Stages of Interphase
The first stage of interphase is the G1 phase. The two daughter
cells start to speed up its pathway after mitosis. The mitosis slows
down the biochemical pathway. Nutrients in the system can slow the
G1 phase, or even stop it all together. In this happens then the cell
won’t be able to complete the cell division process. The main thing
happening during this stage is the cell us starting grow and replicate
itself. The cells grows due to the protein synthesis, this allows the cell
to grow up to double in size.
The second phase of interphase is the S phase. The very first
stage of this phase is replication of the DNA. During this the cell is
also going to continue to grow to a larger size. Also the chromatids
are copied while in the S phase. This copy give you a chromatid and
its sister chromatid which, when combined, gives you chromosomes.
The chromosomes are then checked for any error that may have
happened during the duplication process. They do this by coiling and
condensing the chromosomes.
The last phase of interphase is the G2 phase. During this phase
cell proteins are synthesized. This synthesis process is completely
necessary for the cell to divide. The next step is when the
chromosomes start to deflate or shrinks in size. Also during this phase
of interphase the proteins that are required for the buildup of the
spindles are synthesized. At the end of the G2 phase the
chromosomes in the cell become completely visible. This is when the
cell enters prophase, the first stage of mitosis.
http://wiki.answers.com/Q/
What_are_the_three_stages_in_interphase&altQ=Three_stages_of_in
terphase&isLookUp=1
Cancer
According to scientist and doctors, cancer starts with changes in a
cell or a group of cells. It usually takes many years before you can
feel a lump, or when it shows up in a scan. The cells start to divide
and go through mitosis uncontrollably. If you compared normal cells
to cancer cells, cancer cells seem to have less vital control systems.
This is because some genes in the cells have been damaged or lost
due to mutation.
When a cell mutates it may lose or damage proteins that help
control its behavior. For example, a protein that controls and limits
cell reproduction may be permanently switched off. Carcinogens are
substances that can cause cancer. Tobacco smoke is a strong
carcinogen just to name one. There are many more carcinogens like
alcohol, arsenic, chewing tobacco, UV radiation, pesticide, certain
hair dyes, certain hair bleaches, and formaldehyde.
There are three different types of genes that can make a cell
cancerous. Genes that make the cell multiply called oncogenes, genes
that stop the cell from multiplying called a tumor suppressor, and
genes that repair damaged genes called DNA repair genes.
Oncogenes encourage the cells to go through mitosis. This usually
does not happen with adults. In most adults, cells would only multiply
to repair damage such as a wound, but when the genes become
abnormal, the cells multiply all the time. oncogenes really mean
''cancer genes''
Tumor suppressor genes control the cells and tell it when to stop
multiplying. They also help prevent cancer by encouraging other cells
with damaged proteins to destroy themselves. When these genes are
damaged or destroyed, the cell keeps multiplying uncontrollably. It
eventually turns into a tumor. In most cancers, the tumor suppressor
genes are missing.
DNA repair genes normally repair other genes that are damaged.
When these genes are damaged, other damaged genes are not
repaired. The mutated cell can then freely multiply itself along with
the cancerous mutations it developed. These DNA repair genes have
been found damaged in some cancers which include bowel cancer.
h"p://cancerhelp.cancerresearchuk.org/about-­‐cancer/what-­‐is-­‐cancer/cells/how-­‐cancer-­‐starts
Cells that stay in the G0 phase
The G0 is the phase in a cell in which it goes through permanent
rest. This means that the cells are forever in interphase and do not go
through mitosis. Stem, heart, brain, nerve, and muscle cells are
examples of this.
stem
Brain
heart
nerve
muscle cell
Skin cells on the other hand, only stay in interphase for 22 hours. It
also only stays in mitosis for 30 minutes to and an hour.
Facts
1. When cells die, they are eaten by white blood cells to dispose of
them.
2. Cancer damages genes in a cell and makes it grow uncontrollably.
3. Most human cells go divide every 24 hours.
Anaphase
Metaphase
Interphase
Chapter 3: Mitosis Purpose of Mitosis: produces the cells of the
body. When they split they produce identical cells
with a complete set of DNA. They are exactly like
their parents. It only has one division and that
leads to two cells.
What type of cells goes into this process? : Despite
differences between prokaryotes and eukaryotes, there are
several common features in their cell division processes.
Replication of the DNA must occur. Segregation of the
"original" and its "replica" follow. Cytokinesis ends the cell
division process. Whether the cell was eukaryotic or
prokaryotic, these basic events must occur.
Regulation of the cell cycle is accomplished in several ways. Some
cells divide rapidly. Others, such as nerve cells, lose their
capability to divide once they reach maturity. Some cells, such as
liver cells, retain but do not normally utilize their capacity for
division. Liver cells will divide if part of the liver is removed. The
division continues until the liver reaches its former size.
Cancer cells are those which undergo a series of rapid divisions
such that the daughter cells divide before they have reached
"functional maturity". Environmental factors such as changes in
temperature and pH, and declining nutrient levels lead to
declining cell division rates. When cells stop dividing, they stop
usually at a point late in the G1 phase, the R point
The phases of mitosis:
Interphase:
The interphase, or growth, period of the cell cycle (indicated by
"I" in the figure at right) alternates with mitosis. It's the time
when the cell isn't undergoing division. So it isn't part of
mitosis.
When this stage of the cycle begins, the chromosomes have
not yet replicated, but by the beginning of prophase replication
is complete, so that each chromosome is composed of two
sister chromatids. Replication occurs during the synthesis, or S
phase.
S phase is preceded by G phase, which in many cells is a time
when cell growth occurs. From G, a cell may exit the cell cycle
and go into a long-term stable state known as G where the cell
functions but does not divide.
At the beginning of the third stage of interphase, G phase,
replication is complete. During G the cell prepares for mitosis
as it undergoes rapid growth.
Prophase:
But as mitosis begins, the nuclear envelope starts to break up
and disappear. Each chromosome has replicated during
interphase and is therefore composed of two sister chromatids
containing identical genetic information.
Early during prophase, the first stage of mitosis, the
chromosomes become visible with a light microscope as they
condense begins to extend outward from each of the two
centrosomes. These starlike configurations composed of
radiating microtubules.
After the nuclear envelope has disappeared, proteins bind to
the centromeres to make the kinetochores. Microtubules attach
at the kinetochores and the chromosomes begin to move.
Metaphase:
By the end of prophase, the nuclear envelope has entirely
vanished and the chromosomes have condensed. In addition,
the microtubules of the spindle apparatus have attached to the
centromeres at their kinetochores. The centrosomes are now at
opposite ends ("poles") of the cells. Now, during metaphase —
the second stage of mitosis in the eukaryotic cell cycle — the
chromosomes, pulled by the spindle fibers, line up along the
middle of the cell, halfway between the centrosomes on an
imaginary plane called the metaphase (or equatorial) plate.
The chromosomes are now maximally condensed.
In mitosis, individual replicated chromosomes, each composed
of two sister chromatids, move to the equatorial plate during
this step (whereas during the first division of meiosis, pairs of
replicated chromosomes (tetrads) line up at this stage).
Anaphase:
During metaphase, the spindle fibers (or "microtubules")
attach themselves to the centromere of each chromosome.
Specifically, the connection is to specialized regions called
kinetochores within the centromeres. Each chromatid has one
kinetochore. Now, during anaphase, the two sister chromatids
of each chromosome are pulled apart by the spindle and
dragged by their kinetochores toward opposite poles of the
cell. The movement results from a shortening of the spindle
microtubules. Each chromosome† is pulled along by its
centromere. Formally, this phase begins when the duplicated
centromeres of each pair of sister chromatids separates, and
the resulting "daughter chromosomes" begin moving toward
the poles. As the separated chromosomes move away from
each other toward the poles, the cell elongates and the poles
themselves move further apart.
Telophase:
During telophase, the last stage of mitosis, the chromosomes
have reached the poles and they begin to uncoil and become
less condensed. Two new nuclear envelopes begin to form
around each of the two separated sets of unreplicated
chromosomes. At the same time there is division of the
cytoplasm (cytokinesis). In animal cells, a cleavage furrow —
an indentation around the equator of the cell — appears. By
the end of telophase, the cell has divided in two along the
plane defined by the furrow. In terrestrial plants, instead of a
cleavage furrow, a cell plate forms halfway between the two
separated sets of chromosomes, dividing the cell into two
daughter cells.
How many chromosomes are in a human parent
cell and daughter cell? 46/ 23
Resources
http://www.emc.maricopa.edu/faculty/farabee/biobk/
biobookmito.html
http://www.macroevolution.net/telophase.html
Meiosis 1
Describe each step of Meiosis 1:
Meiosis has 2 main purposes:
1. It is the reduction division, so it reduces the number of
chromosomes in half making
the daughter cells haploid, when the parent cell was diploid.
2. It is during meiosis I that most of the genetic recombination occurs.
Phases:
Before meiosis begins, the DNA undergoes replication, just like it did
before mitosis started.
So, when you first see chromosomes in meiosis I, they have sister
chromatids, just like in
mitosis.
Prophase 1: During prophase, DNA condensation occurs. The nuclear
envelope and
nucleoli disappear and the spindle starts to form. As DNA condensation
proceeds and the
chromosomes first become visible, they are visible as tetrads. So tetrads
become visible
during prophase.
Metaphase 1: In Metaphase, tetrads line up at the equator. The spindle
has completely
formed. It is during prophase 1 and metaphase 1, that genetic
combination is beginning.
Anaphase 1: Tetrads pull apart and chromosomes with 2 chromatids
move toward the
poles.
Telophase 1:Chromosomes with 2 chromatids decondense and a
nuclear envelope
reforms around them. So, now each nucleus is a haploid.
Why is crossing over important?
Crossing over is a very important event in meiosis 1 because it
allows variation in the
produced offspring may have certain traits from each parent.
Meiosis
What is the purpose of meiosis?
The purpose of meiosis is to increase the genetic variation. Meiosis is to reduce the normal
diploid cells, which are 2
copies of each chromosome per cell, to haploid cells, called gametes, which are 1 copy of each
chromosome. After
meiosis there are four haploids, each with different sets of chromosomes. However, in mitosis the
end results are two
identical diploids. Meiosis is used in sexual reproduction, since to reproduce, an egg, which is the
female, and a
sperm, which is the male, have to come together for reproduction to occur. This increases the
genetic variation that
allows for evolution and the adaptation of organisms to different environments.
How many viable cells are produced by males? Females? What are the resulting cells called?
Normal egg cells form after meiosis and are haploid, with half as many chromosomes as their
mother's body cells.
Haploid individuals, however, are usually non-viable, and the offspring usually has the diploid
chromosome number.
If the chromosome number of the haploid egg cell is doubled during the development, then the
offspring is "half a
clone" of its mother. If the egg cell was formed without meiosis, it is a full clone of its mother.
Explain what would happen to the total number of chromosomes if meiosis did not occur?
•
•
If meiosis did not occur, how many chromosomes would humans have
after five
generations?
Provide illustration and URL
If meiosis didn't occur then cells wouldn't be able to reproduce. So you couldn't be able to
produce an organism.
Human cells, with their full set of 46 chromosomes, are diploid. Gametes have a haploid
number, 23. When
conception occurs, a human sperm and ovum combine their chromosomes to make a zygote,
which is a fertilized
egg, with 46 chromosomes. This is the same number that the parents of each had in their
somatic cells. Each
generation inherits the same number of chromosomes. Without reducing their number by half in
meiosis, each new
generation would first have double the number of chromosomes in their cells as the one before.
Within only 15
generations, humans would have over 1 million chromosomes per cell and would be a different
kind of animal.
MEIOSIS I
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http://tchefty.edublogs.org/2011/06l0B/meiosis-2-5-4-1-4-21
(with kinetochore)
ANAPHASE
I
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TElOPHASE I
AND CYTOKINESIS I
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Meiosis 1
Vocabulary:
Chromosome: an organized structure of DNA and protein
found in cells.
Chromatid: one-half of two identical copies of a replicated
chromosome.
Crossing over: the exchange of genetic material between homologous
chromosomes that occur during
meiosis and goes to genetic variability.
Tetrad: a 4 part structure during meiosis.
Spindle Fiber: protein structures that pull apart genetic material in a cell
when it divides.
Centrioles: barrel-shaped cell structure that are found in animal eukaryotic cells
most of the time.
Parent Cell: the cell giving rise to the daughter cells by cell division.
Daughter Cell: when a cell divides it makes two new cells called daughter cells.
Diploid: a cell that contains only two sets of
chromosomes.
Meiosis
I
hase
Interphas
e
Me
tap
Early Prophase
Anaphase
Pro
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Telop
hase
Resources:
websites where I got information for this project on meiosis:
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio
2010 1/bioo/020 1 01 0/020Iectures/meiosis/meiosis. htm
http://www.cellsalive.com/meiosis.htm
http://www .accessexcellence.org/RC/VL/GG/meiosis. php
http://www2.estrellamountain.edu/faculty/farabee/biobk/biobook
meiosis. html
http://www2.estrellamountain.edu/faculty/farabee/biobk/biobook
meiosis. html
http://biology.clc.uc.edu/courses/bio 104/meiosis. htm
http://biology.about.com/library/weekly/aa092800a.htm
http://www.brown.edu/Courses/BI0032/gentherp/phaseIB1.html