Download Mitosis and Meiosis

1/9/2015
LIMITS TO CELL GROWTH
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Mitosis and Meiosis
Cell growth and division
The larger the cell, the more trouble the cell
has moving nutrients and waste across the
cell membrane.
LIMITS TO CELL GROWTH
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1. DNA/information overload – As a cell
increases in size, it does not make extra
copies of its DNA.
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LIMITS TO CELL GROWTH
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2. Exchanging materials – materials enter and exit
a cell through the cell membrane.
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Cell size is limited by its DNA, if the cell gets
too big the DNA would no longer be able to
serve the needs of the cell.
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LIMITS TO CELL GROWTH
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Ratio of Surface Area to Volume
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Surface area – L x W x number of sides
Volume – L x W x H
LIMITS TO CELL GROWTH
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If a cell has a length of 1 cm, width of 1 cm,
height of 1 cm, and 6 sides,
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its surface area would be 6 cm2
its volume would be 1 cm3
Surface area – the total area of the cell membrane
The rate at which materials can be exchanged depends
on the surface area.
The rate at which materials are used up and waste is
produced depends on the cell’s volume.
The ratio of surface area to volume in this
example cell would be 6:1.
If the cell increase in size, its volume
increases faster than the surface area.
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This makes it more difficult for the cell to move
needed materials in and waste products out.
Goal of the cell: have a large ratio of
surface area to volume.
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Prevention from getting too
big
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Before a cell gets too big, it will split or
divide in half.
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Genes
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A parent cell forms two new daughter cells.
A cell must copy all its DNA before division
to ensure that each cell is the same, thus
each daughter cell has their own copy of
DNA, both identical to the other.
DNA contains the
information needed to
direct a cell’s activities.
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DNA is composed of genes
– segments of DNA that
encode a protein.
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Prokaryotic chromosomes
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Most prokaryotes have a single circular
DNA molecule, or chromosome.
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Chromosomes—structures that contain the genetic
information that is passed on from one generation of
cells to the next.
Found in the cytoplasm of prokaryotes.
Folded into a space about 1/1000th smaller than a
prokaryote’s length.
Eukaryotic chromosomes
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Most eukaryotes have
as much as 1,000
times the amount of
DNA as prokaryotes.
Eukaryotic DNA is
primarily located in the
nucleus in the form of
multiple
chromosomes.
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Chromosome structure
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Eukaryotes have
even more DNA so
the cell had to have
a way to fit it all in
the nucleus.
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Are transmitted info from
parent to offspring.
1 DNA strand contains 1000’s
of genes.
DNA molecules are
extremely long.
Chromosome structure
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Nucleosomes – Beaded structure
composed of multiple histones with
associated DNA.
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During mitosis the histones cause the fibers
of the chromosome to coil up and packed into
the structures that you can see.
Chromosomes
contain both DNA
and proteins.
Chromatin – DNA
that is tightly coiled
around proteins
called histones.
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Chromosome structure
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Chromosomes are 40% DNA and 60%
protein.
Chromosomes copy themselves during
DNA replication forming sister
chromatids.
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Chromosomes must copy themselves so that
the new cell gets the same info as the old cell.
Sister chromatids are attached by a
centromere.
PROKARYOTIC CELLS SIMPLY
SPLIT
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Bacteria are prokaryotes lacking nuclei.
Bacterial DNA is a circular chromosome.
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PROKARYOTIC CELLS SIMPLY
SPLIT
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DNA unzips making 2 strands and each strand
is copied giving 2 identical copies of DNA.
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EUKARYOTIC CELL CYCLE
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Eukaryotic cells have a nucleus, so they must
undergo nuclear division.
Cell cycle – repeating sequences of growth and
division through which many kinds of eukaryotic
cells pass.
Bacterial cell grows and then splits into
equal halves.
This is called binary fission.
Product of binary fission – 2 identical bacterial
cells.
INTERPHASE
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G1 – rapid cell growth, a cell is in this part
of the cell cycle for the longest period of
time between cell divisions.
S – DNA is copied, chromosome replicated
is now two sister chromatids joined at
centromere.
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INTERPHASE
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CELL CYCLE - MITOSIS
G2 – Organelles replicate, microtubules are
reassembled to form spindle apparatus that
will move chromosomes, cell is now
prepared for mitosis. This is the shortest
phase of interphase.
An eukaryotic cell spends most of its time in
Interphase.
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CYTOKINESIS
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MITOSIS
Cytokinesis – the division of the cytoplasm.
This is the last step of cell division.
After cytokinesis is complete, the cell will be
in Interphase again.
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PROPHASE
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Chromosomes condense
and become visible.
Centrioles form and take up
positions on opposite ends of
the nucleus.
Spindle becomes visible.
Nuclear membrane breaks
down, and the nucleolus
disappears.
Mitosis – the process by which the nucleus
of a cell is divided into two nuclei, each with
the same number of chromosomes.
Misconception – mitosis IS NOT cell
division, it is a part of cell division!
Biologists divide the events of mitosis into
four phases:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
METAPHASE
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Spindle fibers assist in moving the
chromosomes to the equator
(middle) of the cell.
The centromeres of all the sister
chromatids line up.
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The imaginary line that bisects each
of the chromatids through the
centromere is called the metaphase
plate.
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TELOPHASE
ANAPHASE
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Sister chromatids separate from
each other at the centromere.
The spindle now pulls each
chromosome to opposite ends of
the cell (toward the centrioles).
The spindle is taken apart as the
chromosomes move.
Each pole now has one complete
set of chromosomes.
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Chromosomes uncoil,
spindle fibers
disappear, and the
nuclear membrane
reforms.
Mitosis is complete.
CYTOKINESIS
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Cytoplasm of original cell is split in half.
Cell membrane grows to enclose both cells.
Animal cells pinch in the membranes
forming a cleavage furrow.
Plant cells form a cell plate to split the
cytoplasm.
CYTOKINESIS (continued)
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Plant cells form a cell plate at the equator of the
cell where new cell wall forms on both sides of
the plate.
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The product is two identical cells.
Following cytokinesis, the cell re-enters
interphase at the G1 phase, and the cell cycle
continues.
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The plate is formed from secretions of the golgi.
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