6 : Cell Division

• Before cell division occurs, chromosomes appears as thread-like structures knows as chromatin.
• Interphase consists of three stages: G1 phase, S phase, and G2 phase.
• The process of mitosis involves four stages: prophase, metaphase, anaphase, and telophase.
• Chromatin consists of single DNA strand and proteins.
• Chromatin cannot be seen under microscope.
• Karyokinesis involves the division of the nucleus.
• Cytokinesis involves the division of the cytoplasm.
• Somatic cells are produced through mitosis process.
• Gametes are produced through the meiosis process.
• Somatic cells contains a diploid number of chromosomes, 2n = 46 ( in human )
• Gametes contains haploid number of chromosomes, n = 23 ( in human ).
• A pair of paternal and maternal chromosomes are called homologous chromosomes.
• Interphase is the longest phase in the cell cycle.
• What happens during G1 phase?

  • Cell grows
  • Cell multiplies the number of organelles in the cytoplasm
• What happens during S phase?

  • DNA replication
  • Each chromosome multiplies into two identical chromosomes (sister chromatids)
  • Both chromatids are joined at the centromeres
  • Multiplication of centriole
• What happens during G2 phase?

  • Cell continues to grow
  • More proteins and enzymes are synthesised
  • Cell pepares to divide
• What happens during M phase?

  Cell division — prophase, metaphase, anaphase, telophase
• Mitosis is defined as the division of the nucleus of parent cell into two division in somatic nuclei.
• In prophase, chromatin starts to shorten and thicken.
• The chromosome in prophase is made up of two identical threads called sister chromatids.
• During prophase, the nucleus membrane disintegrates, nucleolus disappears, centriole moves to the opposite poles and spindle fibres start to form.
• In metaphase, the chromosomes lined up on the equatorial plane.
• During metaphase, spindle fibres maintain the chromosomes at the equatorial plane.
• Metaphase ends when the centromere begins to divide.
• The centromere divides into two and the sister chromatids separate during anaphase.
• In anaphase, the spindle fibres shorten, contract and pull the sister chromatids to opposite poles.
• Anaphase ends when the chromatid arrives at the pole of the cell.
• Chromosomes are shaped again as fine chromatin threads at the start of telophase.
• Nucleoli reforms and spindle fibres disappear during telophase.
• New nucleus membrane reforms to surround the new daughter chromosomes in telophase.
• The telophase stage is followed by cytokinesis to form two daughter cells.
• Mitosis in plant cells does not require the presence of centrioles for formation of spindle fibres. Instead, they separate using a new cell wall.