Transcript Cell_Division_mitosis

Cell Division
How to make more
Review
What are the parts of a
chromosome?
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DNA
DNA
(Deoxyribonucleic
Acid)
 is the chemical
whose building block
sequence encodes
the information that a
cell uses to construct
a particular protein.
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Genes
A Gene is a sequence of DNA that
instructs a cell to produce proteins
 It is the unit of inheritance
 The variants of a gene are called Alleles
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Structure of a Chromosome
 A Chromosome
is a highly coiled
and condensed strand of DNA
wrapped around proteins called
histones
 A Chromosome
is made from a
single strand of DNA and contains
many genes.
Structure of a Chromosome
A Chromatid – A single, very condensed strand
of DNA. Half of a chromosome.
 A Centromere – The largest constriction in a
chromosome.
 A Kinetichore – The area of the chromosome
where the spindle fibers attach.
 A Nucleosome – DNA wrapped around a
histone
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Chromosome Parts
The Link Between DNA Replication and Chromosome Duplication
DNA is Condensed into Visible Chromosomes Only For Brief
Periods in the Life of a Cell
95% of the time, chromosomes are
like this.
Easily visible chromosomes are
apparent perhaps 5% of the time in
an actively growing cell and less in a
non-growing cell.
Why do we need to make more
cells?
1.
2.
3.
Growth
Repair
Reproduction
What would happen if we could not make
new cells?
Types of Cells
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Somatic cells
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Body cells
46 chromosomes
Diploid (2n)
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Germ Cells
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Sex Cells
23 chromosomes
Haploid (n)
The Cell Cycle
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Regular sequence of growth and division.
Cell
cycle rates vary
A brain cell may never divide
Embryos divide rapidly
This is a continuous process that we
study in steps
Interphase
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Interphase is the major stage of cell division where
the cell is not dividing.
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Interphase is divided into 3 phases
 G1
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Cell is making protein, carbohydrates, and lipids.
Time in G1 varies greatly.
(Synthesis phase)
Cell replicates it’s DNA.
Proteins that make the spindle fibers are produced.
Microtubules form structures called centrioles near the
nucleus.
 G2
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(Gap phase 1) - Growth
(Gap phase 2)
Division preparation
Cell makes more proteins for membranes of daughter cells
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Two Types of Cell Division
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Mitosis
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Meiosis
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The division of two
somatic (non-sex) cells
Produces two identical
daughter cells.
Daughter cells have the
same number of
chromosomes as the
parent cell
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We will learn about this
later
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Stages of Mitosis: Prophase
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Microtubules
assemble to form
spindle
Nuclear membrane
breaks down
Nucleus no longer
visible
DNA is condensed
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Metaphase
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Chromosomes
attach to spindle at
their centromeres.
They line up at the
center of the cell.
When they split,
each daughter cell
receives one
chromatid from
each replicated
chromosome
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Spindle Equator
Anaphase
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Cell membrane
indents at middle
Centromeres part
and chromatids
move to opposite
ends of the cell
Cell stretches
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Telophase
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Spindle falls apart
Nuclear membranes
form
Cytokinesis –
organelles
distributed between
two daughter cells
Cells separate
Diploid cells - the
two daughter cells
have the same
number of
chromosomes as the
original parent cell
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Cytokinesis – Division of
Cytoplasm
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Plants
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Cell plate
Vesicles line up and fuse
Cellulose accumulates
Fuses with plasma
membrane
Middle
Lamella
Animals
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Cleavage furrow
Cytoplasm pinches at
spindles previous
midpoint
Done using cytoskeleton
Plants Do It Differently
Cancer
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Control mechanisms govern the rate of cell division
Cancer is essentially a disease of mitosis - the
normal 'checkpoints' regulating mitosis are over-ridden
A single cell is transformed, or converted from a
normal cell to a cancer cell.
Often due to a DNA mutation that occurs in one of
several genes that normally functions to control
growth.
Once these crucial Cell Cycle genes start behaving
abnormally, cancer cells start to proliferate wildly by
repeated, uncontrolled mitosis.
It’s not a Tumor – oh but it is!
Tumors - The cancer cells proliferate to
form mass of cancer cells called a tumor.
 As the tumor grows larger, it begins to
release proteins from the cell to attract
new blood vessel growth (this is called
angiogenesis).
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Kinds of Tumors
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Benign:
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tumor cells remain at original site.
Can be removed surgically or killed by radiation, usually
eliminating any further cancer development at that site.
Malignant:
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tumor cells send out signals that tell the body to produce a
new blood vessel at the tumor site.
These cells have their own food, oxygen supply, and a way
to travel through the body using the blood vessels
Cells spread to surrounding tissues (via the bloodstream or
lymph) and start new tumors = metastasis.
Usually surgery is performed to remove the tumor, followed
by radiation and chemotherapy.
Contact Inhibition
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Cells normally stop dividing when they
become crowded
HeLa cells
 Named after woman who donated them 40
years age
 The cells have 70-80 chromosomes and
are immortal
 Most studied cells
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Cancer Is One Outcome of A Runaway Cell Cycle
Licentious division - prostate cancer cells during division.
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Benign
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Malignant
Meiosis
Meiosis is the type of cell division by which
gametes (eggs and sperm) are produced.
 Meiosis involves a reduction in the
amount of genetic material.
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Diploid to haploid
 46 to 23 chromosomes
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Meiosis comprises two successive nuclear
divisions with only one round of DNA
replication.
Homologous Chromosomes
Pair of chromosomes that are similar in
length, shape, and genetic assortment
 Line up with each other during meiosis
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Meiosis 1
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Interphase:
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Before meiosis begins, genetic material is
duplicated.
Prophase 1:
Duplicated chromatin condenses, spindle forms
 Each chromosome consists of two, closely
associated sister chromatids.
 Crossing-over can occur during the latter part of this
stage.
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 Chiasmata
– visible manifestations of crossing-over
Meiosis 1
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Metaphase 1:
 Spindle fibers attach
 Homologous chromosomes align at the equatorial
plate.
 Called tetrads – formed by a synaptonemal complex
 Crossing-over can occur during this stage.
Anaphase 1:
 Homologous pairs separate with sister chromatids
remaining together.
Telophase 1:
 Two daughter cells are formed with each daughter
containing only one chromosome of the homologous
pair.
Meiosis 2
Prophase 2:
 DNA does not replicate.
 Metaphase 2:
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Anaphase 2:
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Chromosomes align at the equatorial plate.
Centromeres divide and sister chromatids
migrate separately to each pole.
Telophase 2:
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Cell division is complete. Four haploid
daughter cells are obtained.
Oogenesis
The creation of an ovum (egg cell).
 Only one egg is produced by meiosis
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The three polar bodies disintegrate
Spermatogenesis
Spermatogenesis is the process of sperm
cell development
 You make four fully functional sperm cells
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Independent Assortment
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The random
separation of
homologous
chromosomes during
Anaphase 1
The chromosomes line
up randomly
50/50 chance at each
chromosome
8 million possible
combinations for
humans
Crossing-over
The non-sister chromatids with in the
homologous pair twist around each other
and rebind to the opposite chromatid
 It results in genetic recombination
 Another source of variation in people
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Random fertilization
8 million varieties from dad
 8 million from mom
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8 mil * 8 mil = a lot of variety
Non-disjunction
the failure of chromosome pairs to
separate properly during cell division.
 Can happen in either meiosis 1 or 2
 The result is one gamete with too many
chromosomes and one lacking in
chromosomes
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Usually leads to a disorder
Types of Non-disjunction
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Monosomy
Lacking one or more chromosomes
 Most zygotes do not survive
 Example: Turner syndrome
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Trisomy
One extra chromosome
 Example: Downs syndrome
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Disorders of Non-disjunction
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Abnormalities in chromosome numbers
typically kill the zygote before a woman
even knows she is pregnant.
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A Zygote is a diploid cell resulting from the
fertilization of an ovum.
Triple X syndrome
 Kleinfelter syndrome
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Down’s Syndrome – Trisomy 21
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Results from the non-disjunction of
chromsome 21
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Offspring will have three of chromosome 21
Down’s Syndrome – Trisomy 21
Down’s syndrome is a genetic disorder
that includes a combination of birth defects
 A range of mental retardation
 Short stature
 Characteristic facial features
 Heart defects
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Patau syndrome - Trisomy 13
Severe mental retardation
 Cleft lip and cheek plate
 Extra finger on each hand
 Malformation of the eyes and ears
 Small head and other abnormalities
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Edwards Syndrome - Trisomy 18
Mental retardation
 Defects in hands and head
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Klinefelter Syndrome (XXY)
Occurs in males
 Taller than normal
 May have below average intelligence
 Are almost always sterile
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Jacobs syndrome (XYY)
Occurs in males
 Larger than normal
 Borderline intelligence
 Have mild to sever behavioral
disturbances
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Turner Syndrome (X)
Occurs in women
 Usually under 5 ft tall
 Have webbing of the neck
 Have under developed ovaries
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Genetic Screening
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What is available?
Carrier screening
Prenatal diagnostic
testing
Newborn to adult
screening
Prenatal testing
Identifies chromosomal abnormalities
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Chorionic Villi
Take a tiny piece from
the placenta
Preformed in early
pregnancy – 10-13
weeks
There is a very small risk
of miscarriage
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Amniocentesis
Take a sample of the
amniotic fluid – the fluid
around the baby in the
uterus
Preformed between 16 –
20 weeks
The risk of miscarriage
is almost non-existent
Chorionic Villi
Amniocentesis
PKU (Phenylketonuria)
Test newborn children for PKU deficiency
 Lack an enzyme needed to metabolize
amino acids phenylalanine and tyrosine
 A build up of these can cause mental
retardation and seizures
 Children can be put on a special diet low
in those amino acids to prevent mental
retardation in this case
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Genetic Screening
Would you want to know?
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Advantages
Preventative care
Cheaper to treat prior to
development of the
disorder
Know if you are a gene
carrier for a disorder
Choice
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Disadvantages
Insurance companies
may not want to cover
you
Public knowledge and
prejudice
Possible higher
abortion rates