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In the simplest manner, we are just a bundle of cells, trillions of cells. But we all came about from the joining of only two from our parents. The math proves how rapid this process is, but rapid does not necessarily mean quick and simple.
As you will learn, this is a very complicated process, and a very important one... |
"These facts shaw that mitosis is due to the co-ordinate play of an extremely complex system of forces which are as yet scarcely comprehended. Its purpose is, however, as obvious as its physiological explanation is difficult. It is the end of mitosis to divide every part of the chromatin of the mother-cell equally between the daughter-nuclei. All the other operations are tributary to this. We may therefore regard the mitotic figure as essentially an apparatus for the distribution of the hereditary substance, and in this sense as the especial instrument of inheritance."
Edmund Beecher Wilson, The Cell in Development and Inheritance (1896)
Mitosis is part of the cycle of cell division. The chromosomes of a cell are copied to make two identical sets of chromosomes, and the cell nucleus divides into two identical nuclei.
Before mitosis, the cell creates an identical set of its own genetic information – this is called DNA replication. The genetic information is in the DNA of the chromosomes. At the beginning of mitosis the chromosomes wind up into visible objects that can be seen with a light microscope. The chromosomes are now two chromatids joined at the centromere. Since the two chromatids are identical to each other, they are called sister chromatids.
Mitosis happens in all types of dividing cells in the human body except with sperm and ova. The sperm and ova are gametes or sex cells. The gametes are produced by a different division method called meiosis.
There are five phases of mitosis. Each phase is used to describe what kind of change the cell is going through. The phases are prophase, prometaphase, metaphase, anaphase and telophase.
Before mitosis, the cell creates an identical set of its own genetic information – this is called DNA replication. The genetic information is in the DNA of the chromosomes. At the beginning of mitosis the chromosomes wind up into visible objects that can be seen with a light microscope. The chromosomes are now two chromatids joined at the centromere. Since the two chromatids are identical to each other, they are called sister chromatids.
Mitosis happens in all types of dividing cells in the human body except with sperm and ova. The sperm and ova are gametes or sex cells. The gametes are produced by a different division method called meiosis.
There are five phases of mitosis. Each phase is used to describe what kind of change the cell is going through. The phases are prophase, prometaphase, metaphase, anaphase and telophase.
Prophase
During prophase (Greek for “before stage”), chromatin in the nucleus condense to form chromosomes. Pairs of these move to opposite sides of the nucleus in preparation of cell division.
Prometaphase
During prometaphase, the nuclear envelope around the chromosomes breaks down. Now there is no nucleus and the sister chromatids are free. A protein called a kinetochore forms at each centromere. Long thin proteins reach across from opposite poles of the cell and attach to each kinetochore.
Metaphase
During metaphase, the sister chromatids are aligned by the pushing and pulling of the attached kinetochore microtubules, similar to a game of "tug of war". Both sister chromatids stay attached to each other at the centromere. The chromosomes line up on the cell's equator, or center line, and are prepared for division.
During prophase (Greek for “before stage”), chromatin in the nucleus condense to form chromosomes. Pairs of these move to opposite sides of the nucleus in preparation of cell division.
Prometaphase
During prometaphase, the nuclear envelope around the chromosomes breaks down. Now there is no nucleus and the sister chromatids are free. A protein called a kinetochore forms at each centromere. Long thin proteins reach across from opposite poles of the cell and attach to each kinetochore.
Metaphase
During metaphase, the sister chromatids are aligned by the pushing and pulling of the attached kinetochore microtubules, similar to a game of "tug of war". Both sister chromatids stay attached to each other at the centromere. The chromosomes line up on the cell's equator, or center line, and are prepared for division.
Anaphase
During anaphase, the sister chromatids split apart and move from the cell's equator (metaphase plate) to the poles of the cell. The kinetochore is attached to the centromere. The microtubules hold on to kinetochore and shorten in length. Another group of microtubules, the non-kinetochore microtubules, do the opposite. They become longer. The cell begins to stretch out as the opposite ends are pushed apart.
Telophase
Telophase is the final stage in mitosis: the cell itself is ready to divide. One set of chromosomes is now at each pole of the cell. Each set is identical. The spindle fibers begin to disappear, and a nuclear membrane forms around each set of chromosomes. Also a nucleolus appears within each new nucleus and single stranded chromosomes uncoil into invisible strands of chromatin.
Cytokinesis
Although it is not considered a stage of mitosis, cytokinesis, is very important to cell division. During cytokinesis, the cell physically splits. This occurs just after anaphase and during telophase. The cleavage furrow, which is the pinch caused by the ring of proteins, pinches off completely, closing off the cell.
The cell now has reproduced itself successfully. After cytokinesis, the cell goes back into interphase, where the cycle is repeated. If cytokinesis were to occur to a cell that had not gone through mitosis, then the daughter cells would be different or not function properly. One would still have the nucleus and the other would lack a nucleus. Cytokinesis is different in both animals and plant cells. In plant cells, instead of splitting into two halves, it forms a cell plate.
During anaphase, the sister chromatids split apart and move from the cell's equator (metaphase plate) to the poles of the cell. The kinetochore is attached to the centromere. The microtubules hold on to kinetochore and shorten in length. Another group of microtubules, the non-kinetochore microtubules, do the opposite. They become longer. The cell begins to stretch out as the opposite ends are pushed apart.
Telophase
Telophase is the final stage in mitosis: the cell itself is ready to divide. One set of chromosomes is now at each pole of the cell. Each set is identical. The spindle fibers begin to disappear, and a nuclear membrane forms around each set of chromosomes. Also a nucleolus appears within each new nucleus and single stranded chromosomes uncoil into invisible strands of chromatin.
Cytokinesis
Although it is not considered a stage of mitosis, cytokinesis, is very important to cell division. During cytokinesis, the cell physically splits. This occurs just after anaphase and during telophase. The cleavage furrow, which is the pinch caused by the ring of proteins, pinches off completely, closing off the cell.
The cell now has reproduced itself successfully. After cytokinesis, the cell goes back into interphase, where the cycle is repeated. If cytokinesis were to occur to a cell that had not gone through mitosis, then the daughter cells would be different or not function properly. One would still have the nucleus and the other would lack a nucleus. Cytokinesis is different in both animals and plant cells. In plant cells, instead of splitting into two halves, it forms a cell plate.
Applications in Molecular Cloning
Molecular cloning is the process of cutting out a human gene and putting it into a piece of bacterial DNA. Mitosis is the process in which a cell divides into two cells that each has the same amount of DNA as the original cell. There are some similarities between molecular cloning and mitosis, but the differences outnumber the commonalities. This is because molecular cloning is an experimental technique done by researchers and doesn’t happen in the natural world. Molecular cloning transfers one gene from the cell of one organism to the cell of another. Mitosis copies all genes in a cell and splits the genes evenly between two cells of the same organism.
Both molecular cloning and mitosis involve the transfer of genetic information from one cell to another cell. Both processes require the help of enzymes, the protein machines that break and build DNA. These enzymes naturally exist in cells and do not have to be invented by a researcher. The process of cutting and pasting DNA in molecular cloning and the process of copying DNA for mitosis both require an enzyme called DNA ligase. This enzyme connects smaller pieces of DNA into one long piece of DNA. It is necessary for copying all genes in a cell or just connecting a human gene that has been inserted into bacterial DNA. Lastly, both molecular cloning and mitosis require that the nuclear envelope that houses DNA be broken to pieces, so that the DNA can be manipulated.
One of the major differences between molecular cloning and mitosis is that cloning results in recombinant DNA, which is hybrid DNA from two different organisms. Furthermore, mitosis cannot cut and paste a gene from one piece of DNA to another piece of DNA, even within the same organism. Thus, only molecular cloning can create fusion proteins that are part human and part jellyfish, for example, which are stored in a bacterial cell. Another major difference is that in mitosis, the original piece of DNA is kept intact after it is copied. In molecular cloning, a human gene is cut out from a human cell and inserted into a piece of bacteria DNA that is then placed into a bacteria cell.
Applications in Tissue Culture
Plant research often involves growing new plants in a controlled environment. These may be plants that we have genetically altered in some way or may be plants of which we need many copies all exactly alike. These things can be accomplished through tissue culture of small tissue pieces from the plant of interest. These small pieces may come from a single mother plant or they may be the result of genetic transformation of single plant cells which are then encouraged to grow and to ultimately develop into a whole plant. Tissue culture techniques are often used for commercial production of plants as well as for plant research.
Tissue culture involves the use of small pieces of plant tissue (explants) which are cultured in a nutrient medium under sterile conditions. Using the appropriate growing conditions for each explant type, plants can be induced to rapidly produce new shoots, and, with the addition of suitable hormones new roots. These plantlets can also be divided, usually at the shoot stage, to produce large numbers of new plantlets. The new plants can then be placed in soil and grown in the normal manner.
Molecular cloning is the process of cutting out a human gene and putting it into a piece of bacterial DNA. Mitosis is the process in which a cell divides into two cells that each has the same amount of DNA as the original cell. There are some similarities between molecular cloning and mitosis, but the differences outnumber the commonalities. This is because molecular cloning is an experimental technique done by researchers and doesn’t happen in the natural world. Molecular cloning transfers one gene from the cell of one organism to the cell of another. Mitosis copies all genes in a cell and splits the genes evenly between two cells of the same organism.
Both molecular cloning and mitosis involve the transfer of genetic information from one cell to another cell. Both processes require the help of enzymes, the protein machines that break and build DNA. These enzymes naturally exist in cells and do not have to be invented by a researcher. The process of cutting and pasting DNA in molecular cloning and the process of copying DNA for mitosis both require an enzyme called DNA ligase. This enzyme connects smaller pieces of DNA into one long piece of DNA. It is necessary for copying all genes in a cell or just connecting a human gene that has been inserted into bacterial DNA. Lastly, both molecular cloning and mitosis require that the nuclear envelope that houses DNA be broken to pieces, so that the DNA can be manipulated.
One of the major differences between molecular cloning and mitosis is that cloning results in recombinant DNA, which is hybrid DNA from two different organisms. Furthermore, mitosis cannot cut and paste a gene from one piece of DNA to another piece of DNA, even within the same organism. Thus, only molecular cloning can create fusion proteins that are part human and part jellyfish, for example, which are stored in a bacterial cell. Another major difference is that in mitosis, the original piece of DNA is kept intact after it is copied. In molecular cloning, a human gene is cut out from a human cell and inserted into a piece of bacteria DNA that is then placed into a bacteria cell.
Applications in Tissue Culture
Plant research often involves growing new plants in a controlled environment. These may be plants that we have genetically altered in some way or may be plants of which we need many copies all exactly alike. These things can be accomplished through tissue culture of small tissue pieces from the plant of interest. These small pieces may come from a single mother plant or they may be the result of genetic transformation of single plant cells which are then encouraged to grow and to ultimately develop into a whole plant. Tissue culture techniques are often used for commercial production of plants as well as for plant research.
Tissue culture involves the use of small pieces of plant tissue (explants) which are cultured in a nutrient medium under sterile conditions. Using the appropriate growing conditions for each explant type, plants can be induced to rapidly produce new shoots, and, with the addition of suitable hormones new roots. These plantlets can also be divided, usually at the shoot stage, to produce large numbers of new plantlets. The new plants can then be placed in soil and grown in the normal manner.
Ponder this
Considering that plant cells have thick, tough cell walls made from cellulose, how would a plant cell replicate?
What about that rigid parts of the human body such as bones and teeth. Considering how we develop from a continuous series of cell replication and specialisation, how did these parts develop and grow?
Discuss
It has been said that our whole body regenerates every seven years as cells die and new ones replace them. But this process does not apply at the same rate everywhere. Our stomach lining is renewed daily, but our blood cells are replaced every three months. Why is this? What governs this process? Can we tweak this process (speed it up, or slow it down) to benefit our health?
It has been said that our whole body regenerates every seven years as cells die and new ones replace them. But this process does not apply at the same rate everywhere. Our stomach lining is renewed daily, but our blood cells are replaced every three months. Why is this? What governs this process? Can we tweak this process (speed it up, or slow it down) to benefit our health?
Further readings
Mitosis, for a more comprehensive and detailed explanation of the process.
Molecular cloning, an experimental method used in molecular biology that uses mitosis in replicating recombinant DNAs.
Cell culture, which uses mitosis to artificially mass produce cells and tissues.
"Artificial chicken grown from cells gets a taste test", thanks to mitosis, vegetarians have a new source of protein.
