• Most prevalent: in females breast and ovarian
vs. Males-prostate, testicular and colon;
BOTH: LUNG!
• These abnormal and cancerous cells develop
because of damage to DNA that cannot be
repaired. Sometimes the cancer is inherited
through the DNA but more often the damage
to the DNA is caused by exposure to
something in the environment.
Cancer -Risk Factors

• combination of genetics/family history
and environmental exposure
• YOUR GENES- > 50% of all cancers have a
defect in p53- a tumor suppressor protein
microwaves), viruses, tobacco, air and
water pollution
• THINK: Domino Effect!
Carcinogens/Risk Factors

• changes in the body which then leads
to the development of cancer
• Hormone levels
• asbestos (and other fine particulate
matter), nickel compounds, arsenic,
Common Risk Factors
 Growing older
 Tobacco
 Sunlight
 Certain chemicals and other substances
 Some viruses and bacteria
 Certain hormones
 Family history of cancer
 Alcohol
 Poor diet, lack of physical activity, or being overweight
Some Thoughts on Cancer

• Not everything causes cancer.
• Cancer is not caused by an injury, such as a bump or bruise.
Cancer is not contagious.
• Although being infected with certain viruses or bacteria may
increase the risk of some types of cancer, no one can "catch"
cancer from another person.
• Having one or more risk factors does not mean that you will get
cancer. Most people who have risk factors never develop
cancer.
•   Some people are more sensitive than others to the known risk
factors.
Cancer in the Scalp
Chest X-Ray-Lung Cancer
Cancer-Symptoms
• unexplained weight loss
• Developing a fever; disease or the treatment
can affect the immune system and inhibit its
ability to resist infection
• Fatigue
• unexplained pain
• Skin changes darkening, yellowing (jaundice),
reddening, itching or even excessive hair
growth.
Cancer-Early Detection

• The sooner the cancer is detected and
treated, the better an individual’s
chance of making a full recovery
• A person’s chance of detecting the
cancer early is greatly improved if you
incur regular physicals and undertake
regular self examinations
Cancer-Early Detection
• Self examinations for the breast
• Physical examinations by a doctor or other health
professional for the breast, colon, thyroid and skin,
• Laboratory tests like a Pap test, prostate specific
antigen (PSA) blood test and mammography
• Most effective strategy for early detection is to use a
combination of two or more early detection
strategies.
Cancer -Prevention

• eating healthy and maintaining a
nutritional diet by limiting your
consumption of fried foods, alcohol, and
refined carbohydrates
• choose white meat over red meat and
eat whole grain foods rather than
processed ones.
• NO TRANS-FATS (LDL Bad; HDL GOOD)
Cancer -Prevention

• It also helps to be physically fit by
exercising at least an hour a day and
walking as much as you can or joining a
team.
Cancer -Prevention

• exercise + healthy lifestyle (diet) + DO NOT
SMOKE!
• Diet: low in fat and high in fiber content
(fruits, vegetables, grain products)
• Vitamins and minerals (A, C, E, Calcium and
carotenoids-in orange and yellow vegetables)
Cancer-Chemotherapy
• Used to treat metastasized cancer cells
• Can be used to cure cancer, to prevent it
from spreading, to slow the growth of the
cancer, to destroy cancerous cells that have
moved to other parts of the body and to help
relieve some of the symptoms caused by the
cancer.
• Purpose will actually serve all depends on
the type of cancer you have and its stage of
development.
• uses ionizing radiation to kill cancer cells and
reduce the size of tumors.
• Works by destroying the cells in the area that
is being targeting by injuring their genetic
material, thereby making it impossible for
them to grow and divide
• tries to damage as many, if not all, of the
cancer cells as possible while limited the
harm to the nearby healthy cells and tissue.
Immunotherapy
• Immune system (body’s natural defense mechanism)
is an important element in the body’s response to
cancer
• Some forms of cancer develop when the immune
system is not able to destroy the cancerous cells or
inhibit their growth.
• work in a couple of ways such as interfering with the
growth of the cancer cells, indirectly helping the
healthy immune cells to control the cancer or
repairing normal cells that were damaged by the
cancer treatment.
Surgery Treatment
• It can cure the cancer if the cancer can be
completely removed, if a border of healthy tissue that
is cancer cell free can also be removed with the
cancer and if the cancer has not spread before the
surgery!
• During the surgery, the main lymphatic nodes and
lymph nodes that are closest to the cancer or the
organ where the cancer cells are allocated will be
removed;these are the places where the cancer is
Papilloma Virus and Cancer

 Two human papilloma viruses that infect the
reproductive organs (sexually transmitted disease)
 “Pediatricians, gynecologists and even health insurers
all call Gardasil (Merck and Co.), the first vaccine to
prevent cervical cancer, a big medical advance.” Yet,
“get state legislatures to require 11- and 12-year-old
girls to get the three-dose vaccine as a requirement
for school attendance?” AND “Promote sexual
activity?”
 Vaccines mandated for school attendance “usually
are for diseases easily spread through casual contact,
such as measles and mumps.”
Viruses and Cancer
 Hepatitis B and Hepatitis C viruses, which infect
the liver and are closely associated with liver cancer
(probably because of the chronic inflammation they
produce)
 Some herpes viruses such as the Epstein-Barr
virus (implicated in Burkitt's lymphoma) and KSHV
that is associated with Kaposi's sarcoma (a
malignancy frequently seen in the late stages of
AIDS)
 two human T-cell leukemia viruses, HTLV-1 and
HTLV-2
Cancer-Summary
• Remember: To get Cancer, many dominoes
have to fall!
(http://www.pbs.org/wgbh/nova/cancer/gro
ws.html)
• Prevention is Key
– Diet
– Exercise
– Yearly check-ups + self examination
– NO SMOKING!

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 views: 29 posted: 12/19/2011 language: English pages: 76