Download cell division: binary fission and mitosis

binary fission
A method of asexual reproduction that is employed by most
prokaryotes. In binary fission, the living cell divides into two
equal, or nearly equal, parts. It begins when the DNA of the cell is
replicated. Each circular strand of DNA then attaches to the
plasma membrane. The cell elongates, causing the two
chromosomes to separate. The plasma membrane then invaginates
(grows inward) and splits the cell into two daughter cells through
a process called cytokinesis.
Binary fission theoretically results in two identical cells.
However, the DNA of bacteria has a relatively high mutation rate.
This rapid rate of genetic change is what makes bacteria capable
of developing resistance to antibiotics and helps them exploit
invasion into a wide range of environments.
A bacterial cell reproducing by
binary fission. The two resultant
daughter cells are genetically
identical. (Photo: Dr. Vincent A.
Fischetti, Laboratory of Bacterial
Pathogenesis and Immunology,
Rockefeller University)
Similar to more complex organisms, bacteria also have
mechanisms for exchanging genetic material. Although not equivalent to sexual reproduction,
the end result is that a bacterium contains a combination of traits from two different parental
cells. Three different modes of exchange have thus far been identified in bacteria. (See gene
transfer.)
Conjunction involves the direct joining of two bacteria, which allows their circular DNAs to
undergo recombination. Bacteria can also undergo transformation by absorbing remnants of
DNA from dead bacteria and integrating these fragments into their own DNA. Lastly, bacteria
can exchange genetic material through a process called transduction, in which genes are
transported into and out of the cell by bacterial viruses, called bacteriophages, or by plasmids, an
autonomous self-replicating extrachromosomal circular DNA.
Related categories
• MICROBIOLOGY
• CELL BIOLOGY
Also on this site:
Encyclopedia of Alternative Energy & Sustainable Living
Encyclopedia of History
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http://www.daviddarling.info/encyclopedia/B/binary_fission.html
CELL DIVISION: BINARY FISSION AND MITOSIS
Table of Contents
The Cell Cycle | Prokaryotic Cell Division | Eukaryotic Cell Division | Mitosis
Prophase | Metaphase | Anaphase | Telophase | Cytokinesis | Links
The Cell Cycle | Back to Top
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.
Cytokinesis is the process where one cell splits off from its sister cell. It usually
occurs after cell division. The Cell Cycle is the sequence of growth, DNA replication,
growth and cell division that all cells go through. Beginning after cytokinesis, the
daughter cells are quite small and low on ATP. They acquire ATP and increase in size
during the G1 phase of Interphase. Most cells are observed in Interphase, the longest
part of the cell cycle. After acquiring sufficient size and ATP, the cells then undergo
DNA Synthesis (replication of the original DNA molecules, making identical copies,
one "new molecule" eventually destined for each new cell) which occurs during the S
phase. Since the formation of new DNA is an energy draining process, the cell
undergoes a second growth and energy acquisition stage, the G2 phase. The energy
acquired during G2 is used in cell division (in this case mitosis).
The cell cycle. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer
Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
Regulation of the cell cycle is accomplished in several ways. Some cells divide
rapidly (beans, for example take 19 hours for the complete cycle; red blood cells must
divide at a rate of 2.5 million per second). 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 (for restriction).
Prokaryotic Cell Division | Back to Top
Prokaryotes are much simpler in their organization than are eukaryotes. There are a
great many more organelles in eukaryotes, also more chromosomes. The usual method
of prokaryote cell division is termed binary fission. The prokaryotic chromosome is a
single DNA molecule that first replicates, then attaches each copy to a different part
of the cell membrane. When the cell begins to pull apart, the replicate and original
chromosomes are separated. Following cell splitting (cytokinesis), there are then two
cells of identical genetic composition (except for the rare chance of a spontaneous
mutation).
This animated GIF of binary fission is from:
http://www.slic2.wsu.edu:82/hurlbert/micro101/pages/Chap2.html#two_bact_groups
The prokaryote chromosome is much easier to manipulate than the eukaryotic one.
We thus know much more about the location of genes and their control in
prokaryotes.
One consequence of this asexual method of reproduction is that all organisms in a
colony are genetic equals. When treating a bacterial disease, a drug that kills one
bacteria (of a specific type) will also kill all other members of that clone (colony) it
comes in contact with.
Rod-Shaped Bacterium, E. coli, dividing by binary fission (TEM x92,750). This image
is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission.
Rod-Shaped Bacterium, hemorrhagic E. coli, strain 0157:H7 (division) (SEM x22,810).
This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission.
Eukaryotic Cell Division | Back to Top
Due to their increased numbers of chromosomes, organelles and complexity,
eukaryote cell division is more complicated, although the same processes of
replication, segregation, and cytokinesis still occur.
Mitosis | Back to Top
Mitosis is the process of forming (generally) identical daughter cells by replicating
and dividing the original chromosomes, in effect making a cellular xerox. Commonly
the two processes of cell division are confused. Mitosis deals only with the
segregation of the chromosomes and organelles into daughter cells.
Click here to view an animated GIF of mitosis from
http://www.biology.uc.edu/vgenetic/mitosis/mitosis.htm.
Eukaryotic chromosomes occur in the cell in greater numbers than prokaryotic
chromosomes. The condensed replicated chromosomes have several points of interest.
The kinetochore is the point where microtubules of the spindle apparatus attach.
Replicated chromosomes consist of two molecules of DNA (along with their
associated histone proteins) known as chromatids. The area where both chromatids are
in contact with each other is known as the centromere the kinetochores are on the
outer sides of the centromere. Remember that chromosomes are condensed chromatin
(DNA plus histone proteins).
Structure of a eukaryotic chromosome. Image from Purves et al., Life: The Science of
Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman
(www.whfreeman.com), used with permission.
During mitosis replicated chromosomes are positioned near the middle of the
cytoplasm and then segregated so that each daughter cell receives a copy of the
original DNA (if you start with 46 in the parent cell, you should end up with 46
chromosomes in each daughter cell). To do this cells utilize microtubules (referred to
as the spindle apparatus) to "pull" chromosomes into each "cell". The microtubules
have the 9+2 arrangement discussed earlier. Animal cells (except for a group of
worms known as nematodes) have a centriole. Plants and most other eukaryotic
organisms lack centrioles. Prokaryotes, of course, lack spindles and centrioles; the cell
membrane assumes this function when it pulls the by-then replicated chromosomes
apart during binary fission. Cells that contain centrioles also have a series of smaller
microtubules, the aster, that extend from the centrioles to the cell membrane. The aster
is thought to serve as a brace for the functioning of the spindle fibers.
Structure and main features of a spindle apparatus. Image from Purves et al., Life: The
Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman
(www.whfreeman.com), used with permission.
The phases of mitosis are sometimes difficult to separate. Remember that the process
is a dynamic one, not the static process displayed of necessity in a textbook.
Prophase | Back to Top
Prophase is the first stage of mitosis proper. Chromatin condenses (remember that
chromatin/DNA replicate during Interphase), the nuclear envelope dissolves,
centrioles (if present) divide and migrate, kinetochores and kinetochore fibers form,
and the spindle forms.
Pea Plant Nuclear DNA, from Vicea faba (TEM x105,000). This image is copyright
Dennis Kunkel at www.DennisKunkel.com, used with permission.
The events of Prophase. Image from Purves et al., Life: The Science of Biology, 4th Edition,
by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with
permission.
Metaphase | Back to Top
Metaphase follows Prophase. The chromosomes (which at this point consist of
chromatids held together by a centromere) migrate to the equator of the spindle, where
the spindles attach to the kinetochore fibers.
Anaphase | Back to Top
Anaphase begins with the separation of the centromeres, and the pulling of
chromosomes (we call them chromosomes after the centromeres are separated) to
opposite poles of the spindle.
The events of Metaphase and Anaphase. Image from Purves et al., Life: The Science of
Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman
(www.whfreeman.com), used with permission.
Telophase | Back to Top
Telophase is when the chromosomes reach the poles of their respective spindles, the
nuclear envelope reforms, chromosomes uncoil into chromatin form, and the
nucleolus (which had disappeared during Prophase) reform. Where there was one cell
there are now two smaller cells each with exactly the same genetic information. These
cells may then develop into different adult forms via the processes of development.
The events of Telophase. Image from Purves et al., Life: The Science of Biology, 4th Edition,
by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with
permission.
Cytokinesis | Back to Top
Cytokinesis is the process of splitting the daughter cells apart. Whereas mitosis is the
division of the nucleus, cytokinesis is the splitting of the cytoplasm and allocation of
the golgi, plastids and cytoplasm into each new cell.
Links | Back to Top
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Access Excellence page on Mitosis
Cell Division and the Cell Cycle (University of Alberta): Similar to this page, but with its own
glossary and questions.
Amoeba Proteus Mitosis Small photomicrographs of protistan mitosis.
Cell Reproduction Notes from University of Georgia, plus some cool graphics of mitosis.
Phases of Mitosis U Texas QuickTime® movies of mitosis.
Animated Mitosis Yale University, a simplified series of cartoons about mitosis.
Mitosis U Southern Mississippi, Grayscale drawings and photomicrographs of mitosis stages.
Mitosis San Diego State U, shocked animation of the process. You will need the Shockwave
plugin to view. If you don't have it, you can download it from them.
McGill University Mitosis Page Quality site, with photos and downloadable animation and video.
Comparison of Mitosis and Meiosis Whitman College, table summarizing each process.
Whitefish Mitosis Review Cornell, photomicrographs of mitosis in whitefish. A nice review after
lab! Part of a more extensive page of Cell Division Tutorials.
Virtual Mitosis University of Cincinnati, Animated GIF and text about the stages of mitosis.
Text ©1992, 1994, 1997, 1998, 2000, 2001, by M.J. Farabee, all rights reserved. Use for educational
purposes is encouraged.
Back to Table of Contents | MEIOSIS AND SEXUAL REPRODUCTION
Email: [email protected]
Last modified: Tuesday May 18 2010
The URL of this page is: www.emc.maricopa.edu/faculty/farabee/biobk/biobookmito.html
JavaScript is required to properly view this page. Please enable JavaScript.
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What is Biology?
How can there be seedless grapes, and how do they reproduce? Why is carbon monoxide
extremely poisonous? Why can’t you tickle yourself? What causes the smell after rain?
How do vitamins work? What's all this fuss about stem cells? What makes us yawn? Why
are frogs growing extra legs out of their legs? Which came first, the chicken or the egg?
Biology is the study of living things and their vital processes. Because biology covers such a
broad area, it has been traditional to separate the study of plants (botany) from that of animals
(zoology), and the study of structure of organisms (morphology) from that of function
(physiology). Despite their apparent differences, all the subdivisions are interrelated by basic
principles, so current practice tends to investigate those biological phenomena that all living
things have in common. The advancement of knowledge and technology has resulted in further
categorizations that include, but are far from restricted to: cell biology, population biology,
ecology, genetics, biochemistry, molecular biology, microbiology, and physical anthropology.
The number of different animal and plant species on earth is estimated at between 2 million and
4.5 million. We are presently killing off species through human action at a faster rate than at any
other time, but we are also discovering new oceanic species at an increasing rate.
It is not known when the study of biology originated, but it can be safely assumed that early
humanoids had some experimental knowledge of the animals and plants around them. One's very
survival relied on the recognition of poisonous plants and on the basic understanding of the
habits of predators. Many of the earliest records of biology come from the bas-reliefs left behind
by the Assyrians and Babylonians. Papyrus and artifacts found in tombs and pyramids indicate
that the Egyptians possessed considerable, albeit archaic by today's standards, medical
knowledge. There is growing evidence from China and India as early as 2500 BC that there were
general practices of therapeutic healing, silkworm use to produce silk, biological control of crops
,and agricultural cultivation.
With the arrival of Greek civilization, the study of biology shifted dramatically to a belief that
every event has a cause and that a particular cause produces a particular effect. These
philosophers of science assumed the existence of a natural law governing the universe; a law that
can be comprehended by man through his use of observation and deduction. Although they
established the science of biology, their greatest contribution to science was the idea of rational
thought.
Skipping forward through the rapid evolution of biological advancements to today, recent
discoveries concerning hereditary mechanisms and genetic engineering have raised ethical issues
beyond our previous imagination, and have potential ramifications that could affect the very
existence of life itself. It will be interesting to see what is to come in the future!
With over 7 billion humans on Earth today, and growing explosively. We are rapidly stretching
the limits of our planet to sustain life as we know it. Global warming, depleted food sources,
desertification, weather pattern changes, shrinking ozone layers, and rising ocean levels are
warning signs of these stresses.
This is where you can get involved! Whether you enter the doors of biological science or sit on
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support or be critics. Become informed!
Biology Courses are currently offered at Kwantlen on the Surrey, Langley and Richmond
Campuses. Check out these offerings in the Calendar. If you need science or Q credits for your
non-science degree, have a look at our Biology Today (BIOL 1112) course. It’s interesting and it
will inform you on the most recent contemporary biological topics in the news.
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What is Microbiology?
Microbiology is the study of small living things. Generally this means living things that are too
small to see without the use of a microscope. These life forms are called microorganisms or
microbes. Microorganisms include bacteria, archaea (a type of prokaryote a bit like bacteria but
they have a distinct evolutionary origin), viruses, protozoa (single-cell eukaryotes like amoeba),
microscopic fungi and yeasts, and microscopic algae (plant-like organisms). Microorganisms
were discovered over three hundred years ago and it is thought that many new microbes have yet
to be discovered. Microbiology is a wide area of science that includes bacteriology, virology,
mycology, phycology, parasitology, and other branches of biology.
Most living things can be classified into prokaryotes or eukaryotes depending on whether their
nuclear material (for example DNA) is surrounded by a membrane or not. Archaea and bacteria
are prokaryotes. Most animals (including humans) and plants are eukaryotes. Protozoa, fungi,
yeasts, and algae are eukaryotes. Viruses are a little different. Traditional classification systems
do not classify viruses as living organisms. However in practise they are considered
microorganisms. The study of viruses is called virology.
Microbiology therefore includes the study of both prokaryotic and eukaryotic microorganisms. In
practise the majority of microbiology is concerned with bacteria and/or viruses although
eukaryotic microbiology is also a very important branch of microbiology. Many diseases of
animals (including humans) and plants are caused by bacteria, viruses, amoeba, and fungi.
Bacteria are important in probiotics, they are used in food production (e.g. yoghurt and cheese)
and biotechnology. Yeasts and fungi are important in food and drink production (e.g. wine, beer,
bread) and are also used to produce important pharmaceuticals (e.g. antibiotics).
Microbiology science resource at Microbiology. Probiotics science resource at Probiotics and
current topics on microbiology research at the Microbiology Blog
Microbiology Articles
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home | microbiology | probiotics | plasmids | bacteria | amoeba |