Download Chapter 8: Cell division: Mitosis

The Cellular Basis of Reproduction
and Inheritance
PowerPoint Lectures for
Campbell1408
Biology: Concepts & Connections, Seventh Edition
Biology
Reece, Taylor, Simon, and Dickey
Dr. Chris Doumen
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
Introduction
!  In a healthy body, cell division allows for
–  growth,
–  the replacement of damaged cells, and
–  development from an embryo into an adult.
–  These cell division occur by means of a process of
mitosis
!  In addition, sexually reproducing organisms require
eggs and sperm cells
–  These are made by a cell division process called
meiosis.
© 2012 Pearson Education, Inc.
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Introduction
!  The human body
contains about 50
trillion cells. And
they all function
perfectly. How do
you get 50 trillion
from one fertilized
cell ?
! Also, the body is continuously replacing worn out
cells. Every day, million of cells need to be replaced.
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Introduction
!  For example : Every second, about
2 million new red blood cells are
destroyed and 2 million new ones
are made in a healthy human
individuals.
!  Bone tissue is remodeled
constantly and old bone material is
replaced with new. Estimates are
that 10 % of your bone mass is
remodeled every year.
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!  This requires an enormous
productive cell division (aka
mitosis)
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Introduction
!  A seastar can regenerate a lost
arm by means of cell division and
growth ( also by mitosis)
!  Humans can regenerate
certain tissues, but major
regrowth of structures
(such as a limb) is not
programmed into our repair
mechanism (yet).
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Introduction
!  On the other hand, what happens when
cells divide out of control ? We call this
cancer.
!  Cancer cells
–  start out as normal body cells,
–  undergo genetic mutations,
–  lose the ability to control the tempo of their
own division, and
–  run amok, displace other normal tissue
causing organ malfunction, death….
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Introduction
!  Understanding cell division, cell repair and cell “behavior” is
extremely important since it allows us the understand the
processes involved in health, disease and healing.
!  For example, two-thirds of
breasts tumor cells carry
receptors for estrogen.
!  The binding of estrogen
stimulates and enhances cell
division
!  Some breast cancer therapy thus
use estrogen receptor blockers
(such as Tamoxifen)
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Introduction
!  The more information known about the normal and abnormal
cell division, the better we can find specific therapies for
specific individuals
!  Understanding cell division and cell repair is extremely
important since it allows us the understand the processes
involved in health, disease and healing.
!  Research on the details of cell division and the regulatory
aspects of cell division will someday provide us with an
upper-hand in the battle against cancer
!  Someday we may be able to regenerate lost limbs like a seastar !?
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CELL DIVISION AND
REPRODUCTION
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8.1 Cell division plays many important roles in
the lives of organisms
!  Organisms (species) reproduce their own kind, a key
characteristic of life. It requires that each new cell we make
has all the information to remain true to it’s owner.
!  Everyone knows that flies make flies, frogs mate and make
more frogs, dogs will reproduce into dogs, you can’t turn a
donkey into a horse ,etc…
!  It is the concept of species and the continuation of the
species.
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8.1 Cell division plays many important roles in
the lives of organisms
!  The key issue is that all the information for a cell’s function
and how the species looks is located in the DNA.
!  The DNA is organized into chromosomes but the number
of chromosomes is only one aspect of the puzzle.
!  Example : all these species have 46 chromosomes
!  Homo sapiens
!  Lepus europaeus
!  Aplodontia rufa
!  Hippotragus niger
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8.1 Cell division plays many important roles in
the lives of organisms
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8.1 Cell division plays many important roles in
the lives of organisms
!  The chromosomes are made out of DNA and organized
into genes. The genes code for specific proteins.
!  It is the number of
genes , the quality of
the expressed proteins
and the overall
combination and
integration of these
proteins that
determines cell
function, tissue and
organ organization.
!  Small variations within
the genes result in the
different looks within a
species.
© 2012 Pearson Education, Inc.
8.1 Cell division plays many important roles in
the lives of organisms
!  Organisms thus reproduce their own kind, a key
characteristic of life. It requires that each new cell we make
has all the information to remain true to it’s owner.
!  In typical Cell Division, the result is two cells. Biologist
name them the off-spring cells or the daughter cells (it
does not mean the cells are females).
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8.1 Cell division plays many important roles in
the lives of organisms
!  One key issue is that all the information for a cell’s function
is located in the DNA.
!  Thus, the two new daughter cells need exact copies of the
DNA from the mother cell otherwise the new cells may not
function correctly
!  A typical cell division hence requires
–  the duplication of the DNA (chromosomes), and
–  delivery of the right copies (sorting of the new sets ) of
chromosomes into the resulting pair of daughter cells.
–  In addition, each daughter cell receives all the cytoplasmic
components required for cellular metabolism ( such as ribosomes,
mitochondria,….)
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8.1 Cell division plays many important roles in
the lives of organisms
!  A typical cell division is used
–  for reproduction of single-celled organisms,
–  growth of multicellular organisms from a fertilized egg
into an adult,
–  repair and replacement of cells
!  A special type of cell division is used for sperm
and egg production.
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Cell division plays many important roles in the
lives of organisms
!  Living organisms reproduce by two methods.
–  Asexual reproduction
–  involves inheritance of all genes from one (1) parent.
–  produces an offspring that is identical to the original cell or
organism; they become genetic copies of each other
–  This is for example a yeast cell,
producing a genetically identical
daughter cell by asexual
reproduction
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Prokaryotes reproduce by binary fission
!  Prokaryotes (bacteria and archaea) reproduce by
asexual reproduction called binary fission
(“dividing in half”).
!  The chromosome of a prokaryote is
–  a singular circular DNA molecule associated with
proteins and
–  much smaller than those of eukaryotes.
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Prokaryotes reproduce by binary fission
!  Binary fission of a prokaryote occurs in three stages:
1.  duplication of the circular DNA chromosome and
separation of the copies to opposite sides of the cell
2.  continued elongation of the cell and movement of the
copies, and
3.  division into two daughter cells by constriction; it
separates the plasma membrane so each new cell has
exactly the same genetic material.
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Plasma
membrane
Prokaryotic
chromosome
Cell wall
3
1
Duplication of the chromosome
and separation of the copies
2
Continued elongation of the
cell and movement of the copies
Division into
two daughter cells
Salmonella bacterium
undergoing binary
fission
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Prokaryotes reproduce by binary fission
!  When conditions are favorable such as the right
temperature and nutrients are available, some
bacteria like Escherichia coli can divide every 20
minutes.
!  This means that in just 7 hours one (1) bacterium
can generate 2,097,152 bacteria.
!  After one more hour the number of bacteria will have
risen to a colossal 16,777,216. That’s why we can
quickly become ill when pathogenic microbes invade
our bodies.
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Other asexual reproduction
!  Some eukaryotic cells, such
as yeast, reproduce by
budding
!  The buds grow into fully
matured individuals which
eventually break away from
the parent organism.
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Other asexual reproduction
!  A few multi-cellular
organism, such as
sponges, Hydra ( a
freshwater, sessile, jelly
fish relative) and corals
also create ‘off-spring”
by a budding principle.
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Hydra with bud
Brain coral with buds
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Cell division plays many important roles in the
lives of organisms
!  The other mode of reproduction
is called Sexual reproduction
–  In this process the genes from two
(2) individuals are mixed.
–  produces offspring that are similar to
the parents, but show variations in
traits
–  involves inheritance of unique sets
of combination of genes from two
parents.
–  creates offspring with new set of
“genetic cards” and new variations
on a similar theme.
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THE EUKARYOTIC CELL
CYCLE AND MITOSIS
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8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
!  Eukaryotic cells
–  are more complex and larger than prokaryotic cells,
–  have more genes, and
–  Whereas prokaryotes have one circular DNA, eukaryotes
store most of their genes on multiple chromosomes within
the membrane enclosed nucleus.
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8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
!  Eukaryotic chromosomes are composed of
chromatin consisting of
–  one long DNA molecule and
–  proteins that help maintain the chromosome structure and
control the activity of its genes.
–  When a cell is not dividing, the chromatin of every
chromosome is very relaxed and almost invisible with a
microscope.
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8.3 Chromosomes are composed of chromatin
In this uncoiled chromatin, the black arrows point at DNA wrapped around proteins
(histones). The white arrow indicates segments of DNA without proteins
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8.3 Chromosomes are composed of chromatin
A schematic representation of the previous slide
DNA wrapped around histone proteins
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8.3 Chromosomes are composed of chromatin
In this uncoiled chromatine, most of the proteins have
been stripped away
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8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
!  To prepare for division, the chromatin of each
chromosome becomes
–  highly compact, condensed and becomes visible with a
microscope.
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8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
!  Before a eukaryotic cell begins to divide, each
chromosome is duplicated exactly, resulting in
–  two copies called sister chromatids
–  The sister chromatids are joined together by a narrowed
“waist” called the centromere.
–  Since chromosomes are only “nice and visible” when they
are condensed, they have already duplicated. The
pictures of chromosomes thus are actually of sets of
sister chromatids (duplicated chromosomes)
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8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
sister chromatids
Chromosomes
duplicated right
before division
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8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
Highly visible chromatin
(chromosomes) in a plant cell (African
blood lily) just before cell division
(mitosis).
Visible chromatin of a bluebell plant
cell (Endymion sp.) undergoing cell
division (mitosis).
© 2012 Pearson Education, Inc.
8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
Sister
chromatids
!  Thus if a cell has “n”
chromosomes, they will
become duplicated and the
cell will have 2n sister
chromatids.
Centromere
!  Example : a cell has 10
chromosomes. When cell
division starts, each become
duplicated , resulting in 20
sister chromatids
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8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
Sister
chromatids
!  When a cell divides, the sister
chromatids
!  separate from each other, now
called chromosomes, and are sorted
into separate daughter cells.
!  This results in two daughter cells,
each containing a complete and
identical set of chromosomes
Centromere
!  In the previous example, the
sister chromatids become
separated and sorted into 2
daughter cells we obtain 2 cells
with new sets of 10 chromosomes
Figure 8.3B
Chromosomes
DNA molecules
Sister
chromatids
Chromosome
duplication
Centromere
Sister
chromatids
Chromosome
distribution
to the
daughter
cells
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