Lecture 12

• Eukaryotic Cell Cycle

  There are two phases

  • 1)Interphase (G1/s, G2)
  • G1= First gap
  • S= DNA synthesis
  • G2= Second gap
  • 2) Mitotic phase
• Eukaryotic Cell Cycle - Interphase 


  G1/S Phase:

  • Growth and gene expression occur
  • Chromosomes uncondensed

  G2 phase:

  • At late interphase, chromosomes have duplicated but cannot be distinguished individually
  • Centrosomes created
• Eukaryotic Cell Cycle- Mitotic phase

  Mitosis= Division of nucleus

  Cytokinesis= Division of cytoplasm
• Mitosis -Prophase

  Chromosomes condense

  Nucleolus disappears

  Mitotic spindle forms

  Sister chromatid

  • Two identical daughter copies of a chromosome made by DNA replication

  
• Mitosis- Prometaphase 


  Nuclear envelope fragments

  Kinetochores assemble on chromatids

  • Protein structures at centromere where microtubules attach
  • Sister chromatids also held together by cohesion proteins
  • Non- Kinetochore microtubules doesn't attach to centromere

  
• Mitosis- Metaphase


  Chromosomes line up at metaphase plate
• Mitosis- Anaphase 


  Chromatids separate pulled by kinetochore microtubules and move to opposite poles

  Non- kinetochore microtubules get longer to lengthen the cell

  • Helps with cell division

  Kinetochore microtubules shorten at the chromosome end

  
• Mitosis- Telophase and Cytokinesis


  Events of prophase/ pro metaphase undone

  Nucleus and nuclear envelope form

  Cytokinesis is when the cell split into two daughter cells

  
• Cytokinesis in Animal Cells

  Cell divides into two during cytokinesis.

  Follows nucleus division in mitosis.

  Cleavage furrow forms.

  Contractile ring contracts, pinching the cell into two.

  Two daughter cells form, each with own nucleus.

  Process completes, daughter cells continue growing.
• Cytokinesis in Plant cells

  • Cell splits: Cytokinesis divides one cell into two.

  • Follows nucleus division: Happens after mitosis.

  • Groove appears: Cleavage furrow marks the split site.

  • Actin ring tightens: Contractile ring contracts inside the cell.

  • Cell pinches: Membrane pulls inward.

  • Two new cells: Daughter cells form.

  • Each with own nucleus: New cells get complete genetic material.