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Cell Reproduction
Chapter 10, 11-4
Cells Grow!
• Living organisms are made of cells. Like
living organism, cells also go through
periods of growth, and ultimately divide to
produce more cells.
• Cell growth is limited by:
– DNA overload
– Information/material exchange
Cell Division
• Chromosomes:
– Condensed chromatin
– During the cycle of a cell,
chromosomes appear as X during
mitosis.
– These X-shaped chromosomes
are made up of a pair of identical
chromosomes, each called a
Chromatid.
– The chromatid are attached at a
point called the Centromere.
• During the life of a cell it
follows a number of set
steps that occur. These
steps are called the Cell
Cycle.
Chromosomes
• Each organism has a set number of chromosomes in its
cells.
– Humans for example have 46 chromosomes
– Flies have 8
• There are 2 types of cells:
– Autosomal: Non-sex cells. The cells in the rest of the body.
– Gamete: Cells involved in sexual reproduction.
• Haploid vs. Diploid
– The total number of chromosomes in these 2 types of cells differ.
In autosomal cells 2 sets of chromosomes exist.
– In the sex cells (gametes) only 1 set of chromosomes exist.
Chromosomes
• In Humans:
• 23 unique
chromosomes
(Haploid number
= 23)
– In autosomal
cells: 46
chromosomes
total OR 2 pairs of
the 23 unique
chromosomes.
– In gametes 1 set
of the unique 23
chromosomes.
Cell Cycle
• 2 Major phases to
the Cell Cycle:
• Occurs in somatic
cells of organisms.
– Interphase: “inbetween” period
– Mitosis – period of
cell division
• The result of the
cell cycle are 2
identical cells
called daughter
cells.
Cell Cycle
• Mitosis and
Interphase have
subphases. In
these subphases
specific events
occur.
• Ultimately there
needs to be an
equal division of
the cell contents in
order to produce 2
healthy cells.
Mitosis
• Mitosis begins with one
adult cell.
• Through a series of
steps, this adult cell spits
into 2 identical daughter
cells.
Interphase
• Has 3
major
subphases.
• G1, S, and
G2
Interphase
• In G1 of
Interphase the cell
grows normally
and performs its
regular functions
• In the S phase the
DNA is replicated
(double the DNA)
• In G2 the cell
makes ready to
divide.
Mitosis
• Within the mitosis
phase, there are 4
major subphases.
• Each phase is
clearly visible and
has defining
features.
Prophase
• This is the longest of the
4 mitosis phases.
• In animal cells the
centrosomes form on
either side of the
chromosomes.
• Spindles (microtubules)
attach the chromosomes
to the centrosomes
• The chromatin
condenses to
chromosomes.
• The nuclear envelope
and nucleolus disappear.
Metaphase
• Most obvious of the
mitosis phases.
• Chromosomes line up
in the center of the cell
(called metaphase
plate).
• Each chromosome is
attached by spindle
fibers to both
centrosomes.
Anaphase
• The sister chromatids
are separated by the
pulling centromeres.
• The chromosomes
continue to move
until they reach
opposite polls of the
cell.
Telophase
• The daughter cells
begin to separate along
the metaphase plate.
• The chromosomes
disperse into
chromatin.
• Meanwhile, the nuclear
envelop begins to
reform. As does the
nucleolus.
• The spindle fibers start
to break apart.
Cytokinesis
• Occurs during Telophase!
• Animal Cells
– cell membrane pinches
inwards
• Plant Cells
– Cell plate is formed from
Golgi in cell membrane
– Cell wall forms between this
• Cell Plate Formation
Regulating the Cell Cycle
• Controls of Cell Cycle:
– Cells can only divide a
certain number of times.
– Cells stop dividing when
they come in contact
with other cells (Known
as Contact Inhibition).
Regulation of Cell Cycle
• Regulators of the Cell Cycle
• A group of proteins known as cyclins regulate
the timing of the events of the cell cycle.
– Internal Regulators: proteins within the cell that
respond to events, such as DNA replication,
alignment of chromosomes.
– External Regulators: proteins that respond to events
outside the cell. Signal the cell to speed or slow down
the cycle.
Cancer
• When cell cycle regulation
goes wrong, the result is
the formation of cancer.
• Cancer cells are those that
continuously divide, and
ignore Cell Cycle regulation
signals.
• Cancer is caused by
altering the regulators of
the cell cycle. Many
substances such as
tobacco smoking, virus
infections and radiation
have lead to disruption of
growth controlling proteins.
Cancer
• Cancer is caused by a number of
mutations within a cell. It is not a one hit
wonder!