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Cell Division
•
Life Cycle of the Cell
• Mitosis
• Meiosis
Cellular Division
Cell division is a
process by which a
cell, called the
parent cell, divides
into two or more
cells, called
daughter cells. Cell
division is usually a
small segment of a
larger cell cycle.
3 major types of cell division
Cellular Division
The size of the cell signals time for division.
Cell Grows
until it
reaches a
size large
enough to
start division.
Prokaryotic Division

Ex. Bacteria
 Prokaryotic Division is called Binary
fission, it is the division of a prokaryotic
cell into 2 daughter cells
 Consists of 3 stages:
1.
2.
3.
The 1 chromosome in the cell makes a copy of
itself (in a process that is similar to unzipping
and then reforming each side)
Cell grows until it reaches twice its original size
A cell wall forms between the 2 chromosomes
and the cell splits into 2 new cells
Identical to Original cell
Eukaryotic Division

More complex than prokaryotic cells
because of organelles (ex. Mitochondria,
endoplasmic reticulum, golgi bodies, chloroplasts, etc.)

The life of the eukaryotic cell is
diagrammed as the cell cycle – the
repeating sequence of growth and division
of eukaryotic cells (4 major phases)
Cell Life Cycle
G1,S, & G2
all make up
Interphase
Therefore, the
cell is usually
in interphase
Organelles
are copied
here
Cytokinesis
happens here
Cell Cycle
Animated
Mitosis – is the process that results in two
nuclei with the exact same information
• Interphase – pre-mitotic phase
PMAT:
• Prophase – 1st phase
• Metaphase – 2nd phase
• Anaphase – 3rd phase
• Telophase – 4th phase
• Cytokinesis – cell divides
•
•
•
Chromosomes are copied (# doubles)
Chromosomes appear as threadlike coils
(chromatin) at the start, but each chromosome
and its copy(sister chromosome) change to sister
chromatids at end of this phase
Longest phase of the cell cycle – G1, S, & G2
Nucleus
chromatin
CELL
MEMBRANE
Cytoplasm
Chromosomes
A chromosome is an
organized structure
of DNA and protein
that is found in
cells. It is a single
piece of coiled DNA
containing many
genes
Chromosomes
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
•
•
•
•
Mitosis begins (cell begins to divide) – nucleus
breaks down and nucleolus disappears
Centrioles (or poles) appear and begin to
move to opposite end of the cell.
Spindle fibers form between the poles.
Chromosomes condense & become visible
Centrioles
Sister chromatids
Spindle fibers
Animal Cell
Plant Cell
There are no centrioles in
plant cells they can divide
without them
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
•
Chromatids (or pairs of chromosomes) attach
to the spindle fibers. Chromatids line up at the
equator (center of the cell)
Centrioles
Spindle fibers
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
•
Chromatids (or pairs of chromosomes)
separate at the centromere and begin to move
to opposite ends of the cell.
Centrioles
Spindle fibers
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
•
•
•
•
Spindle fibers disappear
Two new nuclei form. Nucleolus returns to
the inside of each nucleus
Chromosomes uncoil and appear as chromatin
(threads rather than rods).
Mitosis ends.
Nuclei
Chromatin
Nuclei
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
•
Cell membrane or cell plate moves inward to
create two daughter cells – each with its own
nucleus with identical chromosomes.
- animal cells → cleavage (pinching) furrow forms
in the cell membrane to separate the cell.
- plant cells → cell wall forms to separate cell.
Animal Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Plant Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Cell wall
plate
http://www.cellsalive.com/mitosis.htm
Meiosis
Meiosis

Meiosis – the process that divides the # of
chromosomes in cells in half



2 successive nuclear divisions (goes through
PMAT twice)
Before 1st division, DNA is copied just like in
mitosis
However, DNA is not copied before 2nd
division
Meiosis




Broken down into 2
Diploid
parts – Meiosis I and
Meiosis II
DNA
Meiosis I – homologous
Copied
chromosomes separate
Meiosis I
into 2 diploid cells
Meiosis II – Each Cell Diploid
Meiosis II
Sister chromatids
separate into 2 haploid
Haploid
cells
1 Diploid Cell = 4 Haploid Cells
Difference between Animals & Plants

In Animals – meiosis
makes gametes
(reproductive cells /
sex cells – sperm &
eggs)

In Plants – meiosis
makes spores
2 Unique Events of Meiosis:
1.
Crossing Over:


2.
Homologous chromosomes
pair up next to each other
Arms of chromosomes
exchange segments (same
sized) of DNA
Skipping Replication:

Only 1 replication of DNA,
but 2 divisions → meiosis
halves the number of
chromosomes
Meiosis I
Prophase I:
a.
Chromosomes condense (become thick) and
become visible
b.
Nuclear envelope breaks down
c.
Homologous chromosomes pair up
d.
Crossing over occurs
2. Metaphase I:
a.
Pairs of homologous chromosomes move to the
equator (center) of the cell
3. Anaphase I:
a.
Homologues separate
b.
Chromosomes of each pair pull apart and move to
the poles (opposite ends) of cell
1.
Meiosis I
4.
Telophase I:
a.
Chromosomes gather at each of the 2 poles
b.
Cytoplasm divide, forming 2 new cells.
c.
Each cell produced now contains half the number of
chromosomes as the original cell
d.
Meiosis I often called reduction division
Skipping Replication – DNA does not copy
between meiosis I and meiosis II
Meiosis II
Is just like meiosis I except :
•
•
we calls stages Prophase II, Metaphase II, Anaphase II, and
Telophase II
4 new haploid cells are created instead of 2 diploid cells
Genetic Recombination



The formation of new combinations of
genes
2 chromatids of chromosomes no longer
contain identical genetic material
Provides a source for genetic variation,
which impacts the rate of evolution in
organisms
Mitosis vs Meiosis
1.
2.
3.
Mitosis
PMAT Once
Ends with 2 diploid cells
that are identical to
parent cell
Somatic Cells (Body
cells) undergo this
cellular reproduction
1.
2.
3.
Meiosis
PMAT Twice
Ends with 4 haploid cells
that are different from
the parent
Gametes (Sex cells)
undergo this cellular
reproduction
Mitosis vs Meiosis