Download Ch 9 Mitosis

Mitosis
Chapter 9 How Cells Divide
Chromosome Structure
 During
cell division, the DNA in Eukaryotic cells
are coiled into compact structures called
chromosomes
 Chromosomes are rod-shaped structures made of
DNA (40%) & protein (60%)
Chromosome Structure
Histones
 DNA
is tightly wound around proteins called
histones
 Histones help maintain the shape of the
chromosome and aid in the tight packing of DNA
 Non-histone proteins are generally involved in
controlling the activity of specific regions of the
DNA
Parts of a Chromosome
Chromosomes exist as 2
identical half. Each half is
called a chromatids
 Chromatids form as DNA
makes a copy of itself
before cell division
 2 chromatids are held
together by a Centromere
until they separate during
cell division

Parts of a Chromosome
 Regions
of DNA uncoil in between cell division so
they can be read and so information can be used to
direct the activities of the cell
 The less tightly coiled DNA-protein complex is
called chromatin.
Prokaryotic vs Eukaryotic
chromosomes
 DNA
in most prokaryotes comprise only 1
chromosome which is attached to the inside of the
cell membrane
 Prokaryotic chromosomes consist of a circular
DNA molecules associated with proteins
 Same as eukaryotic, must be very compact to fit
into the cell
Chromosome Numbers

Each specie has a
characteristic number
of chromosomes
Sex Chromosomes
 Human
and animal chromosomes are categorized
as sex chromosomes or autosomes
 Sex chromosomes determine the sex of an
organism & they may also carry genes for other
characteristics
 Normal females are XX
 Normal males are XY
Autosomes
 Autosomes
are the body cells. They make up the
first 22 chromosomes
 Also called somatic cells
 Every cell of an organism produced by sexual
reproduction has 2 copies of each autosome.
 The organism receives one copy from each parent
called homologous chromosomes
Homologous Chromosome
 Homologous
Chromosomes:
paired chromosomes with genes
for the same traits arranged in the
same order.
 Sister Chromatid: two halves of
the doubled structure
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Homologous
chromosomes
Centromere
Homologous chromosomes
Replication
Sister
Sister
chromatids chromatids
Karyotype
 Is
a photomicrograph of the chromosomes in a
dividing cell found in a normal human
 46 chromosomes exist as 22 homologous pairs of
autosomes and 2 sex chromosomes
Diploid & Haploid
Cells having 2 sets of chromosomes are diploid
 Diploid cells have both chromosomes for each
homologous pair
 Diploid cells also have 2 sex chromosomes in animals &
many other organisms
 All normal human cells (except sperm & egg cells) are
diploid cells
 Abbreviated as 2n
 In humans the # of chromosomes is 46 -22 pairs of
autosomes, 1 pair of sex chromosomes.

Diploid & Haploid
 Human
sperm & egg cells are haploid cells
 Abbreviated n or 1n [when a sperm cell 1n & egg
cell 1n combine, the new cell will be diploid 2n]
 These cells contain only 1 set of chromosomes
 Haploid cells have half the number of
chromosomes that are present in diploid cells
 Human haploid cells have only 1 chromosome of
each homologous pair & only 1 sex chromosomes
Cell Division
All cells are derived from the division
of preexisting cells.
Cell division is the process where
cells produce offspring cells
In eukaryotes, cell division differs
indifferent stages of an organisms life
cycle
Organisms reproduce by cell division
ASEXUAL REPRODUCTION
Binary fission is similar in
function to mitosis.
 Asexual
reproduction is the creation of
offspring from a single parent.
 Binary
fission produces two daughter cells
genetically identical to the parent cell.
parent cell
DNA
duplicates
cell begins
to divide
daughter
cells
Prokaryotes
 Prokaryotes
divide through binary fission
Binary Fission consist of 3 stages
1.
2.
3.
The chromosome attached to the inside of the
cell membrane makes a copy of itself resulting in
2 identical chromosomes
Cell continues to grow until it is 2x the cells
original size
Cell wall forms between the 2 chromosomes and
the cell splits into 2 new cells
Some eukaryotes reproduce through
mitosis.
 Budding
forms a new organism from a small
projection growing on the surface of the parent.
Hydra
bud
Yeast
 Fragmentation
is the splitting of the parent
into pieces that each grow into a new
organism.
• Vegetative reproduction
forms a new plant from the
modification of a stem or
underground structure on
the parent plant.
How Big are YOUR Cells?
Some cells like a RBC
average in size of 8um in
diameter
 Nerve cells can reach
lengths of 1 m but have
small diameters


The cell with the largest
diameter is the yoke of the
ostrich egg measuring 8
cm
Why are cells limited to size?
1.
2.
3.
Diffusion limits cell size
DNA limits cell size
Surface Area to Volume Ratio limits cell size
Cell Reproduction
 Remember
in the Cell Theory states:
1. All cells come from preexisting cells
 Cell
division is the process by which new cells are
produced from one cell
 Cell division results in two cells that are identical
to the original, parent cell.
As we go over this…
 Right
now…cells in
your body are
growing, dividing,
and dying
 Old are being shed &
replaced, cuts &
bruises are healing.
The Cell Cycle
 The
events that occur
during the cell cycle
are a continuous
process
 2 major Groups Make
the Cell Cycle
1. Interphase
2. Mitosis
Interphase
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M
Metaphase
Prophase
Anaphase
Telophase
C
G2
Interphase (G1, S, G2 phases)
Mitosis (M)
S
Cytokinesis (C)
G1
Interphase
 Not
a true phase of mitosis, but prepares the
cell for division
 Interphase, the busiest phase of the cell
cycle, is divided into three parts.
Interphase
S phase
DNA synthesis
and replication
G1
Rapid
growth
and
metabolic
activity
Centrioles replicate;
cell prepares for
division
During Interphase
Period of Growth for the cell by protein synthesis
 Cells spend most of their life in interphase
1. G1 Phase-Cells Grow
2. S Phase-DNA Replication
3. G2 Phase-Cell prepares for division (makes more
organelles or materials necessary for division)
 GO Phase-Some cells will exit G1 and go into Go-Cells do
not replicate DNA and do not prepare for division
Example-nerve cell

G = Gap Time
 Offspring
cells grow to mature size
 G1 stands for time gap following cell division &
preceding DNA replication
 G2 stands for the time gap following DNA
synthesis (s phase)
Interphase
Plant cell
Animal Cell
Interphase: the resting stage
Interphase Video Clip
Mitosis
 Mitosis
is the division of the nucleus or
genetic material of a cell.
 Mitosis is followed by the division of the
cytoplasm: Cytokinesis
 Steps
of Mitosis
Prophase, Metaphase, Anaphase
& Telophase
Plant More Apple Trees!
Prophase
 The
longest phase of mitosis
 Double Chromosomes appear
 Centrioles replicate
 Spindle fibers appear
 Chromosomes attach to spindle fibers by
the Centromere
 Nucleus, Nuclear membrane & nucleolus
break down
 Nucleus, Nuclear Envelope & Nucleolus
disappear
2
pairs of dark spots called centrosomes appear
next to the disappearing nucleus
 In animal cells, each centrosome contains a pair of
centrioles
 As centrosomes separate, spindle fibers radiate
from the centrosome
 In plant cells, the centrosomes lack centrioles
2 types of spindle fiber make up the
mitotic fibers
1. Kinetochore fibers-go from centriole to
centromere of chromosome
2. Polar fibers-go from pole to pole
Prophase
Prophase
PROPHASE
PLANT CELL
ANIMAL CELL
Prophase:
The First Stage of Mitosis
PROPHASE VIDEO CLIP
Metaphase
 Kinetochore
fibers move the chromosomes to the
center of the cell
 Each chromosome is held in place by the
kinetochore fibers
 Chromosomes (paired chromatids) attach to the
spindle fibers by their Centromere and line up at
the equator
Metaphase
METAPHASE
PLANT CELL
ANIMAL CELL
Metaphase:
The Second Stage of Mitosis
METAPHASE: VIDEO CLIP
Anaphase
 Chromatids
separate at the Centromere and begin
to migrate to opposite poles
 Centromeres lead the way
 Chromatids cluster together when they reach the
poles
 Each chromatid is considered to be an individual
chromosome
 Cleavage furrow forms
Anaphase
Anaphase
ANAPHASE
PLANT CELL
ANIMAL CELL
Anaphase:
The Third Stage of Mitosis
ANAPHASE: VIDEO CLIP
Telophase
Chromosomes at opposite poles
 Chromosomes uncoil & form Chromatin
 Nuclei forms around chromatin
 Nucleus, Nucleolus, Nuclear Envelope & Nuclear
Membrane re-appear
 Cytokinesis happens
 Spindle disappears
 2 new cells identical to original cell

Animal cells: Cleavage
 Plant cells: grow a new cell wall

Telophase
TELOPHASE
PLANT CELL
ANIMAL CELL
Cytokinesis
 Division
of the ________________
 Begins in Telophase
 A cleavage furrow forms in animal cells at the
equator
 A cell plate forms in plant cells and will become
the cell wall
Cytokinesis
See Author Notes
Telophase:
2 New Daughter Cells
Telophase:
The Last Phase of Mitosis
TELOPHASE VIDEO CLIP
Plant vs Animal Mitosis
 Both
have centrosomes-but only the animal cells
have centrioles
 Cleavage in animal cells during cytokinesis and
growth of a new cell wall in plants
Cancer and Control of the Cell
Normal Control of the Cell Cycle
 The
cell cycle is controlled by proteins called
cyclins and a set of enzymes that attach to the
cyclin and become activated
 Occasionally, cells lose control of the cell cycle
Loss of Control
 This
uncontrolled dividing of cells can result from
the failure to produce certain enzymes, the
overproduction of enzymes, or the production of
other enzymes at the wrong time.
 Cancer
is a malignant growth resulting from
uncontrolled cell division
Cancer
 Currently,
scientists consider cancer to be a result
of changes in one or more of the genes that
produce substances that are involved in controlling
the cell cycle
 Cancerous cells form masses of tissue called
tumors that deprive normal cells of nutrients
 Cancer
cells form disorganized clumps called
tumors.
– Benign tumors remain clustered and can be removed.
– Malignant tumors break away (metastasize), and can
form more tumors.
normal cell
cancer cell
bloodstream
Cancer
Cancer is the leading
cause of death in the US
exceeded by heart
disease
 Can affect any tissue in
the body
 Lung and Breast Cancer
rate among the highest

Death Rate of Cancer
Most common:
Breast, Lung, Prostate, Colon & Skin
Liver Cancer
The causes of Cancer
 The
causes of cancer are difficult to pinpoint
because both genetic and environmental factors are
involved
 Cancer may also be caused by viral infections that
damage the genes
The causes of Cancer
 1.
Inherited errors in specific genes
- Breast cancer
 2. Exposure to radiation or chemicals
- Skin cancer
 3. Some carried by viruses
- Cervical cancer
 4. Environmental factors
- pollution, tobacco
Cancer Prevention

Diets low in fat and high
in fiber content can reduce
the risk of many kinds of
cancer.
Vitamins and minerals
may also help prevent
cancer
 Daily Exercise
