Cell division→ CELL CYCLE, MITOSIS The necessity for cell division in living organisms. Most of the cell in our body are continuously growing, dividing and dying. Dead cells must be replaced with new cells. Process of every cells making a copy of itself through a process called mitosis. * Cork is dead at maturity and doesn't expand In plant : Meristematic tissue (terminal buds, vascular cambium, Vascular cambium Terminal buds cork cambium Cell division Nuclear division Cytoplasmic division ( cytokinesis ) Examples : 2. Developing of human zygote 3. Binary fission A human zygote developing into a foetus Zygote zygote begins to divide Binary fission The significance of mitosis Mitosis is the process of nuclear division which result in the formation of two genetically identical daughter nuclei. Significant of mitosis i. essential in replacing dead cells ii. Allows damage cell to be repaired, replaced and regenerated. Chromosomes and chromosomal number Cells Somatic cells gametes Somatic cells → mitosis reproductive cells (gametes) → meiosis Number of chromosomal - onion – 16 chromosomes - Drosophila – 8 chromosomes Chromosomes in nucleus exist in pairs = diploid. chromat id sentro mer In human, one set of chromosomes consists of 23 chromosomes. Hence , our somatic cells have 46 chromosomes arranged in 23 pairs or 2n=46. The two chromosomes in each pairs have the same structural features and are referred to as the homologous chromosomes. Each member of the matching pair is called homologue. One of the chromosomes is of paternal origin, whereas the other is of maternal CELL CYCLE The cell cycle is the period that extends from the time of new cell is produced until the time the cell completes a cell division. 2 major phase : interphase ( G1, S, G2 ) : M phase (mitosis + cytokinesis) CELL CYCLE MITOSIS ANIMATION INTERPHASE Accounts for 90% of cell cycle. G1 : Chromosomes are extremely fine and cannot be seen under light microscope. S : Synthesis of DNA occurs Prophase Metaphase anaphase telophase Cytokinesis STAGES OF MITOSIS The importance of controlled mitosis Genetic information carried by the chromosomes is necessary for the proper funtioning of an organisms. To ensure the genetic information content and the number of chromosomes in the parent cells are maintained in the daughter cells from one generation to the next. The rate and timing of cell division in animals and plants are important for The effects of uncontrolled mitosis When a cell divides through mitosis repeatedly, without control and regulation, it can produce cancerous cells. Cancer is a genetic disease cause by uncontrolled mitosis due to severe disruption to the mechanism that controls the cycle cells. Cancerous cell : - divides freely - compete with the surrounding normal cell to obtain sufficient nutrients and energy. - can intrude and spread to other tissue Cancer can be caused from : - damage to the DNA - mistakes that occurs in the genes - certain chemical compounds like tar and tobacco - carnigenic compound such as formaldehyde. Application on mitosis in cloning Cloning Tissue culture technique Cloning Process of producing clones or genetically identical copies of a cell, tissue or an organisms through asexual reproduction. Involve the transfer of the nucleus from a somatic cell to an ovum or embryonic cell which has the nucleus removed. Eg : first cloned → Dolly (1997) Tissue culture technique Tissue culture technique involves the growth of cells or tissues outside the cell in suitable medium (contain nutrients and growth hormone). Plant cell divides by mitosis to form callus (undifferentiated mass of tissue) Callus → embryo → plantlets. C allus New plantlets (shoots with leaves) are forming. A mass of callus tissue is formed that is just starting to make new plantlets. If the conditions are right a small "forest" of plants will develop in the tissue culture container. ADVANTAGES OF CLONING Allows biotechnologist to multiply copies of useful genes or clones. Can produced in shorter time and in large number . Many transgenic crops like wheat, soys bean which are resistant to herbicide, pests and disease have been created. Vegetative reproduction → does not need the pollinating agent Shorter period for plant that reproduce from seed Certain transgenic bacteria can be used to control environment pollution - some bacterial clones which are able to break down toxic waste material can help clean up toxic waste dump.