A-Level Biology: Cell Division

A-Level Biology: Cell Division

1. 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

2. Chromosomes

   • Long and thin for replication and decoding
   • Become short and fat prior mitosis
     • easier to separate due to compact form

3. 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

4. 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)

5. 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
     • Asexual replacement
     • Replacement of cells with limiting life span (red blood, skin cells)
   • 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
   • Phases
     • Prophase
     • Metaphase
     • Anaphase
     • Telophase

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