Cell division in eukaryotic and prokaryotic cells

• What are the three stages in the cell cycle ?

  Interphase - dna replication a

  mitosis - nuclear division

  cytokinesis - cell division, cytoplasm contents seperate into two daughter cells
• the movement from one phase to the next is triggered by chemical signals called cyclins
• interphase

  cell growth and DNA replication

  • G1 phase - cell preparing to replicate DNA
  • s phase - synthesis of new dna - dna replication
  • G2 phase - cell growth continues and DNA is checked for any errors
• what is the importance of mitosis ?

  Growth of multicellular organisms

  replacement of cells and repair of tissues

  asexual reproduction
• what are the stages of mitosis?

  prophase

  metaphase

  anaphase

  telophase
• Prophase:

  • Chromosomes condense and become visible when stained
  • Chromosomes consist of two identical chromatids called sister chromatids, each containing one DNA molecule joined at the centromere
  • Two centrioles move towards opposite poles, spindle fibres begin to emerge from them
  • Nuclear envelope breaks down into small vesicles
• Metaphase:

  • Centrosomes reach opposite poles
  • Chromosomes line up at the equator of the spindle
  • Spindle fibres attach to the centromeres of the chromosomes
• Anaphase: The spindle fibres contract, pulling the sister chromatids to opposite poles the chromatids assume a v-shape as they are pulled to each end of the poles (this process requires ATP from the surrounding mitochondria)
• Telophase:

  • Chromatids arrive at opposite poles and decondense
  • Nuclear envelopes begin to reform around each set of chromosomes
  • Spindle fibres break down
• Cytokinesis

  The cell divides forming two genetically identical daughter cells.
• How do you find the mitotic index ?

  The mitotic index is the proportion of cells (in a group of cells or a sample of tissue) that are undergoing mitosis.

  Mitotic index = number of cells with visible chromosomes / total number of cells
• Carcinogens are agents that may cause cancer, such as UV light, tar in tobacco smoke, and X-rays
• Examples of carcinogens include UV light, tar in tobacco smoke, and X-rays
• • Malignant tumour cells can break off the tumour and travel through the blood and / or lymphatic systemto form secondary growths in other parts of the body
• • The spreading of cancers in this way is known as metastasis
• binary fission

  replication of circular DNA

  replication of plasmids

  division of cytoplasm to produce two daughter cells
• viral replication

  viruses use their attachment proteins on its surface to bind to complementary receptor proteins on the surface of a host cell

  the virus then injects its DNA or RNA into the host cell

  the host cell then uses it nuclei acids and ribosomes to produce new viral particles

  the host cell busts (lysis) releasing the new viral particles
• what are some cancer treatments ?

  Most cancer treatments work by controlling the rate of mitosis

  • methotrexate - inhibits the synthesis of DNA nucleotides in cells (prevents DNA replication)
  • vincristine and taxol - prevents the formation of the mitotic spindle In metaphase.