Chapter 10:
Cell Growth and Division
Why do cells divide – why can’t they just grow
bigger?
• Surface area represents ability to take in/get
rid of materials.
• Volume represents needs of the cell – food,
oxygen, water, etc.
•Small cube 1 mm
tall
•Surface area = 6
mm2
•Volume = 1 mm3
•Surface area to
volume ratio = 6:1
•Larger cube 2 mm tall
•Surface area = 24
mm2
•Volume = 8 mm3
•Surface area to
volume ratio = 3:1
•As a cell grows, the volume of the inside
grows faster than the cell membrane
around the outside
•What happens when a cell gets too big?
•It could starve – can’t take in enough
food to support needs
•It could poison itself – can’t get rid of
waste fast enough
•So cells stay small for exchange of
materials
•Rather than grow bigger, cells divide and
increase in number
•Cell division occurs when:
•Body growth
•Maintenance and repair
•Fighting infection
•Replacing worn/dead cells
Chromosome Structure
•Chromatin – made of DNA and protein
•Seen in a non-dividing cell
•Chromosomes – Chromatin that has coiled
tightly
•Seen in a dividing cell
•Histones – proteins that help to coil the
DNA and maintain the shape of
chromosomes
•After replication, there are 2 identical
sister chromatids, held together by a
centromere
Eukaryotic Cell Cycle
• A repeating sequence of cellular growth
and division during the life of a cell.
http://www.cellsalive.com/cell_cycle.htm
• Most of the cell cycle is spent in interphase
(time between cell divisions):
• G1 stage – cell growth and activity
• S stage – DNA replication occurs (S
stands for synthesis of DNA)
• G2 stage – continues to grow and cell
prepares for cell division
•Amount of time spent in interphase
varies – average for adult mammals is 20
hours
•Nerve cells and muscle cells exit the cell
cycle  G0 phase
•Body never makes more of them
• Following interphase is the M stage,
including mitosis and cytokinesis
• Mitosis:
• 2 daughter cells are produced that are
identical to the parent
• Occurs in body cells
• Diploid cells produce other diploid cells
• Takes about 4 hours
http://www.cellsalive.com/mitosis.htm
http://www.copernicusproject.ucr.edu/ssi/HighSchoolBioResources/C
ell Division/Mitosis/Introduction_to_Mitosis.asf
Mitosis overview
1.
2.
3.
4.
5.
6.
7.
8.
Centriole
Chromatin
Nucleolus (in yellow)
Nuclear membrane
Spindle fibers
Chromosome (replicated)
Centromere
Sister Chromatids (each half of replicated
chromosomes)
9. Daughter Chromosomes (once the replicated
chromosome splits)
10.Cell membrane
11.Cell membrane pinches in
Early Prophase
•Chromatin coils to
become chromosomes
•Centrioles move to
opposite ends of the
cell
•Nuclear membrane
and nucleolus
disappear
Late Prophase
•Spindle fibers
form
•Chromosomes
become attached
to spindle fibers
– centromere
attaches to
spindle fibers
Metaphase
•Chromosomes
line up at
equator
(middle)
Anaphase
•Sister chromatids
separate, becoming
daughter
chromosomes, and
move toward
opposite ends of cell
Telophase
•Spindle fibers
disappear
•Nuclear membrane
and nucleolus
reappear
•Chromosomes uncoil
and turn back into
chromatin
• Cytokinesis, or division of cytoplasm,
accompanies mitosis.
• Division of the cytoplasm begins in
anaphase, but is not completed until end
of telophase.
• In animal cell, cell membrane is flexible
and pinches in to divide cell.
• In plant cells, rigid cell wall does not
bend, so a cell plate forms to divide the
cell.
Mitosis in Plant Cells
•Same phases as in animal cells
•No centrioles
•Cell plate forms instead of cell membrane
pinching in
Cytokinesis in animal cells
http://www.copernicusproject.ucr.edu/ssi/HighSchoolBioResources
/Cell Division/Mitosis/Mitosis_Video_Quiz.asf
Cytokinesis in plant cells
•
•
•
•
Cell Division in Prokaryotes
The process of asexual reproduction in
prokaryotes is called binary fission.
The two daughter cells are identical to the
original parent cell, each with a single
chromosome.
Following DNA replication, the two
resulting chromosomes separate as the
cell elongates.
Cell divides without cell structures seen
in plants & animals
http://www.microbelibrary.org/images/MondoMedia/2bhirez.mov