Tuesday
September 30, 2014

Homework Help: Mitosis

Posted by Mallory on Sunday, January 7, 2007 at 9:24am.

Hey! i want to know what is the importance of mitosis when it comes to growth, asexual reproduction and repair.

Thankkkksss in advance!

Thank you for using the Jiskha Homework Help Forum. Here is a great tutorial site from Arizona on mitosis:

http://www.biology.arizona.edu/Cell_bio/tutorials/cell_cycle/cells3.html

Here is a labeled diagram:

http://www.accessexcellence.org/RC/VL/GG/mitosis.html

It still doesn't answer my question

I've looked everywhere

still need help

Sorry! Hopefully this PDF from the BBC will help:

Cell Reproduction: Mitosis - 1
Growth and reproduction are two of the characteristics of life. The cell theory
states "All cells come from preexisting cells by a process of cell
reproduction, or cell division".
Mitotic cell division is the process by which all cells of a multicellular organism are
formed. Cell division is also responsible for repair and replacement of cells and
tissues during one's lifetime, and for asexual reproduction, a means of making
more individuals common in protists, fungi, many plants and some animals.
We know that all cells of an individual have exactly the same DNA, and their DNA
is found in structures called chromosomes. Each species has a fixed
chromosome number, a number that does not change from generation to
generation. The DNA must also stay the same from cell to cell within an organism,
so that when cells divide, new cells formed will have exactly the same DNA as the
original cell.
To ensure that chromosomes and DNA remain the same in new cells, the following
must take place when cells divide:
• We must form two new cells from the original cell.
• Since each cell must have all of the genetic material for the organism, we must
have a mechanism that exactly duplicates the DNA from the original cell and
distributes the copied DNA equally to the new cells. The distribution of DNA
into new nuclei during cell division is called mitosis. (Duplication of DNA is a
part of the discussion of structure and function of DNA.)
• We must also separate the cytoplasm, and critical organelles, such as
mitochondria and chloroplasts, of the original cell into the new cells formed so
that the new cells can survive, grow and function. The separation of cytoplasm
into new cells is called cytokinesis.
Mitotic cell division is the process by which all cells of a multicellular organism are
formed. Cell division is also responsible for repair and replacement of cells and
tissues during one's lifetime, and for asexual reproduction, a means of making
more individuals common in protists, fungi, many plants and some animals.
In our discussion of cell reproduction, we shall focus on the processes of cell
reproduction (mitosis and cytokinesis) in eukaryotic organisms. The process of
cell division in prokaryotic organisms, binary fission, has similarities, but the
single molecule of DNA and absence of a nucleus in the prokaryotic cell account for
a number of differences in the "mechanics" of the process.
In addition, in sexually reproducing organisms, a variation of cell reproduction,
called meiosis, occurs at one stage in the organism's life cycle (to form gametes
in animals, or to start the gamete producing stage in plants). We will discuss the
process of meiosis later.
Cell Reproduction: Mitosis - 2
Before discussing how cells divide, it's probably useful to discuss the
structure of chromosomes and chromosome terms (of which there are
a sufficiency).
Structure of Chromosomes
Chromosomes are composed of DNA and protein, a mixture called chromatin.
During the normal metabolic activities of the cell the collective DNA, or chromatin,
appears dense and grainy.
DNA is a thread-like double chain of nucleotides. The DNA coils around the histone
proteins to form nucleosomes. Chromosomes continue to tightly coil and fold
back on themselves prior to cell division. Chromosomes are visible only when
tightly coiled.
Each species has a characteristic number of chromosomes. Humans have 46
chromosomes; potatoes and chimpanzees have 48 chromosomes. The pea plant,
important in Mendelian genetics has 14, the even more famous fruit fly has 8.
Some ferns have chromosome numbers exceeding 1000. Chromosomes are selfduplicating
and must do so prior to each cell division. There is an essential
vocabulary associated with chromosome appearance before and after duplication.
Cell Reproduction: Mitosis - 3
Chromosome Terms before and after Duplication
• An unduplicated chromosome is one chromosome. A chromosome more or
less consists of two arms that extend from a centralized region called the
centromere.
• When a chromosome duplicates, it becomes one duplicated chromosome,
and the two copies remain attached to each other. It is still one
chromosome. The two exact copies of the duplicated chromosome, which
remain attached at the centromere region, are called "sister" chromatids.
They are identical to each other. (Remember this; it is essential!)
• At the centromere region of the duplicated chromosome, there are structures
(made of protein and DNA) called kinetochores. The kinetochores attach to
microtubules of the spindle during mitosis.
• After the identical sister chromatids are separated during mitosis, each (called
a "daughter" chromosome now) becomes a single unduplicated chromosome
again.
Rule to remember: A chromatid must be attached to its identical chromatid and
the two sister chromatids comprise one duplicated chromosome (not a pair of
chromosomes – "chromosome pair" is used for something else). "Sister"
chromatids are not two chromosomes. They are one duplicated
chromosome that consists of two identical chromatids. The only time you
can use the word chromatid is when you have the two identical chromatids
attached to each other.
Cell Reproduction: Mitosis - 4
The Cell Cycle
Mitosis is a part of the cell cycle. The cell cycle starts when a cell is formed
and continues until it divides (or dies). Some cells never divide; others are
specialized for division (especially in plants, where virtually all cell division occurs in
specialized tissue called meristem). Cell division is a brief part of the life cycle;
most of the life of a cell is spent in normal activities of growth and maintenance.
The cell cycle involves the following:
Interphase
Interphase is the period of time for normal cell activities, including:
• Growth (G1 or Gap)
The newly formed cell does its normal activities.
• DNA Duplication (S)
• DNA duplication (or synthesis) occurs.
• Once started, DNA duplication cannot be reversed; the cell is committed to
divide.
• Preparation for Division (G2)
• Proteins needed to do cell division are manufactured in preparation for
mitosis and cytokinesis.
• Cells can continue to grow and do their normal cell activities as well.
• A G2 checkpoint controls whether or not the cell will go into mitosis.
Note: If a cell never divides, it stays in G1 gpermanentlyh a state
called G0 (or non-dividing state).
Interphase
Cell Division (or cell reproduction), which includes:
• Mitosis
• Process of distributing the duplicated DNA equally to two new nuclei.
• Mitosis is divided into 4 stages
Prophase
Metaphase
Anaphase
Telophase
• Cytokinesis
• Process of separating the cytoplasm contents of the original cell into two
new cells.
Cell Reproduction: Mitosis - 5
The events of the cell cycle are carefully regulated at checkpoints in the cycle.
Cells that stay in G0 for example, never receive the appropriate signal at the G1
checkpoint to proceed into DNA synthesis. There are additional checkpoint signals
in G2 and during mitosis. One is at the start of anaphase.
The Stages of Mitosis
Mitosis is a continuum. Humans have decided to separate the process into stages
for the convenience of our discussion. Some humans even separate the stages
into sub-stages and intermediate stages.
Properly, mitosis refers to what happens to the chromosomes in the nucleus.
Cytoplasmic division occurs during the accompanying cytokinesis.
The Spindle Complex
Since chromosomes are being distributed into new nuclei, a critical component of
the process of mitosis is how the chromosomes are moved. Movement of
chromosomes involves sets of microtubules, known as the spindle apparatus.
Microtubules of the spindle complex extend from each pole of the cell and overlap
each other at the equator of the cell. Poisons that affect microtubule function
block cell division. Spindle formation is one of the events of prophase.
Cell Reproduction: Mitosis - 6
Prophase
Chromosome Condensation
• Duplicated chromosomes start to condense and tightly coil to become visible as
threadlike structures as prophase starts. Chromosomes continue to condense
and become thicker as prophase progresses.
• The nucleolus region (an aggregation of chromosome bits and concentrated
RNA and protein) of the nucleus will disassociate.
• The duplicated chromosomes are firmly attached at their centromeres
throughout the condensation and coiling.
Nuclear membrane
• The nuclear membrane degrades in later prophase into small vesicles, which can
be used to synthesis new nuclear membrane material in the new cells.
Microtubule Organization
• Microtubules initiate spindle formation and determine the poles of the cell. The
spindle apparatus will extend from the poles of the cell to the center of the cell
surrounding the nuclear region and to the opposite pole of the cell.
• Some microtubules from each pole of the cell attach to each duplicated
chromosome's kinetochores located in the centromere region.
• Other microtubules overlap each other from the poles through the equator
region of the cell.
• In many cells, clusters of microtubules form around the centriole pairs, which
replicated during interphase. Microtubules move centriole pairs to the
respective poles of the dividing cell. These regions are sometimes called the
asters. Centrioles are not essential to mitosis. Cells that lack centrioles still
form the spindle complex. It's just a way to ensure that the new cells will have
a pair of centrioles in their cytoplasm.
Prophase
Note: some researchers choose to call the events that include the degradation of
the nuclear membrane and the attachment of the spindles to chromosomes
prometaphase.
Cell Reproduction: Mitosis - 7
Metaphase
• The spindle apparatus moves the chromosomes to the equator of the cell,
aligning the centromeres of each duplicated chromosome along the equator.
• Chromosomes are moved by a combination of pulling and pushing of spindle
microtubules.
• The length of the spindle microtubules is regulated by the kinetochores to
facilitate the alignment of centromeres at the equator.
• The ultimate alignment of chromosomes along the equator plane of the cell is
metaphase, and the chromosomes are often called the metaphase plate.
Metaphase
Anaphase
• Centromeres of each duplicated chromosome separate to start anaphase. You
can't actually see this; the separating chromosomes are the first visual sign of
anaphase.
• Kinetochore motor proteins pull their chromosomes along the spindle
microtubules from the equator to the poles of the cells. The microtubules
disintegrate behind the moving chromosomes, becoming shorter.
• The overlapping polar microtubules lengthen moving the poles of the cell
further apart, and, in animal cells elongating the cell.
• Since sister chromatids are identical, each of the two clusters of
chromosomes being pulled to the two poles of the cell has one copy of each
original chromosome. As the chromosomes are pulled toward the poles, they
begin to lengthen out.
Anaphase
Cell Reproduction: Mitosis - 8
Telophase
• The spindle microtubules disperse and the spindle apparatus disappears.
• Chromosomes stretch back out and become indistinct as chromatin.
• Membrane vesicles form new nuclear membranes around each group of
chromosomes (at the two poles).
• Each new nucleus has chromosomes identical to the original cell and the same
number of chromosomes as the original cell.
Telophase
Mitosis in Blood Lily
Mitosis in Whitefish Blastula
Cell Reproduction: Mitosis - 9
Cytokinesis: Separation of the Cytoplasmic Contents
Mitosis describes events of chromosomes and nuclei. Most cells accompany
mitosis with cytokinesis, the separation of the cytoplasm of the original cell into
two new cells. This is not always the case. Some organisms (including many fungi
and algae) are "multinucleate", they just have one cell body with many nuclei. Some
animal tissues are also multinucleate.
Cytokinesis coincides with the events of telophase or occurs immediately after, so
that at the completion of mitosis, the original cell is separated into two cells, each
with a nucleus and DNA identical to that of the original cell. Although the end
result of cytokinesis is always two new cells, the mechanism of separation is
different in plants and animals, so we shall discuss them separately.
Cytokinesis in Plant Cells
Each cell of a plant is surrounded by a rigid cell wall. During cytokinesis, new wall
material must be synthesized along with plasma membrane. The formation of the
new cell walls is called cell plate formation.
Cell plate formation involves making a cross wall at the equator of the original cell.
Golgi vesicles containing wall material fuse along microtubules forming a disk-like
structure called the phragmoplast or cell plate. As cellulose and other fibers
are deposited, the cell plate is formed creating a boundary and new cell wall
between the two new cells.
Membrane material from the original cell fuses to each side of the cell plate
forming new cell membranes on the dividing sides of the original cell.
Cytokinesis in Plant Cells
Cell Reproduction: Mitosis - 10
Cytokinesis in Animal Cells
The cells of animals lack cell walls. Cytokinesis in animal cells is started with the
formation of a cleavage furrow, a depression or pinching in of the plasma
membrane.
This is caused by a ring of microfilaments (the contractile ring), composed of
the protein, actin, which forms across the middle of the cell after the chromatids
are separated in anaphase. This ring contracts, pinching the membrane toward the
center of the cell, which eventually pinches the cell in two. The additional
membrane surface needed is supplied by membrane made during interphase.
Cytokinesis in Animal Cells
When and Where does Mitosis Occur? Cell Division in Perspective
Growth
All growth (increase in numbers of cells) in individual organisms takes place by
mitosis, from the fertilized egg (zygote) to death.
Replacement
Many cells are routinely replaced in organisms. This replacement of cells is done
by mitosis. For examples, we replace the cells that line our digestive tract every
one to three days.
Repair and Maintenance
Mitosis is used for repair and replacement of damaged cells or tissues, whenever
possible. This includes regeneration of lost parts for some organisms.
Cell Reproduction: Mitosis - 11
Non-Sexual (Asexual) Reproduction
Mitosis is used for all asexual reproduction or propagation. This is especially
common in plants, fungi and protists. Animals less commonly reproduce asexually.
There are many claims for the world's largest organism based on the ability to
make more. Asexual reproduction produces offspring genetically identical to the
original parent, as would be expected of any mitosis.
Asexual Reproduction in Yeast, Protist and Hydra (an Animal)
Cloning, a method of producing genetically identical offspring, uses mitosis,
precisely because mitosis duplicates the DNA exactly. Cloning is quite easy to do
with many plants; they are easily propagated non-sexually anyway. Many of the
agricultural products originate from cloned individuals, such as navel oranges.
Tissue culture is also a popular way of cloning plants. Most cells of plants retain
the ability to "dedifferentiate" and become embryonic-like. Most animal cells, once
specialized (or differentiated), cannot do so.
In many animals, cloning takes on a different meaning. The new organism takes a
nucleus from the "parent", but the nucleus is injected into an egg cell from that
species, from which the egg cell nucleus has been removed. The "clone" is then
implanted into a surrogate mother for development. Dolly, the sheep, is our most
famous mammal clone to date, because she was the first. Dolly is essentially
genetically identical to the individual from whom the nucleus was removed, but the
cytoplasm of the donor egg cell has some influence on early development and
especially in mitochondria.
The successful "cloning" of mammals has resulted in a flurry of research, and
speculation about cloning humans. This is one of the biological issues that has
serious ethical consequences. One of the reasons each of us should learn as much
as possible about biology is to make informed decisions about the ethical
applications of research. Cloning is discussed more extensively in the DNA unit.

If not, from the Regents Prep:

http://regentsprep.org/regents/biology/units/reproduction/asexual.cfm

I found a few others so let me know if you'd like those too. This is definitely NOT my area!

THANKS

Don't worry, i found the answers from what you've given me!

Thanks again!

i need help wit cell parts

what are the phases of mitosis

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