What do you want to be
when you grow up???
Cell Differentiation
• Zygotes (sperm + egg) first divide into
embryonic stem cells.
• Stem cells develop in two stages.
– Determination-cells commit to become one
cell type
– Differentiation-cells acquire specialized
structures and functions of highly specialized
cells
• Specific genes are turned on and off
Quick Question…
• How does the process of
cell determination differ from
the process of cell
differentiation?
Cell Cycle
&
Mitosis
Chapter 5
Hmm…
• Why do you have to keep cutting your
fingernails….grass……hair??
Cell cycle has 3 main phases
Cell Cycle
INTERPHASE
G1 phase
The cell grows
S phase
G2 phase
The DNA replicates
The cell prepares to
divide
Parts of the Cell Cycle
•
•
•
•
A.
Interphase – Growth period of the
cell. Consists of 3 phases:
1. G1 = Rapid growth and
metabolic activity (production
of organelles)
2. S = DNA synthesis
(replication)
3. G2 = Growth and protein
synthesis (centrioles
replicate)
G1 or gap 1
• phase in which daughter cells are growing
and carrying out their normal functions
(example: skeletal muscle cells-contract
and joints move)
• the cells are 2n and 2c (they are diploid
and have 2 copies of each of the
chromosomes)
S phase or synthesis
• DNA replication occurs, making duplicate
copies of each of the chromosomes in
preparation for cell division (each
chromosome consists of 2 sister
chromatids which are tightly bound to each
other)
• the cells are 2n and 4c (they are diploid,
but have 4 copies of each chromosome)
A Chromosome
Chromosome
• Chromosome-one
long continuous
thread of DNA that
consists of
numerous genes
along with
regulatory
information
G2 or gap 2
• the cells may grow more at this point
• at the end of G2, chromosomes begin to
condense in preparation for cell division
Interphase
Interphase
• the "holding" stage or
the stage between
two successive cell
divisions.
• Some 90% of a cell's
time in the normal
cellular cycle may be
spent in this phase
C= chromatin
I = nucleolus
Mitosis
M Phase
Prophase
Metaphase
Anaphase
Telophase
2 processes involved in Division
– Mitosis-division of cell nucleus and its
contents
– Cytokinesis-process that divides the cell
cytoplasm
– Result of mitosis is two daughter cells that are
genetically identical to the original
Cells divide at different rates
• Prokaryotes typically divide faster because
they do not have membrane bound
organelles and cytoskeleton
Prophase
The nuclear membrane breaks down and the
chromosomes become short and thick.
By late prophase, individual chromosomes are visible,
appearing as two parallel threads attached at a
constriction point called the centromere.
Prophase
• the chromatin
condenses into
discrete
chromosomes.
• The nuclear
envelope breaks
down and spindles
begin to move to the
opposite "poles" of
the cell.
Prophase
Metaphase
The spindle fibers attach to each chromosome on
either side of its centromere. The spindle fibers
force the chromosomes into a tight plane which
is a circle around the middle of the cell
Metaphase
• the nuclear membrane
disappears completely.
• The spindle fully develops
and the chromosomes
align at the metaphase
plate (a plane that is
equally distant from the
two spindle poles).
Ch= chromosome
S= spindle
Metaphase
Anaphase
• Anaphase is the shortest stage of mitosis and is the
separation of the chromosomes. The chromatids that
were attached to the same centromere now separate
and move to opposite poles of the spindle. The
chromosome arms from a “V” as they are dragged
through the cytoplasm. By the end of anaphase,
chromosomes have been separated into two genetically
identical nuclei.
Anaphase
• the paired
chromosomes (sister
chromatids) separate.
Spindle fibers
attached to the sister
chromatids shorten
and begin moving
them to opposite ends
(poles)
Anaphase
Early Telophase
• nuclei begin to form at
opposite poles.
Cytokinesis, the
division of the original
cell's cytoplasm, also
begins.
• In plants, the cell
begins to form a cell
wall.
Late Telophase
• the chromosomes are
cordoned off in
distinct new nuclei in
the emerging
daughter cells.
• The division of the
original cell's
cytoplasm is called
cytokinesis
Telophase
Telophase is prophase in reverse. The spindle
fibers disappear, a nuclear membrane forms
around each of the two sets of chromosomes,
and a nucleoli appears in each new nucleus.
The chromosomes become longer.
Telophase
Cytokinesis
Cytokinesis splits the cytoplasm of dividing cell into
daughter cells.
Cytokinesis
Can you identify?
Can you identify?
What phase?
What phase?
Name that phase!
Name that phase!
Onion Root Tip
Onion Root tip