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

Chromosomes

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

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

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)

Interphase

• Phase with highest metabolism (mitochondria have a high activity)
• Muscles never complete the whole cycle

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

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

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

Anaphase

• Spindle fibres pull copies of chromatids to spindle poles to separate them
• Mitochondria around spindle provide energy for movement

Telophase

• Chromatid at the pole
• Sets of chromosomes form new nuclei
• Chromosomes become long and thin, uncoil!
• Nuclear envelopes form around the nucleus