SCIENCEEE

• Mitosis


  Cell division that takes place in somatic cells
• Meiosis


  Cell division that takes place in ovaries and testes to form gametes
• New cells are formed through cell division, a discovery by Rudolf Virchow in 1858
• Cell division


  1. One cell divides and becomes two

  2. Two daughter cells grow in size and divide again to form four new cells

  3. Process repeats in the cell cycle
• Nucleus


  Control center of the cell that directs and coordinates all cellular activities
• Cell cycle


  • Divided into interphase and mitotic or M phase
  • Interphase is the resting stage where cell performs metabolic activities, grows, and replicates chromosomes
  • Interphase is divided into G1, S, and G2 subphases
• G1 subphase


  Cell undergoes physical growth, synthesizes proteins for chromosome replication and cell division
• S subphase


  Chromosomes are replicated, forming two identical sister chromatids
• G2 subphase


  Replicated chromosomes condense, additional cell growth and preparations for cell division
• Cell cycle duration varies in different cells: 24 hours in rapidly dividing human cells, 20 minutes in bacteria, 23 minutes in yeast
• Interphase cell


  • Nuclear membrane surrounds nucleus with visible nucleolus
  • Chromatin strands are thin and tangled
• Mitosis (M phase)


  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase
• Prophase


  1. Nuclear membrane and nucleolus begin to break down

  2. Chromatin strands contract and thicken into double-stranded chromosomes

  3. Centrioles move to opposite poles

  4. Spindle fibers develop
• Metaphase


  1. Double-stranded chromosomes align at the equator

  2. Each chromatid attached to spindle by kinetochore
• Anaphase


  Chromatids separate at centromere and migrate to opposite poles
• Telophase


  1. Chromosomes uncoil at poles

  2. Nucleolus and nuclear membrane reform

  3. Cytoplasm divides, forming two identical daughter cells
• Mitosis involves nuclear division (karyokinesis) and cytoplasm division (cytokinesis)
• G0 phase


  Resting phase outside the cell cycle, where new cells are not yet ready for another division
• Cells in G0 phase can remain quiescent for an indefinite period until stimulated to re-enter the cell cycle