Cell Division Functions in Reproduction, Growth, and Repair
Cell division involves the distribution of identical genetic material, DNA, to two daughters cells. What is most remarkable is the fidelity with which the DNA is passed along, without dilution or error, from one generation to the next.
Core Concepts:
- All Organisms Consist of Cells and Arise from Preexisting Cells
- Mitosis is the process by which new cells are generated.
- Meiosis is the process by which gametes are generated for reproduction.
- The Cell Cycle Represents All Phases in the Life of a Cell
- DNA replication (S phase) must precede mitosis, so that all daughter cells receive the same complement of chromosomes as the parent cell.
- The gap phases separate mitosis from S phase. This is the time when molecular signals mediate the switch in cellular activity.
- Mitosis involves the separation of copied chromosomes into separate cells
- Unregulated Cell Division Can Lead to Cancer
- Cell-cycle checkpoints normally ensure that DNA replication and mitosis occur only when conditions are favorable and the process is working correctly.Mutations in genes that encode cell-cycle proteins can lead to unregulated growth, resulting in tumor formation and ultimately invasion of cancerous cells to other organs.
Significance
Mitosis is important for the maintenance of the chromosomal set; each cell formed receives chromosomes that are alike in composition and equal in number to the chromosomes of the parent cell.Following are the occasions in the lives of organism where mitosis happens: Development and growth: The number of cells within an organism increase by mitosis. This is the basis of the development of a multicellular body from a single cell i.e., zygote and also the basis of the growth of a multicellular body.
Cell Replacement: In some parts of body, e.g. skin and digestive tract, cells are constantly sloughed off and replaced by new ones. New cells are formed by mitosis and so are exact copies of the cells being replaced. Similarly, RBCs have short life span (only about 4 months) and new RBCs are formed by mitosis.
Regeneration: Some organisms can regenerate their parts of bodies. The production of new cells is achieved by mitosis. For example; sea star regenerates its lost arm through mitosis.
Asexual Reproduction: Some organisms produce genetically similar offspring through asexual reproduction. For example; hydra reproduces asexually by budding. The cells at the surface of hydra undergo mitosis and form a mass called bud. Mitosis continues in the cells of bud and it grows into a new individual. The same division happens during asexual reproduction or vegetative propagationin plants.
Terminology for Mitosis:
- gene - basic unit of heredity; codes for a specific trait
- locus - the specific location of a gene on a chromosome (locus - plural loci)
- genome - the total hereditary endowment of DNA of a cell or organism
- somatic cell - all body cells except reproductive cells
- gamete - reproductive cells (i.e. sperm & eggs)
- chromosome - elongate cellular structure composed of DNA and protein - they are the vehicles which carry DNA in cells
- diploid (2n) - cellular condition where each chromosome type is represented by two homologous chromosomes
- haploid (n) - cellular condition where each chromosome type is represented by only one chromosome
- homologous chromosome - chromosome of the same size and shape which carry the same type of genes
- chromatid - one of two duplicated chromosomes connected at the centromere
- centromere - region of chromosome where microtubules attach during mitosis and meiosis
Chromosome structure
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