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CELLULAR
REPRODUCTION
(DIVISION)
Chapter 9
SECTION 9.1 – CELLULAR GROWTH
There is a limit to cell
size….just as there is a limit
to the size of living things
CELL SIZE LIMITATION….
THERE IS A LIMIT TO CELL SIZE!
The key factor that limits cell size is…the ratio of its
surface area to its volume
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Surface area = area covered by the plasma/cell membrane
Volume = the space taken up by the inner contents
As the cell grows its…. VOLUME increases MORE RAPIDLY
than the surface area ….
In other words…the surface area to to volume ratio decreases.
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This means…the cell might have difficulty supplying nutrients and
expelling wastes
By remaining small…cells have a higher ratio of surface area to volume and
can sustain themselves more easily
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Cells remain small to maximize…. the ability of diffusion to transport
nutrients and wastes
Small cells maintain…. more efficient transport systems
Cell size also affects the ability of a cell to…communicate
instructions for cellular functions
The smaller the cell the more efficient it will be!
Cells grow until they reach their size limit, then they divide (or die)!
THE CELL CYCLE
Once a cell reaches its size limit (maximum) something must happen – either….
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it will stop growing or
it will divide or
it will die
Most cells will….eventually divide
When a cell divides it is called… CELL DIVISION or CELL REPRODUCTION
CELL DIVISION does 2 things…
 not only …prevents the cell from becoming too large
 but it also…is the way the cell reproduces
THE CELL CYCLE
Cells reproduce by a cycle of growing and dividing called the… CELL CYCLE
 each time a single cell goes through one complete cycle it becomes…. 2 cells
 when the cell cycle is repeated again and again, the result is ….a continuous
production of new cells
 there are 3 main stages of the cell cycle: interphase, mitosis, cytokinesis
THE CELL CYCLE
Interphase – the cell grows, carries out cellular functions and copies its DNA
 Mitosis – the cell’s nucleus and nuclear material divide
 Cytokinesis – the cell’s cytoplasm divides, creating a new cell
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DURATION OF THE CELL CYCLE…VARIES…
depending on the (type) of cell that is dividing….
 some eukaryotic cells might complete the cycle in as few as
8 minutes, others might take up to 1 year
 for most normal, animals cells, the cell cycle takes approximately
12-24 hours
INTERPHASE…the stage during which….
 the cell…grows and develops into a mature,
functioning cell
 replicates/duplicates (makes copies) …of its DNA
(genetic material)
 is divided into 3 stages/phases – G1, S, G2
G1 (or Gap 1)
 is the period….immediately after a cell divides
 during G1…A cell is growing, Carrying out normal cell functions and
Prepares to replicate DNA
 some cells, such as muscle and nerve cells, exit the cell cycle at this
point and do not divide again
S (or Synthesis)
 is the period when the cell copies its DNA in preparation for cell division
 chromosomes – structures that contain the genetic material
 chromatin – relaxed form of DNA in the cell’s nucleus
 the cell also takes inventory and makes sure it is ready to continue
G2 (or Gap 2)
 follows the S stage and is the period when the cell prepares for
the division of its nucleus
When the activities (of interphase)
are completed, the stages of
mitosis and cytokinesis will follow
PROKARYOTIC (SIMPLE) CELLS - BACTERIA,
DO NOT UNDERGO CELL DIVISION IN THE
SAME WAY AS EUKARYOTIC CELLS
prokaryotic cells reproduce
by Binary Fission….
1. single, circular shaped
chromosome (DNA)
copies itself
2. the cell splits into 2 cells
EUKARYOTIC CELL DIVISION – 2 TYPES
MITOSIS – makes….
 2 cells
 body (somatic) cells
 maintains the chromosome #
 diploid cells (2n)
 cells are genetically identical
 used for growth, maintenance
and repair
 Involves a cell cycle
MEIOSIS – makes…
 4 cells
 sex (germ) cells
 reduces the chromosome #
by ½
 haploid cells (n)
 cells are genetically different
 allows for the production of
new individuals
 DOES NOT involve a cell
cycle
PLOIDY IN CELLS
Ploidy refers to the number of complete sets of
chromosomes in a biological cell
DIPLOID CELLS (2n) contain 2 complete sets of
chromosomes – one set from each parent
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somatic (body) cells are diploid
HAPLOID CELLS (1n) contain only 1 set of chromosomes
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sex cells (sperm and egg) are haploid
POLYPLOID CELLS – contain more than 2 sets
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common in plants, fatal in animals
9.2 – MITOSIS AND CYTOKINESIS
Key activity of mitosis = accurate separation of the
cell’s replicated DNA
 Mitosis results in 2 “daughter” cells that are
GENETICALLY IDENTICAL
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WHY DO MULTICELLULAR ORGANISMS USE
MITOSIS?
 to increase the number of cells – growth
 to replace damaged cells – maintenance and repair
4 STAGES OF MITOSIS - PMAT
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Prophase
Metaphase
Anaphase
Telophase
When a cell is not dividing,
the DNA is present in
strands called
CHROMATIN
Before cell division, the…
DNA will replicate
(copy itself)
and begin to condense
(become more compact)
Eventually ,this will
form…double-stranded
CHROMOSOMES
(rod-like structures)
A DOUBLE-STRANDED CHROMOSOME
HAS….
2 identical parts called (sister) chromatids …..
held together by a centromere (protein disc)
PROPHASE
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chromatin tightens and forms (double stranded)
chromosomes – composed of 2 “sister” chromatids
spindle apparatus forms
nuclear membrane begins to break down and disappear
METAPHASE
 chromosomes
(sister
chromatids) are pulled
toward the center
(equator) of the cell
ANAPHASE
 Chromosomes
(sister chromatids) are pulled
apart and move toward the poles of the cell
TELOPHASE
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single stranded chromosomes arrive at the poles and begin to
relax into chromatin
nuclear membrane reforms (around 2 distinct nuclei)
2 identical sets of genetic material are in the cell
CYTOKINESIS
division of the cell and its contents into 2
“daughter” cells
Cytokinesis results in 2 cells…each
genetically identical
Cytokinesis differs in animal and plant cells
CYTOKINESIS IN ANIMAL CELLS
 the
cell membrane
pinches in and
separates the
dividing cell using a
cleavage furrow
CYTOKINESIS IN PLANT CELLS
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A cell plate forms along
the equator (of the cell)
and separates the cell
into 2 cells
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A new cell wall will form
on either side of the cell
PROCESS OVERVIEW
THIS MAY HELP…
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
I
P
M
A
T
C
- Interlude
- Prepare
- Meet
- Apart
-Tear
- Complete!
WHY IS MITOSIS NECESSARY?
3 reasons…..
Growth – adds new cells
 Repair – of damaged tissues and parts
 Maintenance – cells are always dying
and need to be replaced
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HOW IS MITOSIS
DIFFERENT AS WE AGE?
Mitosis occurs very quickly during the early stages of
life… just think we start out as one cell, a fertilized
egg (zygote) and within 10 months we weigh 6,7, or 8
pounds – whew
Mitosis continues to occur fairly rapidly as we grow,
however, in adulthood and into old age the process
slows.
LET’S PRACTICE..
NAME THE STAGES OF MITOSIS
NAME THE PHASES OF MITOSIS
PLANT OR ANIMAL CELLS?
MITOTIC PHASE?
PLANT OR ANIMAL CELLS?
MITOTIC PHASE?
LET’S PRACTICE…
PLANT OR ANIMAL CELLS?
MITOTIC PHASE?
ONE MORE TIME…
9.3 - CELL CYCLE REGULATION
NORMAL CELL CYCLE
 the TIMING and RATE of cell division is important
 The RATE OF DIVISION - depends on type of cell
CYCLINS & CDKs (proteins) – help regulate the cycle
 there are built in “check points” that monitor the cycle
and stop it if needed
ABNORMAL CELL CYCLES….
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Cancer
Apoptosis
Stem Cells
CANCER
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uncontrolled growth and division
of cells
cancer cells grow and divide
UNCONTROLLED
cancer is due to A FAILURE TO
REGULATE THE CELL CYCLE
carcinogens are -- CANCER
CAUSING AGENTS
UV radiation – THE MORE
RADIATION THE GREATER THE
RISK
the risk of cancer INCREASES
WITH AGE
CANCERS CAN FORM MASSES
OF CELLS CALLED TUMORS
Malignant Tumors
 invade and destroy nearby
tissues
 are life-threatening
 are severe and become
progressively worse
Benign Tumors
 do not invade other tissue
 are not life-threatening
APOPTOSIS
PROGRAMMED CELL DEATH – not every cell is
destined to survive
Cells going through apoptosis shrink and shrivel in a
controlled process
All animal cells appear to have a “death program” that
can be activated
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Helpful because ….it can help protect organisms from
developing cancerous growths
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2 examples:
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fingers and toes
leaves
STEM CELLS
Are unspecialized
(“blank”)cells – that
can develop into
specialized cell types
2 types:
Embryonic Stem Cells
 Adult Stem Cells
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WHAT IS SPECIAL ABOUT STEM CELLS?
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Have the ability to renew themselves and
develop into many different cell types
have potential medical uses in disease
treatment because they are not specialized
in structure and function
EMBRYONIC STEM CELLS
taken from an
embryo
 embryo = up to
week 8 of
development
 have greater
potential for
becoming various
cell types
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ADULT STEM CELLS
 taken
from the
tissues of a growing
human
 Found in bone
marrow - also
believed to be in
brain and heart
 may not be able to
differentiate into all
cell types