Diagram showing the four stages of mitosis. Once interphase has been completed (the main part of the cell cycle which prepares the cell for dividing) mitosis starts. The first phase is prophase, here the replicated chromosomes condense (become shorter and thicker and visible with a microscope). During metaphase the chromosomes align at the equator of the cell and attach to the mitotic spindle at their centromeres. Chromosomes do not align in homologous pairs. During anaphase the spindle contracts causing the centromeres to split apart and the chromtids to be pulled to either pole of the cell. During telophase the chromatids (now called chromosomes again) elongate; the nuclear envelopes also form making two new nuclei. This is mitosis complete. The cell then divides into two through a process called cytokinesis where the cytoplasm pinches in and meets at the middle.
Exam 2: Cell division
Cell division by mitosis leads to production of two daughter cells that are genetically identical to the parent cell. Dividing cells undergo a regular pattern of events known as the cell cycle. The cell cycle is a continuous process but for convenience of description it is subdivided into three main processes: interphase, mitosis and cytokinesis. Interphase is a very important and highly metabolically active stage of the cell cycle where the DNA replicates and organelles are replicated. Once interphase is complete, mitosis occurs leading to division of the DNA to either pole of the cell. Lastly, cytokinesis occurs whereby the cell splits down the middle leading to the formation of two new daughter cells.
Interphase
This is the longest part of the cell cycle during which a cell increases in size and produces organelles which will be divided between the two new daughter cells. The amount of DNA is doubled during this period. Just before the next cell division the chromosomes replicate so that each then consists of two chromatids joined together by the centromere. There is considerable metabolic activity as these processes need energy in the form of ATP. The chromosomes are not visible at interphase because the chromosome material, chromatin, is dispersed throughout the nucleus. It is only during the first phase of mitosis, called prophase, that the chromosomes start to condense and become visible.
Mitosis
Prophase
During prophase the following changes take place:
1. The chromosomes condense (shorten and become thicker) and become visible as long thin threads. The chromosomes are now referred to as pairs of chromatids which are joined at a centromere.
2. In animal cells (and cells of lower plants), the centrioles, which have divided, move to the opposite poles of the cells.
3. Protein micro-tubules form from each centriole and the mitotic spindle develops, extending from pole to pole.
4. Towards the end of prophase the nuclear membrane disintegrates and the nucleolus disappears.
5. Pairs of chromatids can clearly be seen lying free in the cytoplasm.
Metaphase
During Metaphase the chromosomes arrange themselves at the centre or equator of the spindle and become attached to certain spindle fibres at their centromere. Contraction of the micro-tubule spindle fibres draws the individual chromatids slightly apart.
Anaphase
Anaphase is a very rapid stage. The centromere splits and the spindle fibres contract and pull the now separated chromatids to the poles, centromere first.
Telophase
Telophase is the final stage of mitosis. The chromosomes have now reached the poles of the cell and are referred to as chromosomes again. They uncoil and lengthen. The spindle breaks down, the centrioles replicate, the nucleous reappears and the nuclear membrane reforms. In animal cells cytokinesis occurs by the constriction of the centre of the parent cell from the outside inwards. In plant cells, a cell plate forms across the equator of the parent cell from the centre outwards and a new cell wall is laid down.
BY1: Significance of mitosis
Mitosis produces two cells that have the same number of chromosomes as the parent cell (haploid) and each chromosome is genetically identical to it's original parent cell chromosome. Therefore the division allows the production of cells that are genetically identical to the parent and so gives genetic stability.
By producing new cells, mitosis leads to growth of an organism and also allows for repair of tissues and the replacement of dead cells. An example of mitosis in plants is in the root tip. In human skin, dead surface cells are replaced by identical cells from below.
Asexual reproduction results in complete offspring that are identical to the parent. Asexual reproduction involving mitosis takes place in certain flowering plants where organs such as bulbs, tubers and runners produce large numbers of identical offspring in a relatively short period of time. There is no genetic variation between each individual. However, most of these plants also reproduce sexually.
Asexual reproduction also takes place in unicellular organisms such as yeast and bacteria. However these do not involve mitosis as described above.
Yeast cells replicate asexually through budding (where a small bud forms on the side of the parent cell. This then develops and gets bigger until it is similar in size and shape to the parent cell. It now buds off from the parent cell and is released)
Bacterial cells replicate through binary fission (where the DNA loose in the cytoplasm [nucleoid] replicates and the parent cell then splits into two new bacterial cells each with the same DNA as the original bacterial cell)
Cell division by mitosis leads to production of two daughter cells that are genetically identical to the parent cell. Dividing cells undergo a regular pattern of events known as the cell cycle. The cell cycle is a continuous process but for convenience of description it is subdivided into three main processes: interphase, mitosis and cytokinesis. Interphase is a very important and highly metabolically active stage of the cell cycle where the DNA replicates and organelles are replicated. Once interphase is complete, mitosis occurs leading to division of the DNA to either pole of the cell. Lastly, cytokinesis occurs whereby the cell splits down the middle leading to the formation of two new daughter cells.
Interphase
This is the longest part of the cell cycle during which a cell increases in size and produces organelles which will be divided between the two new daughter cells. The amount of DNA is doubled during this period. Just before the next cell division the chromosomes replicate so that each then consists of two chromatids joined together by the centromere. There is considerable metabolic activity as these processes need energy in the form of ATP. The chromosomes are not visible at interphase because the chromosome material, chromatin, is dispersed throughout the nucleus. It is only during the first phase of mitosis, called prophase, that the chromosomes start to condense and become visible.
Mitosis
Prophase
During prophase the following changes take place:
1. The chromosomes condense (shorten and become thicker) and become visible as long thin threads. The chromosomes are now referred to as pairs of chromatids which are joined at a centromere.
2. In animal cells (and cells of lower plants), the centrioles, which have divided, move to the opposite poles of the cells.
3. Protein micro-tubules form from each centriole and the mitotic spindle develops, extending from pole to pole.
4. Towards the end of prophase the nuclear membrane disintegrates and the nucleolus disappears.
5. Pairs of chromatids can clearly be seen lying free in the cytoplasm.
Metaphase
During Metaphase the chromosomes arrange themselves at the centre or equator of the spindle and become attached to certain spindle fibres at their centromere. Contraction of the micro-tubule spindle fibres draws the individual chromatids slightly apart.
Anaphase
Anaphase is a very rapid stage. The centromere splits and the spindle fibres contract and pull the now separated chromatids to the poles, centromere first.
Telophase
Telophase is the final stage of mitosis. The chromosomes have now reached the poles of the cell and are referred to as chromosomes again. They uncoil and lengthen. The spindle breaks down, the centrioles replicate, the nucleous reappears and the nuclear membrane reforms. In animal cells cytokinesis occurs by the constriction of the centre of the parent cell from the outside inwards. In plant cells, a cell plate forms across the equator of the parent cell from the centre outwards and a new cell wall is laid down.
BY1: Significance of mitosis
Mitosis produces two cells that have the same number of chromosomes as the parent cell (haploid) and each chromosome is genetically identical to it's original parent cell chromosome. Therefore the division allows the production of cells that are genetically identical to the parent and so gives genetic stability.
By producing new cells, mitosis leads to growth of an organism and also allows for repair of tissues and the replacement of dead cells. An example of mitosis in plants is in the root tip. In human skin, dead surface cells are replaced by identical cells from below.
Asexual reproduction results in complete offspring that are identical to the parent. Asexual reproduction involving mitosis takes place in certain flowering plants where organs such as bulbs, tubers and runners produce large numbers of identical offspring in a relatively short period of time. There is no genetic variation between each individual. However, most of these plants also reproduce sexually.
Asexual reproduction also takes place in unicellular organisms such as yeast and bacteria. However these do not involve mitosis as described above.
Yeast cells replicate asexually through budding (where a small bud forms on the side of the parent cell. This then develops and gets bigger until it is similar in size and shape to the parent cell. It now buds off from the parent cell and is released)
Bacterial cells replicate through binary fission (where the DNA loose in the cytoplasm [nucleoid] replicates and the parent cell then splits into two new bacterial cells each with the same DNA as the original bacterial cell)
Make a list of the key words and give their definitions. e.g. homologous means that in the diploid cell each chromosome has a partner of exactly the same length and with precisely the same genes.
Construct a table summarising the changes that take place at each of the four stages of mitosis.
Construct a pie chart showing the relative length of time of each period of the cell cycle.
Draw labelled diagrams showing the stages in mitosis.
Construct a table summarising the changes that take place at each of the four stages of mitosis.
Construct a pie chart showing the relative length of time of each period of the cell cycle.
Draw labelled diagrams showing the stages in mitosis.