BYA3 SECTION 12.4Cell division - Genetic information is passed from cell to cell during division |
New cells arise by division of existing cells |
- Cell division occurs in the nucleus of eukaryotic cells by mitosis and meiosis
- Replacement of the entire lining of your small intestine
- Liver cells only divide for repairing
- Nerve cells do not divide
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Chromosomes |
- Long and thin for replication and decoding
- Become short and fat prior mitosis → easier to separate due to compact form
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Meiosis (reduction division) |
- During the production of sex cells (gametes) in animals
- In spore formation which precedes gamete production in plants
- Haploid gametes (sperm ovum) - sexual reproduction
- DNA in a cell replicates only once, but cell divides twice
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The Cell Cycle |
- Interphase
- G1: Protein synthesis and growth (10 hours)
- Preparation for DNA replication (e.g. growths of mitochondria)
- Differentiation, only selected genes are used to perform different functions in each cell
- S: DNA Replication (9 hours)
- G2: short gap before mitosis, organelles and proteins for mitosis are made (4 hours)
- G0: Resting phase (nerve cells)
- M-phase
- Mitotic division of the nucleus (Prophase, Metaphase, Anaphase, Telophase)
- Cytokinesis (division of the cytoplasm)
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Interphase |
- Phase with highest metabolism (mitochondria have a high activity)
- Muscles never complete the whole cycle
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Mitosis |
- Process of producing 2 diploid daughter cells with the same DNA by copying their chromosomes (clones)
- Chromosomes can be grouped into homologous pairs
- Mitosis occurs in
- Growth
- Repair
- Replacement of cells with limiting life span (red blood, skin cells)
- Asexual replacement
- Controlled process, cancers result from uncontrolled mitosis of abnormal cells
- Division of the nucleus (karyokinesis) and the cytoplasm (cytokinesis) are two processes of mitosis
- Division of cytoplasm after nucleus. Delayed if cells have more than one nucleus (muscle)
- Active process that requires ATP
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Prophase |
- Chromosomes become shorter and thicker by coiling themselves (condensation)
This prevents tangling with other chromosomes
- Nuclear envelope disappears/breaks down
- Protein fibres (spindle microtubules) form
- Centrioles are moving toward opposite poles forming the spindle apparatus of microtubule
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Metaphase |
- Centrioles at opposite poles
- Chromosomes line up on the equator of the spindle
- Centromeres (kinetochores) attach to spindle fibres
- Kinetochores consist of microtubules and "motor" proteins which utilise ATP to pull on the spindle
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Anaphase |
- Spindle fibres pull copies of chromatids to spindle poles to separate them
- Mitochondria around spindle provide energy for movement
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Telophase |
- Chromatid at the pole
- Sets of chromosomes form new nuclei
- Chromosomes become long and thin, uncoil!
- Nuclear envelopes form around the nucleus
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Cytokinesis |
Plant Cells |
Animal Cells |
- Cell plate forms and contains cell wall materials
- Remains of spindle
- Vesicles formed by Golgi apparatus |
- Region of constriction
- Actin molecules (ring) contract |
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References and Further Reading
AQA (2006) GCE Biology/Biology (Human) 2006 specification, [PDF]