Biology Chapter 10:
Cell Growth and Division
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Let's start from the beginning...
• A long time ago our
ancestors noticed
that some things
tended to reproduce
themselves - traits
were inherited.
Unfortunately, that's
not always a good
thing!
What is a chromosome?
• Threadlike structure in nucleus >
contains genetic information - passed on
from one generation of cells to the
next
– Genetic information = DNA (“blueprints”
of life)
– DNA in form of a code (genes) > dictates
everything from eye color to how long you
live
– “It’s in your genes” should actually be “It’s
in your DNA
Gene
• Sequence of DNA that codes for a
protein and determines a trait
– Trait = specific characteristic that varies from
one individual to another
– Ex: height, hair and eye color
• Genes are the bands on chromosomes.
– The thicker the band, the more information it
holds.
Living things grow by producing
cells.
bacteria (0.5 to 1.5 microns)
red blood cell (5 microns)
lymphocyte (5 to 8 microns)
As a cell grows larger, it…
• Places more demands on its DNA
– DNA “Overload”
– Compare to town library (town grows, more
demand for books)
• Has more trouble moving enough
nutrients and wastes across its membrane
(in and out of cell)
The cell will eventually divide into two
daughter cells.
Cell Division
• Process by which a cell
divides into two daughter
cells
– DNA replicated before division
– Each daughter cell gets one
complete set of genetic
information
• Two stages:
– Mitosis - nucleus divides to
form two identical nuclei
– Cytokinesis - cytoplasm divides
to form two identical cells
Chromosomes
• Made up of DNA (genetic information) and
proteins > chromatin
• Each chromosome has two identical “sister”
chromatids - one goes to each new cell
• Cells of every organism have specific
number of chromosomes
– Ex: fruit flies 8, carrots 18, humans 46
• Duplicated chromosomes are called dyads
• Duplicates held together by centromere
• Homologous pair = 1 of each pair
acquired from one of the parents
The Cell Cycle
• Cell grows, replicates its DNA, and
divides into two daughter cells
• Four phases
~ M phase > Mitosis and cytokinesis
(cell division)
~ S phase > Synthesis (chromosome
replication)
~ G1 and G2 > “Gap” phases (periods of
intense Growth and activity)
Interphase
• Period of cell cycle between cell
divisions
• All phases except M
– Made up of G1, S, and G2 phases
– Split because M phase occurs much more
quickly
• Includes: DNA replication, protein
synthesis, and synthesis of organelles
and materials needed for cell division
• Mitosis > Process in which the
nucleus divides to form two
identical nuclei
Four Phases of Mitosis
• Prophase
• Metaphase
• Anaphase
• Telophase
Prophase
• Chromatin condenses
into chromosomes
• Nucleolus disappears
• Centrioles separate
– Two tiny “anchors” in
cytoplasm near nuclear
envelope
• Fanlike fibers extend to
form spindle
Pair of
Centrioles
Chromosome
(two sister
chromatids)
Centromere
Metaphase
• Chromosomes line up along center of
cell
– Each chromosome connected to spindle
at centromere
(Imaginary line)
Anaphase
• Sister chromatids separate and
move to opposite sides of cell
Telophase
• Chromosomes gather at opposite
ends of cell
• Two new nuclear envelopes form
Chromosomes
gathering
New nuclear
envelopes
forming
Cytokinesis
• Cytoplasm pinches in half
• Each daughter cell has identical set of
duplicate chromosomes
New individual cell
Uncontrolled Cell Growth
• Cancer
– Disorder in which some
cells lose ability to control
growth
– Cells do not respond to
signals that regulate
growth of most cells
– Result > divide
uncontrollably and form
masses of cells called
tumors
Results of Mitosis
• Mitosis is the division of a NUCLEUS
• Mitosis produces two new nuclei with the
SAME number of chromosomes as
original nucleus
• Mitosis is ASEXUAL
– ONE parent = 2 IDENTICAL daughters