2.5: Cell Divison
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Define mitosis and cytokinesis.
Miitosis is a process during cell division in which the cell nucleus divides into two. Cytokinesis is the division of the cell's cytoplasm following the division of the nucleus.
Outline each stage of the cell cycle using the diagram.
- Stage G1: Cell grows in preperation for mitosis, e.g. producing proteins, cytoplasmic organelles (mitochondria, ER) Growth stage 1.
- Stage S: DNA synthesis with chromosomes replicated.
- Stage G2: completes preperation for mitosis. Growth stage 2.
- Mitosis: nuclear division in four phases: prophase, metaphase, anaphase, telophase.
- Cytokinesis: occurs after mitosis and is the division of the cytoplasm and the cell into two.
Define tumour and distinguish between a benign tumour and a malignant tumour.
A tumour is a mass of cells caused by uncontrolled cell division. Tumours can occur in any organ or tissue. If they are benign the mass stays at the original site. In a malignant tumour, cells detach and spread and impair other organs and tissues.
Outline a cause of tumour growth.
Cells that do not follow the normal regulatory signals for the cell cycle and do not stop dividing become tumour (cancer) cells, e.g. a mutation in the proto-oncogenes leads to uncontrolled cell division.
Interphase is a long phase, e.g. it can be 90% cell cycle and is divided into G1, S and G2 stages. In the growth stages it involves protein synthesis and the increase in number of organelles ini preperation for cell division, e.g. increased number of mitochondria and/or chloroplasts. The S stage of interphase involves DNA replication. It is a very active time in a cell when many metabolic reactions occur (interphase is sometimes miscalled the 'resting stage').
Describe the phases of mitosis.
- Prophase - Chromosomes become visible as long thing threads, DNA twists and curls forming thicker and shorter supercoils to become two chromatids joined at the centromere. Nuclear membrane disappears and a spindle forms.
- Metaphase - Chromatids line up at the equator of the cell and centre of spindle. Centromere is attached to spindle microtubules. Supercoiling is at maximum.
- Anaphase - Centromere splits. Spindle fibres shorten pulling the two chromatids apart taking each to opposite poles of the cell.
- Telophase - Chromosomes at each pole and nuclear membrane forms around each cluster. Spindle fibres disappear. At the end of telophase, cytokinesis occurs and two smaller daughter cells are formed.
Describe the product of mitosis.
Mitosis produces two identical daughter nuclei. THey have the same genetic information as the parent nuclei due to DNA replication during the S stage of interphase. The two sister chromatids separate during anaphase and move to opposite poles.
Outline the importance of mitosis as a biological process.
Mitosis is a vitally important process involved in growth repair and maintenance of cells and tissues. After a zygote has formed, growth and development depend on mitosis to produce new cells. It is also important in asexual reproduction as it lead to the formation of two identical daughter cells.
Outline cell division and growth.
- 1. Mature parent cell.
- 2. Process is mitosis.
- 3. 2 small daughter cells
- 4. Process is increase in size
- 5. Mature cell.
Discuss the importance of supercoiling during mitosis.
Supercoiling involves the DNA of chromosomes condensing into long regular supercoils under the influence of the protein condensin. The supercoiling is at a maximum at metaphase when the sister chromatids are aligned on the spindle. The highly condensed form has greater mechanical strength to withstand the force of the mitotic spindle and segregation to daughter cells.
Outline two differences between mitosis in plants and animals.
During mitosis in plant cells, vesicles form Golgi apparatus fuse at the equator to form a cell plate which will become the cell wall. This does not happen in animal cells. Animal cells the spindle fibres begin to form around the two centrioles. Plant cells do not have centrioles.
Compare cell division in prokaryotic and eukaryotic cells.
Cell division in eukaryotic cells involves mitosis and cytokinesis. In prokaryotic cells, the circular chromosome replicates in DNA synthesis and the cell pinches into two daughter cells in a process called binary fission.
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