Cell division

The role of mitosis
1. division of nucleus into two genetically identical daughter nuclei
2. all DNA in nucleus replicated before mitosis
  1. during interphase, before mitosis
  2. single DNA molecule to two chromatids
3. one chromatid to each daughter
4. Uses
  1. embryonic development
  2. growth
  3. tissue repair
  4. asexual reproduction
Interphase
1. active phase in metabolic processes
2. many processes in nucleus and cytoplasm
3. DNA replication in nucleus
4. protein synthesis in cytoplasm
5. numbers of mitochondria in cell increase due to growth and division
6. plant cells and algae
  1. chloroplasts increase
  2. cellulose formation and added to cell wall by vesicles
7. phases
  1. G1
    1. some never progress past this stage
      1. enter Gn
  2. S
    1. replication of genetic material in nucleus
  3. G2
Supercoiling of chromosomes
1. condensation of chromosomes
  1. pack chromosomes into shorter structures
  2. occurs during prophase
2. two chromatids move to opp. poles
3. DNA molecule
  1. diameter less than 5µm
  2. length 50,000 µm
4. repeatedly coiling of chromosomes to make them shorter and wider
5. assisted by histones and enzymes
Phases of mitosis
1. Prophase
  1. condensation of chromsomes
  2. breakdown of nucleolus
  3. microtubules grow from MTOC to form spindles
  4. nuclear membrane breaks down at the end
2. metaphase
  1. microtubules grow more and attach to centromeres
  2. chromatids attach to microtubule
  3. microtubules shorten; if correct, chromosomes stay at equator
3. anaphase
  1. each centromere divided, allowing sister chromatid pairs to separate
  2. spindle microtubules pull them to poles
  3. 2 genetically identical nuclei produced
4. telophase
  1. chromatids reach poles; called chromosomes
  2. chromosomes pulled into tight groups near MTOC at each pole
  3. nuclear membrane reforms around chromosomes
  4. chromosomes uncoil; nucleolus formed
  5. usually enters interphase again
Cytokinesis
1. occurs after mitosis
2. in plants
  1. vesicles fuse at equator to form tubular structure
  2. tubular structures fuse to form two membranes across equator
  3. division of cytoplasm
  4. pectin and other substances deposited between 2 membranes by exocytosis
    1. forms middle lamella; will link walls
  5. cellulose deposited to center by exocytosis
  6. each daughter cell builds own wall adjacent to equator
3. in animals
  1. plasma membrane pulled inwards around cell equator to form cleavage furrow
    1. using ring of contractile protein at equator
    2. actin and myosin
    3. pinched off into daughter cells
4. process of cell division
Cyclins and the control of the cell cycle
1. cyclins - group of proteins
2. ensure tasks are performed at correct time
3. bind to enzymes cyclin-dependent kinases
4. enzymes become active and attach phosphate groups to other proteins in the cell
  1. triggers protein to carry out specific task
5. stage progresses only if cyclin reaches threshold concentration
6. diagram in supplementary
Tumor formation and cancer
1. mutagens, oncogenes and metatstasis involved
2. tumor - abnormal group of cells
3. benign tumor - adhere to each other and unlikely to spread and cause harm
4. carcinomas/ malignant tumors - detach, move elsewhere, create secondary tumor, life threatning
  1. cause cancer; diverse causes
5. carcinogens - cancer causing chemicals and agents
6. all (chemical and high energy radiation) mutagens are carcinogenic
  1. cause gene mutation which can cause cancer
  2. X-rays & short ray UV light
7. mutations - random changes in base sequence
8. oncogenes - genes that cause cancer after mutation
  1. usually involved in control of cell cycle and division
  2. several mutations must occur at the same time for tumor cell
9. metastasis - movement of tumor cells from primary tumor to develop secondary tumor in other body parts
10. primary tumor - original group of tumor cells

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