Transcript Bio09 Cell Division

Cell Division
Chapter 9
Cell Division
• Cell division is the process in which a cell
becomes two new cells.
• Cell division allows organisms to grow and to
reproduce.
Cell Division
• In single celled organisms cell division is the
method for increasing their numbers,
• In multicellular organisms, the process of cell
division leads to growth, the replacement of
lost cells, the healing of injuries, and the
formation of reproductive cells.
3 Types of Cell Division
• Binary Fission
• Mitosis
• Meiosis
Binary Fission
• Prokaryotic cells utilize binary fission.
• A single loop of DNA replicates, a membrane
forms in between the two molecules, and the
cell divides.
• The daughter cells are genetically identical to
the parent cell.
Mitosis
• Eukaryotic cells utilize mitosis.
• Eukaryotic cells have several chromosomes
that are replicated and divided.
• The daughter cells are genetically identical to
the parent cell.
Meiosis
• Eukaryotic cells also utilize meiosis to
reproduce daughter cells with half of the
genetic information of the parent cells.
Comparison of Mitosis and Meiosis
Asexual Reproduction
• Binary fission and mitosis are methods utilized
by single-celled organisms for asexual
reproduction.
• Only one parent cell is necessary.
Asexual Reproduction
• The parent cell divides and results in two
organisms that are genetically identical to the
parent.
• Most prokaryotes use binary fission.
• Most eukaryotic organisms are multicellular.
In multicellular organisms, mitosis produces
new cells.
Sexual Reproduction
• Sexual reproduction is the combining of
genetic information from two parents. This
results in a genetically unique individual.
• Meiosis is the process that produces the cells
for sexual reproduction.
Cell Cycle
• The cell cycle consists of all the stages of
growth and division for a eukaryotic cell.
• The cell cycle includes the stages in which the
cell spends its time engaged in metabolism.
Mitosis
Interphase
• Interphase is the longest stage of the cell
cycle.
• During this stage, the cell engages in
metabolic activities to prepare for the next cell
division.
• Interphase is broken down into 3 distinct
stages:
– G1, S, and G2
G1 Stage of Interphase
• During the G1 stage of interphase, the cell
gathers nutrients.
• This allows the cell to carry out its normal
functions and to grow in volume.
• If a cell stays in the G1 phase for an extended
period, it is often renamed G0 because the cell
is not moving forward in the cell cycle.
S Stage of Interphase
• During the S Stage of interphase, DNA
synthesis (replication) occurs.
• The DNA in chromosomes is wrapped around
histone proteins to form nucleosomes.
S Stage of Interphase
• The nucleosomes are then coiled to form
chromatin.
• As the chromatin becomes coiled, it becomes
visible as a chromosome.
• A chromatid is one of two parallel parts of a
chromosome.
Chromosome
DNA Synthesis
• Before DNA synthesis, each chromatid
contains one DNA molecule.
DNA Synthesis
• DNA synthesis occurs resulting in 2 DNA
molecules, one in each chromatid. Sister
chromatids are the 2 chromattids of the
chromosome that were produced by
replication.
• The sister chromatids are attached at the
centromere.
Chromosomes
G2 Stage of Interphase
• The final stage of interphase is G2.
• The cell makes all of the cellular components
that it will need for division.
• The chromatin has replicated, but has not
coiled, so it is not visible.
Mitosis
• There are two distinct events in Mitotic cell
division:
– 1. The replicated genetic information of the cell is
equally distributed in mitosis.
– 2. After mitosis, the cytoplasm of the cell divides
into two new cells. This division is called
cytokinesis (cell splitting).
Stages of Mitosis
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Prophase
Metaphase
Anaphase
Telophase
Prophase
• Chromosomes condense.
• Spindle and spindle fibers form.
• Nuclear membrane disassembles.
Prophase
Metaphase
• Chromosomes align at the equatorial plane of
the cell.
Metaphase
Anaphase
• Sister chromatids move toward opposite ends
of the cell.
Anaphase
Telophase
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Spindle fibers disassemble.
Nuclear membrane re-forms.
Chromosomes uncoil.
Nucleolus re-forms.
Cytokinesis
• After telophase, the cell has two nuclei.
• Cytokinesis creates two daughter cells.
• Cytokinesis is the process whereby the
contents of the cell are split between the two
daughter cells.
Cytokinesis
• Animal cells form a cleavage furrow, which is
an indentation of the plasma membrane that
pinches in towards the center of the cell.
• In plant cells, a cell plate begins to form at the
center of the cell.
• Cytokinesis marks the end of a round of cell
division. The cell then returns to interphase at
G1.
Determination and Differentiation
• Determination is the cellular process of
determining the genes a cell will express when
mature.
• A cell commits to becoming a certain cell type.
• When a cell reaches the end of this path, it is
said to be differentiated. It has become a
particular cell type.
Cell Division and Sexual
Reproduction
• Meiosis is a form of cell division that aids
sexual reproduction.
• Mitosis is responsible for growth and repair of
tissues.
• Meiosis is responsible for the production of
eggs and sperm.
• The cells of sexually reproducing organisms
have two sets of chromosomes and thereby
two sets of genetic information.
Cell Division and Sexual
Reproduction
• One set is received from the mother’s egg and
the other set from the father’s sperm.
• Therefore, gametes containing only one set of
chromosomes must be formed.
• Haploid cells carry only one complete copy of
their genetic information.
• Diploid cells carry two complete copies of
their genetic information.
Cell Division and Sexual
Reproduction
• In many sexually reproducing organisms,
meiosis takes place in the gonads.
• The gonads in females are known as ovaries.
The gonads in males are know as testes.
Cell Division and Sexual
Reproduction
• A gamete is a reproductive cell like eggs and
sperm. They are also referred to as germ
cells.
• Fertilization is the joining of genetic material
from two haploid cells.
Meiosis
Meiosis
Meiosis I
• Meiosis I is a reduction division, in which the
chromosome number in the two cells
produced is reduced from diploid to haploid.
• The sequence is divided into four phases:
– Prophase I, metaphase I, anaphase I, and
telophase I.
Prophase I
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Chromosomes condense.
Spindle and spindle fibers form.
Nuclear membrane disassembles.
Synapsis and crossing-over occur.
Metaphase I
• Chromosomes align on equatorial plane as
synapsed pairs.
Anaphase I
• Homologous chromosomes separate from
each other.
• Chromosomes move towards cell’s poles.
• Reduction occurs.
Telophase I
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Spindle fibers disassemble.
Chromosomes uncoil.
Nuclear membrane re-forms.
Nucleoli reappear.
Meiosis II
• The two daughter cells formed from Meiosis I
both continue through Meiosis II so that four
cells result.
• Meiosis II includes four phases:
Meiosis II
– Prophase II, metaphase II, anaphase II, and
telophase II.
• No DNA replication occurs between telophase
I and meiosis II.
• The events in the division sequence of meiosis
II are the same as those that occur in meiosis.
Meiosis
Prophase II
• Chromosomes condense.
• Spindle and spindle fibers form.
• Nuclear membranes disassemble.
Metaphase II
• Chromosomes align in an unpaired manner.
Anaphase II
• Chromatids separate as chromosomes begin
to move to the cell’s poles.
Telophase II
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Nuclear membrane re-forms.
Chromosomes uncoil.
Nucleoli reappear.
Spindle fibers disassemble.