Transcript Mitosis PPT - Effingham County Schools

The Great Divide
“MITOSIS IN A NUTSHELL”
To Be Answered…
THINK:
 How many cells are you composed of?
 When an organism grows bigger do you
get more cells or just bigger cells or both?
 When do your cells divide the fastest?
Slowest?
 Do cells ever stop dividing?
 Are all cells capable of division and
replacement?
WHY DO CELLS DIVIDE?
•To keep a workable ratio of
surface area to volume
V=lxwxh
SA = l x w x 6
1 cm
2cm
V = 1 cm3
V = 8 cm3
SA = 6 cm2
SA = 24 cm2
Ratio = 6/1
Ratio = 24/8
6:1
3:1
-As cell gets larger, ratio decreases
3 cm
V = 27 cm3
SA = 54 cm2
Ratio = 96/64
2:1
Why Would a Cell Divide?
 As cells absorb nutrients and get larger, the
volume of the cell increases faster than the
surface area
Surface area
for exchange
not great
enough to
support cell’s
needs
 This means that a cell can no longer absorb
nutrients and get rid of wastes fast enough to
support its demands (volume) = STARVE TO DEATH
 So what’s a cell to do?
 Solution: divide in 2!
When Would a Cell Divide?
 Growth
 Repair or Replacement
 Cancer
Different cells divide at different rates:
 Most mammalian cells = 12-24 hours
 Some bacterial cells = 20-30 minutes
Getting Older…
 All cells are only allowed to complete a
certain number of divisions
 Then they die (programmed cell death)
How does cell division change over a lifetime?
 Childhood = cell division > cell death
 Adulthood = cell division = cell death
 The Later Years = cell division < cell death
The Cell Cycle
INTERPHASE
Stages of the Cell Cycle
 2 stages = interphase (growth & replication of
DNA) & mitotic phase (division of cell into 2
daughter cells)
 Cell spends
about 90% of
the time in
interphase
Interphase
 Divided into 3 phases:
 G1 = Growth Phase – Cells grow and develop,
undergo protein synthesis and rapid growth
 S = Synthesis Phase - DNA replication occurs
(i.e. chromosomes copied) in preparation for
making new cells during mitosis
 G2 =Second Growth Phase = centrioles
replicate, cell prepares for cell division, makes
new cell parts
 Becomes too large = divide in 2
The Mitotic Phase
 Equal distribution of 2 sets of chromosomes (DNA)
into 2 identical daughter cells
 Divided into 4 stages of Mitosis:
 Prophase
 Metaphase
 Anaphase
 Telophase
 Cytokinesis
Cell Cycle Tidbits
How long is one cell cycle?
 Depends on the cell- skin cells = ~24
hours, nerve cells = never after
maturity, cancer cells = very short
 Remember: every cell only has a
certain # of divisions it can undergo,
then it dies = (programmed cell death)
Mitosis: A Closer Look
 Prior to entering the mitotic
phase, the cell has just come
out of Interphase
Interphase
 Replicated DNA during S
(synthesis)
 2 complete set of
chromosomes that must
be distributed equally
between 2 cells = mitosis
 Chromatin condenses
visible chromosomes
 Appear as sister
chromatids held
together by centromere
 Nuclear membrane
dissolves
 The centrioles migrate to
opposite poles & spindle
fibers form between
them
Prophase
Duplicated Chromosome
Mitotic Appearance (Prophase)





Centriole
Centromere
Spindle
Chromosome
(chromatids)
Aster
Metaphase
 Chromosomes
line-up on the
metaphase
plate
 Centromeres
are attached to
spindle fiber
Anaphase
 Centromeres divide
 Spindle fibers
contract
 Result = sister
chromatids are
pulled away from
one another
towards the poles
Telophase
 The chromosomes
reach the poles
 Nuclear
membranes form
around the 2 new
nuclei
 The cytoplam
distrubted equally
between the 2
new cells
 In animals, the
cell membrane
pinches together
 In plants, a cell
plate forms from
inside out
Cytokinesis
Animal
Plant
Cytokinesis in plants
A cell plate made up of cell-wall
components gradually forms in the middle
of the cell.
Cytokinesis in animals
Cleavage
Furrow
A cleavage (or division) of the animal cell.
The membrane pinches together forming 2
cells
ANIMAL VS. PLANT MITOSIS
 ANIMAL CELL
Centriole and
aster present
 Daughter cells
separated by
cleavage
furrow

 PLANT
CELL
 No visible
centriole or
aster
 Daughter cells
separated by
cell plate
What Mitosis Actually Looks Like
Interphase
Prophase
Anaphase
Metaphase
Telophase
Figure 9.8
– Part 2
Figure 9.8 – Part 2
Mitosis consists of several different phases.
Summary of Mitosis
What Happens After Mitosis?
 The cell
returns to
interphase
 Chromosomes
uncoil back
into chromatin
 The cycle
repeats itself
over & over…
At What Stage Are Our Cells At In The Cell Cycle?
 Different cells can
be in different
stages
 Interphase
 Mitosis:
 Prophase
 Metaphase
 Anaphase
 Telophase
 Cytokinesis
Can You Identify the Stages of Mitosis?
Put the
following
mitosis
stages in the
correct
sequence
Mitosis
Can you name
the stages?
A
B
C
D
E
The Guarantee
 The product of
mitosis is 2 cells
 The daughter cells
are identical to
each other & to the
mother cell
Why is this so
important?
Mother
cell
Identical
daughter
cells
The Daughter Cells
 In humans, the 2
daughter cells will have
46 chromosomes (23
pairs)
Mother
cell
 1 chromosome
originally from mom & 1
from dad
 Each chromosome is
said to have the same
gene sequence
Identical
daughter
cells