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Cell Growth and
Division
Chapter 10
Why are cells so small?

DNA
– Messages from the nucleus must be
able to reach all parts of the cell

Diffusion
– Nutrients must enter and wastes
must leave
– If the cell was too big, diffusion
would happen too slowly
Why are cells so small?
 Surface
Area vs. Volume
–As a cell grows larger, the
volume increases faster than the
SA
–A bigger cell needs more
nutrients, but has relatively less
SA to take in those nutrients
Surface Area vs. Volume
Cell Size
5 cm
10 cm
Surface
Area
(l×w×6)
Volume
(l×w×h)
SA to
Volume
Ratio
150 cm2
600 cm2
125 cm3
1000 cm3
150/125 = 600/1000
6:5
= 6:10
Cell Cycle



Cells divide before growing too large
Before dividing, cells must prepare
Preparation = Interphase
– G1 phase: Cell grows larger
– S phase: Cell makes new DNA for
daughter cell
– G2 phase: Cell makes new organelles for
daughter cell
Cell Cycle
Chromosomes


Each chromosome is
replicated during the S
phase
A replicated
chromosome has two
identical sister
chromatids connected
by a centromere
Centromere
Sister Chromatids
Mitosis
Mitosis

Four Stages:
– Prophase (pro- means first)
– Metaphase (meta- means middle/after)
– Anaphase (ana- means apart)
– Telophase (telo- means far away/end)
Prophase




Chromatin condenses
into chromosomes
Nuclear envelope and
nucleolus disintegrate
Centrioles migrate to
opposite ends of the cell
Spindle fibers form in
foot ball shape across
cell
Chromosomes
condensing
Prophase
Metaphase


Chromosomes
line up in the
middle (equator)
of the cell
Spindle fibers
attach to
centromeres
Anaphase




Sister chromatids
separate
Spindle fibers shorten,
pulling chromatids to
opposite ends of cell
Animal cells begin to
pinch in
Plant cells begin to form
cell plate in the middle
Anaphase
Telophase



Nuclear membrane
built from ER around
each set of
chromosomes
Nucleolus reforms in
each nucleus
Chromosomes
become mass of
chromatin
Telophase
Two cells dividing into
four
Cytokinesis



Final division of cytoplasm resulting in
two daughter cells
Animals – CM pinches together
Plants – Cell plate forms new CM
dividing the daughter cells
Plant Cell Division
Which phases can you see?
Anaphase
Metaphase
Telophase
Prophase
Interphase
Knowing when to divide

Cyclins
– Protein that regulates the cell cycle in
eukaryotes


Internal regulators – tell the cell when
to enter mitosis
External regulators – control the rate
of the cell cycle
Cellular Response to Injury
Effect of Cyclins
Cytoplasm is
removed from
cell in mitosis
Cytoplasm is injected
into a second cell in G2 phase
Second cell enters mitosis
Cancer



Cancer results when cells do not
respond to cell cycle regulators
Cells grow unregulated, forming a
tumor
Tumor damages surrounding tissue
Leukemia – Blood cancer
Mammary (Breast) Cancer
Skin Cancer