Download Cell Division Video Binary Fission

1/14/2010
Cell Division Video
Chromosomes & Cellular
Reproduction
Ch 6 & 7.1
pg. 118-132 & 144-151
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Biology
Mrs. Stolipher
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Formation of New Cells by Cell
Division
• Cell division, also called cell reproduction, occurs in
humans and other organisms at different times in
their life.
• The formation of gametes involves yet a special
type of cell division. Gametes are an organism’s
reproductive cells, such as sperm or egg cells.
• When a cell divides, the DNA is first copied and
then distributed.
Prokaryotic Cell Reproduction
• Prokaryotes reproduce by a type of cell division
called binary fission.
• Binary fission is a form of asexual reproduction that
produces identical offspring.
• In asexual reproduction, a single parent passes
exact copies of all of its DNA to its offspring.
• Binary fission occurs in two stages: first, the DNA is
copied (so that each new cell will have a copy of
the genetic information), and then the cell divides.
• Eventually the dividing prokaryote is pinched into
two independent cells.
Binary Fission
Eukaryotic Cell Reproduction
• A gene is a segment of DNA that codes for a protein or RNA molecule.
• When genes are being used, the DNA is stretched out so that the
information it contains can be used to direct the synthesis of proteins.
• As a eukaryotic cell prepares to divide, the DNA and the proteins
associated with the DNA coil into a structure called a chromosome.
• The two exact copies of DNA that make up each chromosome are called
chromatids.
• The two chromatids of a chromosome are attached at a point called a
centromere.
• The chromatids, which become separated during cell division and placed
into each new cell, ensure that each new cell will have the same genetic
information as the original cell.
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Gene
Chromosome Structure
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Parts of a Chromosome
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How Chromosome Number and
Structure Affect Development
Sets of Chromosomes
Comparing Cell Division in
Prokaryotes and Eukaryotes
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Homologous Chromosomes
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• Homologous chromosomes are chromosomes that
are similar in size, shape, and genetic content.
• Each homologue in a pair of homologous
chromosomes comes from one of the two parents.
• The 46 chromosomes in human somatic cells are
actually two sets of 23 chromosomes.
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Sets of Chromosomes
• When a cell, such as a somatic cell, contains two
sets of chromosomes, it is said to be diploid.
Comparing Haploid and Diploid
Cells
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• When a cell, such as a gamete, contains one set
of chromosomes, it is said to be haploid.
• The fusion of two haploid gametes—a process
called fertilization—forms a diploid zygote. A
zygote is a fertilized egg cell.
Chromosome Number of Various
Organisms
Sex Chromosomes
• Autosomes are chromosomes that are not directly involved in
determining the sex (gender) of an individual.
• The sex chromosomes, one of the 23 pairs of chromosomes in
humans, contain genes that will determine the sex of the individual.
• In humans and many other organisms, the two sex chromosomes
are referred to as the X and Y chromosomes.
Change in Chromosome Number
Karyotype
• Humans who are missing even one of the 46 chromosomes do not
survive.
• Humans with more than two copies of a chromosome, a condition
called trisomy, will not develop properly.
• Abnormalities in chromosome number can be detected by analyzing a
karyotype, a photo of the chromosomes in a dividing cell that shows
the chromosomes arranged by size.
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Chromosome Number
Change in Chromosome Structure
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• Changes in an organism’s chromosome structure
are called mutations.
• Breakage of a chromosome can lead to four
types of mutations:
1. deletion mutation
2. duplication mutation
3. inversion mutation
4. translocation mutation
Types of Chromosome Mutations
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The Life of a Eukaryotic
Cell
The Cell Cycle
• The cell cycle is a
repeating sequence of
cellular growth and
division during the life
of an organism.
• A cell spends 90
percent of its time in
the first three phases
of the cycle, which are
collectively called
interphase.
• The five phases of the cell cycle are:
Control of the Cell Cycle
1. First growth (G1 = Gap 1) phase During the G1 phase, a
cell grows rapidly and carries out its routine functions.
• The cell cycle has key checkpoints (inspection points) at which
feedback signals from the cell can trigger the next phase of the
cell cycle (green light).
2. Synthesis (S) phase A cell’s DNA is copied during this
phase.
• Other feedback signals can delay the next phase to allow for
completion of the current phase (yellow or red light).
3. Second growth (G2 = Gap 2) phase In the G2 phase,
preparations are made for the nucleus to divide.
• Control occurs at three principal checkpoints:
1. Cell growth (G1) checkpoint This checkpoint makes the
decision of whether the cell will divide.
4. Mitosis The process during cell division in which the
nucleus of a cell is divided into two nuclei is called mitosis.
2. DNA synthesis (G2) checkpoint DNA replication is checked at
this point by DNA repair enzymes.
5. Cytokinesis The process during cell division in which the
cytoplasm divides is called cytokinesis.
3. Mitosis checkpoint This checkpoint triggers the exit from
mitosis.
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When Control Is Lost: Cancer
Control of the Cell Cycle
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• Certain genes contain the information necessary
to make the proteins that regulate cell growth
and division.
• If one of these genes is mutated, the protein may
not function, and regulation of cell growth and
division can be disrupted.
• Cancer, the uncontrolled growth of cells, may
result.
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Forming the
Spindle
Chromatid Separation in Mitosis
• During mitosis, the chromatids on each
chromosome are physically moved to opposite
sides of the dividing cell with the help of the
spindle.
•
When a cell enters the
mitotic phase, the
centriole pairs start to
separate, moving toward
opposite poles of the cell.
•
As the centrioles move
apart, the spindle begins
to form.
• Spindles are cell structures made up of both
centrioles and individual microtubule fibers
that are involved in moving chromosomes
during cell division.
Separation of Chromatids by Attaching Spindle Fibers
• The chromatids are moved to each pole of the
cell in a manner similar to bringing in a fish with a
fishing rod and reel.
• When the microtubule “fishing line” is “reeled
in,” the chromatids are dragged to opposite
poles.
• As soon as the chromatids separate from each
other they are called chromosomes.
Interphase
• Includes G1, S, & G2
phases of cell cycle
• Rest & growth stage
where cell doubles in
size, duplicates all
organelles & DNA
• Happens before mitosis
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Prophase
Mitosis
•
•
•
Is a period of nuclear division
Produces 2 identical daughter cells each
containing a complete set of chromosomes
Is made up of 4 phases
1.
2.
3.
4.
Prophase
Metaphase
Anaphase
telophase
• Is the 1st & longest phase
of mitosis
• Individual chromosomes
become visible
• Nuclear membrane &
nucleolus disappear
• Centrioles appear &
migrate to opposite poles
• Spindle forms
Video Clip
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Anaphase
Metaphase
• Centromere splits
• Spindle fibers shorten
• Sister chromatids are
pulled to opposite
poles (sides)
• Chromosomes attach
to spindle fibers at
their centromeres
• Chromosomes line up
at the equator (center
of cell)
Anaphase
Metaphase
Video Clip
Video Clip
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Telophase
• Is the reverse of
prophase
• Chromosomes uncoil
& become less visible
• Spindle disappears
• Nuclear membrane
reforms
• Nucleolus reappears
Telophase
Cell plate
Mitosis
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Video Clip
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Cytokinesis
• As mitosis ends, cytokinesis begins.
Comparing Cell Division in Plants and Animals
In Animals
In Plants
• the cytoplasm of the cell is divided in half and the
cell membrane grows to enclose each cell,
forming two separate cells as a result.
• The end result of mitosis and cytokinesis is two
genetically identical cells where only one cell
existed before.
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Results of Mitosis
• produces 2 new daughter cells that are identical
in structure & function to the original parent cell
• In unicellular organisms = 2 new organisms
• In multicellular organisms = groups of cells that
work together as a tissue
Chapter 7
Diploid vs. Haploid
• Human body (somatic) cells have 46 chromosomes –
23 pairs
• 1 chromosome in each pair came from Dad & the
other one came from Mom
• This type of cell is called diploid
– It has 2 of each kind of chromosome
– Abbreviated 2n
•Gametes (egg & sperm) only have one of each kind
of chromosome – in humans 23 chromosomes
- this type of cell is called haploid
Mitosis Video Quiz
• Take out a sheet of paper & number 1-5
Formation of Haploid Cells
• Meiosis is a form of cell division that halves the
number of chromosomes when forming
specialized reproductive cells, such as gametes or
spores.
• Meiosis involves two divisions of the nucleus—
meiosis I and meiosis II.
• Before meiosis begins, the DNA in the original cell
is replicated. Thus, meiosis starts with
homologous chromosomes.
- abbreviated n
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8 Stages of Meiosis
Meiosis I
Prophase I The nuclear envelope breaks
down. Homologous chromosomes
pair. Crossing-over occurs when
portions of a chromatid on one
homologous chromosome are
broken and exchanged with the
corresponding chromatid portions of
the other homologous chromosome.
Metaphase I The pairs of homologous
chromosomes are moved by the
spindle to the equator of the cell.
Anaphase I The chromosomes of each
pair are pulled to opposite poles of
the cell by the spindle fibers.
Telophase I Individual chromosomes
gather at each of the poles. In most
organisms, the cytokinesis occurs.
MEIOSIS I: Homologous chromosomes separate
Meiosis II
INTERPHASE
Prophase II A new spindle forms
around the chromosomes.
Metaphase II The chromosomes line
up along the equator and are
attached at their centromeres to
spindle fibers.
Anaphase II The centromeres divide,
and the chromatids (now called
chromosomes) move to opposite
poles of the cell.
Telophase II A nuclear envelope forms
around each set of chromosomes,
PROPHASE I
Centrosomes
(with
centriole
pairs)
Nuclear
envelope
METAPHASE I
Microtubules
Sites of crossing over
attached to
Spindle kinetochore
Chromatin
Sister
chromatids
Tetrad
ANAPHASE I
Metaphase
plate
Centromere
(with kinetochore)
Sister chromatids
remain attached
Homologous
chromosomes separate
and the cell undergoes cytokinesis.
Meiosis Video Clips
MEIOSIS II: Sister chromatids separate
TELOPHASE I
AND CYTOKINESIS
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II
AND CYTOKINESIS
Prophase I
Video Clips\Prophase_One.asx
Video Clips\Metaphase_One.asx
Metaphase I
Cleavage
furrow
Anaphase I
Telophase I
Sister
chromatids
separate
Haploid
daughter cells
forming
Video Clips\Anaphase_One.asx
Video Clips\Telophase_One.asx
Prophase II
Video Clips\Prophase_Two.asx
Metaphase II
Anaphase II
Video Clips\Metaphase_Two.asx
Video Clips\Anaphase_Two.asx
Telophase II
Meiosis Video
Video Clips\Telophase_Two.asx
Comparing Meiosis and Mitosis
MITOSIS
MEIOSIS
PARENT CELL
(before chromosome replication)
PROPHASE
Video Clips\Meiosis.asx
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Duplicated
chromosome
(two sister chromatids)
METAPHASE
Site of
crossing over
MEIOSIS I
PROPHASE I
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Tetrad formed
by synapsis of
Chromosome
Chromosome
homologous
replication
replication
chromosomes
2n = 4
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Chromosomes
Tetrads
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align at the
align at the
ANAPHASE
TELOPHASE
2n
Daughter cells
of mitosis
metaphase plate
metaphase plate
Sister chromatids
separate during
anaphase
Homologous
chromosomes
separate
during
anaphase I;
sister
chromatids
remain together
2n
No further
chromosomal
replication; sister
chromatids
separate during
anaphase II
METAPHASE I
ANAPHASE I
TELOPHASE I
Haploid
n=2
Daughter
cells of
meiosis I
MEIOSIS II
n
n
n
n
Daughter cells of meiosis II
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Independent Assortment
Meiosis and Genetic Variation
The random distribution of homologous chromosomes during meiosis is
called independent assortment.
• Meiosis is an important process that allows for
the rapid generation of new genetic
combinations.
• Three mechanisms make key contributions to
this genetic variation:
1. independent assortment
2. crossing-over
3. random fertilization
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Crossing-Over and Random
Fertilization
• Meiosis and the joining of gametes are
essential to evolution. No genetic process
generates variation more quickly.
• The DNA exchange that
occurs during crossing-over
adds even more
recombination to the
independent assortment of
chromosomes that occurs
later in meiosis.
• The pace of evolution is sped up by genetic
recombination. The combination of genes
from two organisms results in a third type, not
identical to either parent.
• Thus, the number of genetic
combinations that can occur
among gametes is
practically unlimited.
• Furthermore, the zygote
that forms a new individual
is created by the random
joining of two gametes.
Importance of Genetic Variation
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