All About Cell
Division
• Mitosis Presentation
• Observe Onion
Mitosis
• Mitosis Paper Plate
Activity
Mitosis
• Cells are constantly
being replaced or
making new cells
• Why do cell divide
instead of just
continuing to grow
larger?
Cell Growth??
• There are two main reasons why cells
divide instead of growing larger.
1. The larger a cell becomes, the more demands
the cell places on its DNA.
Cell Growth??
2. The cell has more trouble moving enough
nutrients and waste across the membrane
– The rate at which food, oxygen and water enter
a cell through its cell membrane. Waste
products leave in the same way. The rate of
which this exchange takes place depends on the
surface area of the cell.
– The rate at which food, oxygen and water are
consumed and waste products are produced
depends on the cell’s volume.
Ratio of Surface Area to Volume
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•
•
•
Ratio of surface area to volume = SA/V
Surface Area= 1cm x 1cm x 6= 6cm2
Volume= 1cm x 1cm x 1cm = 1 cm3
The Ratio of surface area to volume is this
example would be 6:1
Ratio of Surface Area to Volume
• Look at chart on pg 243
• Notice…the large the cell… (surface area and
volume)…
• Note that the volume increases much more rapidly
than the surface area, causing the ratio of surface
area to volume to decrease.
• This decrease creates serious problems for the cell
• So in order to avoid this…the cell will divide!
Mitosis
• As microscopes
evolved, this enabled
scientists to study the
stages of reproduction
of a cells’ life
Chromosomes:
• Carry genetic material
which is copied and
passed from
generation to
generation
• Always present in
cells but are usually
too small to see with a
microscope
• Reside within a welldefined nucleus
Chromosomes:
• Chromosomes
carry DNA.
• Most all
chromosomes
cannot be seen in
the cell EXCEPT
prior to division
and throughout.
CHROMOSMES
• Chromosomes will
appear as
Chromatin most of
a cells life.
• Long strands of
protein and DNA.
The Cell Cycle:
".
• Is the sequence of growth
and division of a cell
• A cell goes through 3
stages/periods
• 1. Interphase: Growth
period. (G1, S, and G2)
• 2. Mitosis: Division period
• 3. Cytokinesis- the actual
dividing of the membrane.
Interphase:
•
•
•
•
•
•
Most of a cell’s life is spent in Interphase
Here a cell grows and carries on daily activities
Divided into 3 phases
1) G1
2) S
3) G2
G1 Phase of Interphase:
• G1 phase: G stands for
growth.
• The period prior to the
replication of DNA.
• In this phase, the cell
begins its preparation for
division.
• The number of organelles
and cytoplasm will
increase.
S Phase of Interphase:
• S phase: The period
during which DNA
is replicated (or
copied).
• In most cells, this is
a narrow window of
time. Note the S
represents synthesis.
• Cell copies its
chromosomes and
DNA is doubled.
Replication:
•Remember if the Chromosomes
are duplicated it is safe to say that
the DNA is also replicated!!
•You have two identical
copies of your
Chromosomes/DNA inside
your cell at this point.
•We will talk in more detail
about DNA replication in
the Ch 11
You don’t have to copy anything
here…similar to your notes!
G2 Phase of Interphase:
• G2 phase:
• The period after DNA
replication has occurred but
prior to the start of prophase.
• The cell synthesizes proteins
and continues to increase in
size.
• The cell is making any
substance and organelles need
for division.
Mitosis:
• Mitosis is the process by which a cell ensures each
daughter cell will have a complete set of
chromosomes.
• There are four key stages of mitosis: (PMAT)
• Prophase, Metaphase, Anaphase, and Telophase
Prophase:
• DNA condenses into movable packages called chromosomes.
They become thicker and more visible.
• Remember…..Sister chromatins and the DNA they contain are
exact copies of each other.
• Nucleolus and nuclear envelope disappear.
• Spindle fibers and centrioles begin to assemble.
Metaphase:
• Chromosomes will begin to aligning at the cell’s
equator.
• The chromosomes are moved to the center of the cell
by the spindle fibers attached to the centromeres.
• The spindle is highly visible.
Anaphase:
• The centromeres of each chromosome are pulled by
the spindle fibers toward the ends of the cell
• The sister chromatids are thus separated from each
other
• They are now in their most tightly condensed form
Telophase:
• Final stage of Mitosis
• New nuclear envelope
and nucleolus begin to
appear
• Two complete sets of
chromosomes
• The chromosomes
begin to uncoil and
become invisible
Review of Mitosis:
Cytokinesis:
• Now there are two separate nuclei,
but they are in the same cell. The cell
needs to be split in half.
• The cytoplasma of the
cell divides into 2 new
cells called daughter
cells
• Exact copies of each
other
• Daughter cell nuclei are
identical to the parent in
every way
• All of your cells come
from ONE fertilized egg
Cytokinesis Differences:
• Plant Cell
• Cell plate will begin
to form separating the
2 cells.
• Animal Cell
• The cytoplasma will
pinch into 2 separate
cells.
• A cleavage furrow
begins to form.
Onion Root Mitosis
• Interphase, Prophase, Metaphase, Anaphase, and
Telophase
Regulating the Cell Cycle
• It’s very amazing how our human body works.
Not all cells in the body move through the cell
cycle at the same time or speed.
• For example human muscle cells and nerve cell
rarely divide at all once they have developed…this
is in great contrast with skin, digestive tract, bone
marrow cell which are continuously grow and
divide throughout their life.
Regulating the Cell Cycle
• Scientist have been
studying and observing
cell behavior for years.
• They soon discovered a
family of closely related
proteins that regulate the
timing of the cell cycle in
eukaryotic cells.
• They called these proteins
cyclin.
• They have been divided
into two types of
regulatory proteins: those
that occur inside the cell
(Internal Regulators) and
those that occur outside
the cell. (External
Regulators)
What if?
• What if the cyclin or the regulators are not
working properly?
• Uncontrolled cell growth?
• What is this called?
CANCER
• Benign- Non• Cancer is
spreading
abnormal cell
• Malignantgrowth.
Called tumors. Spreading
Usually
uncontrollable
ASEXUAL REPRODUCTION
• This is reproduction in which one
parent produces offspring by cell
division.
• This is common in plants though
their leaves, buds, steams or
flowers
• Seen less common in animals.
BUDDING
• Seen in Animals
• A new organism will
grow from a piece of
another.
• Ex: jellyfish, corals
and in some
parasitic animals
(tapeworms)
FRAGMENTATION
• Also seen in
Animals
• Separated pieces
of the parent
organism
develop into a
new organism.
•
• As certain tiny
worms grow to full
size, they
spontaneously break
up into 8 or 9 pieces.
Each of these
fragments develops
into a mature worm,
and the process is
repeated.
Parthenogenesis
• Parthenogenesis
• In parthenogenesis
("virgin birth"), the
females produce eggs,
but these develop into
young without ever
being fertilized.
• Parthenogenesis
occurs in some fish,
several kinds of
insects, and a few
species of frogs and
lizards.
Regeneration
• The growing
back of a
lost body
part through
mitosis.
COLORING ASSIGNMENT
• Draw, color, and label the following….Get 2
sheets of plain white/yellow paper
• First side of first sheet, pg 245….Pie Chart!! 2nd
side of first sheet….Pg 244 Chromosome…draw
and label the animated version. This needs to be
large and take up most of the side of paper.
• 2nd piece of paper draw the animated version of
Interphase-Cytokinesis. (I-PMAT-C) It must be
in the correct order!!!! Page 246-247..