Download Lab. 2 Cell Division 1. Mitosis Division

Lab. 2
Cell Division
1. Mitosis Division
Main topics:
•
Cell cycle definition
•
What’s Mitosis?
•
karyokinesis division
•
Cytokinesis division
The Cell Cycle definition:
Each eukaryotic cell has a repeating set of events
that make up the life of every cell, called the cell cycle.
Although they vary in length depending upon the cell's
function, the cell cycle for all cells can be described in five
steps. The first three steps where the cell grows, matures,
and carries out its life function are collectively called
interphase, followed by mitosis, and cytokinesis.
Figure (2): Cell cycle
1- Interphase:
The cell is engaged in metabolic activity and performing it’s prepare for mitosis.
Chromosomes are not clearly discerned in the nucleus, although a dark spot called the
nucleolus may be visible. The cell may contain a pair of centrioles (or microtubule
organizing centers in plants) both of which are organizational sites for microtubules.
It is divided into three phases that lead up to and include nuclear division, and it
will explain below:
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The G1 stage
A lot of protein synthesis happens in order to increase the amount of cytosol in the cell.
Cytosol is the liquid inside the cell, but outside the organelles, that contains the cell's
proteins. Proteins are the molecular machines that sustain the cell’s day-to-day
activities. The increase in cell size happens not just because more proteins are being
made, but also because the cell absorbs nutrients.
•
The S stage
Stands for "Synthesis". (“Synthesis”) is the time when the DNA is replicated, when the
chromosome goes from having one chromatid to having 2 chromatids held together at
the centromere.
•
The G2 stage
The cell prepares to enter mitosis. The DNA has already been duplicated during the S
phase, so the G2 phase is when the organelles of the cell need to duplicate. Not only
will the duplicated DNA be evenly divided during cell division, but so will the organelles.
Some organelles, such as mitochondria and chloroplasts, are discrete units that do not
bud off from larger organelles. Discrete organelles increase in number by undergoing
their own division during G2.
•
Checkpoints
The advantage of having three phases in interphase is that it allows time to check that
things are happening as they should. Three checkpoints exist during interphase, during
which the cell makes sure that everything has gone as planned and, if needed, fixes
errors. The G1-S checkpoint at the end of the G1 phase makes sure that the DNA is
intact and that the cell has enough energy to enter the S phase. The S phase
checkpoint makes sure that DNA is replicated correctly without any breakages. The G2M checkpoint at the end of the G2 phase is another safeguard in case something
happens to the DNA or cell before it undergoes the massive task of dividing.
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2- Mitosis
A process that takes place in the nucleus of a dividing cell, involves typically a series of
steps consisting of prophase, metaphase, anaphase, and telophase, and results in the
formation of two new nuclei each having the same number of chromosomes as the
parent nucleus.
Figure (3): Mitosis Phases.
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Phases of mitosis division
Phase
Drawing
1. Prophase:
Chromatin in the nucleus begins to
condense and becomes visible in the light
microscope as chromosomes. The
nucleolus disappears. Centrioles begin
moving to opposite ends of the cell and
fibers extend from the centromeres.
2. Metaphase:
Spindle fibers align the chromosomes along
the middle of the cell nucleus. This line is
referred to as the metaphase plate. This
organization helps to ensure that in the next
phase, when the chromosomes are
separated, each new nucleus will receive
one copy of each chromosome.
3. Anaphase:
The paired chromosomes separate at the
kinetochores and move to opposite sides of
the cell. Motion results from a combination
of kinetochore movement along the spindle
microtubules and through the physical
interaction of polar microtubules.
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Microscope
4. Telophase:
Chromatids arrive at opposite poles of cell,
and new membranes form around the
daughter nuclei. The chromosomes
disperse and are no longer visible under
the light microscope. The spindle fibers
disperse, and cytokinesis or the partitioning
of the cell may also begin during this stage.
Cytokinesis division:
Cytokinesis division in Animal cells
In
animal
Cytokinesis division in plant cells
cells,
In plant cells, the
results
rigid wall requires
when a fiber ring
that a cell plate be
composed
synthesized
cytokinesis
of
a
protein called actin
between
around the center of
daughter cells.
the
cell
contracts
pinching the cell into two daughter
cells, each with one nucleus
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the
two
References:
http://biothemes.wikifoundry.com/page/Cytokinesis+-+Plant+vs.+Animal+Cell
http://commons.wikimedia.org/wiki/File:Mitosis_%28261_14%29_Pressed;_root_meristem_of_onion_%28cells_in_prophase,_anaphase%29.jpg
http://classroom.synonym.com/list-3-steps-occur-during-interphase-17577.html
http://www.merriam-webster.com/dictionary/mitosis
http://www.infoplease.com/cig/biology/cell-cycle-interphase-mitosis-cytokinesis.html
http://w3.marietta.edu/~biol/introlab/Onion%20root%20mitosis.pdf
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Training
Preparing the root tip squash.
1. Transfer a root to the center of a clean
microscope slide and add a drop of water.
2. Using a razor blade cut off most of the
unstained part of the root, and discard it.
3. Cover the root tip with a cover slip, and then
carefully push down on the cover slide with the
wooden end of a dissecting probe. Push hard,
but do not twist or push the cover slide sideways.
The root tip should spread out to a diameter
about 0.5 – 1 cm.
Onion root tip squash
1. Find and draw a cell showing each
stage of mitosis
Prophase
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Metaphase
Anaphase
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Telophase
Exercise 2
1- Describe all of the phases:
1- ........................................
2- ........................................
3- ........................................
4- ........................................
5- ........................................
6- .........................................
2- Choose the right answer:
1. What is the name of the microtubule fibers that pull the sister chromatids
apart?
A. Centromeres
B. Membranes
C. Ligands
D. Spindles
2. What is the name of the structures responsible for generating the spindle
fibers?
A. Centromeres
B. Membranes
C. The funky hot chocolates
D. Centrioles
3. The pinching off of the cell membrane that creates two new cells (after mitosis)
is called
A. Interphase
B. Metaphase
C. Anaphase
D. Cytokinesis
4. What is the name of the attachment point between sister chromatids in a
chromosome?
A. Centrioles
B. Centromeres
C. Spindles
D. Membranes
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