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Cell Division
Binary Fission
 Prokaryotic Cells
 Asexual Reproduction
 When a bacterium has grown so that it has
doubled in size, it replicates its DNA and divides
in half, producing two identical “daughter cells”
http://www.britannica.com/EBchecked/topic/65525/binary-fission
Cell Division - Part I
Reproduction is necessary for
the continued survival of all
living things.
In order to grow and
reproduce, cells must divide!
Cell Division – Part I
 The process by which two cells are formed from one.
 There are two types of cell division: mitosis and
meiosis.
 Most of the time when people refer to cell division,
they mean mitosis, the process of making new body
cells.
 Meiosis is the type of cell division that creates egg
and sperm cells.
Cell Division – Part I
 First Stage: Mitosis - Division of the cell nucleus
 Second Stage: Cytokinesis - Division of the
cytoplasm
Let’s consider mitosis first:
 Mitosis is a fundamental process for life.
 A cell duplicates all of its contents, including its
chromosomes, and splits to form two identical
daughter cells. Each of which begins the cycle
again.
Cell Division - Mitosis
There are 4 phases of mitosis:

Prophase

Metaphase

Anaphase

Telophase
Prophase
Centrioles
Spindles forming
•The first phase and longest of mitosis; occurs when chromatin condenses
becoming chromosomes and the mitotic spindle begins to form.
•Spindles; fanlike microtuble structures which help to separate
chromosomes.
•The centrioles separate to opposite sides of the nucleus organizing
spindles
•Chromosomes (Paired identical “sister” chromatids)
http://www.biologycorner.com/bio1/cellcycle.html
•The nuclear envelope begins to break down
(dashed line)
Metaphase
Centrioles
•Typically happens very quickly
•Chromosomes line up along the equator.
(Note: This is a signature feature of metaphase.)
•Each chromosome is connected along the poles of the spindle
fiber at its centromere
http://www.biologycorner.com/bio1/cellcycle.html
Anaphase
Individual chromosomes
•The “sister” chromatids separate into individual chromosomes
and move apart to opposite poles
(Note: These are signature features of anaphase.)
•Phase ends when chromosomes stop moving
Telophase
Nuclear Envelope Reforming
•Fourth and final phase (not stage) of mitosis
•Chromosomes begin to disperse into a tangle of dense material.
•Nuclear membrane (envelope) forms around each group of
chromosomes
•The spindle begins to break apart, and a nucleolus becomes visible in
each daughter nucleus.
virtual.yosemite.cc.ca.us
•Cytokinesis begins
Cytokinesis
• The process by which the cytoplasm divides (pinches)
and one cell becomes two individual cells.
•Each daughter cell has an identical set of duplicate
chromosomes.
• Note: The process is different in plants and animals
Animals - Cell
pinches inward
(cleavage
formation by
furrow),
Nuclear
Membrane
starts appearing
with thread-like
structures
Plants - a new
cell wall forms
between the
two new cells.
Nuclear
membrane
starts
appearing with
thread-like
structures
Time-Lapse Video of Mitosis
Another time-lapse video, see if you can pick out the stages of mitosis:
Cell Division - Mitosis
 To summarize mitosis, you
start with one parent cell
containing diploid (2N)
chromosomes.
 After one round of mitotic
division, you end up with 2
daughter cells that are
identical to the original parent
cell
 That is, each daughter cell
contains the same number of
chromosomes as the parent
(2N)!
THE CELL CYCLE
• If you were going to divide the cell cycle into two
parts:
1. Interphase
2. Cell Division
•
The life of a cell is one division after another
separated by an “in-between” period of growth
called interphase.
•
The cell cycle is the series of events that cells go
through as they grow and divide.
THE CELL CYCLE
• During the cycle a cell grows, prepares for division,
and divides to form two daughter cells, each of which
then begins the cycle again.
•
The Cell Cycle consists of four phases:
1. Mitosis and Cytokinesis (Cell Division) (M Phase)
Note: Interphase makes up other three phases
2. Chromosome replication (or synthesis) (S Phase)
3. Cell Growth (G1 Phase)
4. Preparation for mitosis (G2 Phase)