Eukaryotic Cell Cycle and Cell Division

Cell Division

process by which a cell divides to form two new cells (daughter cells)

Prokaryotes (bacteria)

Binary fission → divides forming two new identical cells

Eukaryotes

1. Mitosis

   a. Organism growth

   b. Replacement or repair of damaged cells

2. Meiosis

   a. Formation of sex cells, or gametes

Cell Cycle: Interphase

is the period of growth and DNA replication between cell divisions

Divided into three phases:

1. G₁ phase

2. S-phase

3. G₂ phase

What is the G₁ phase?

cell increases in size

What is the S phase?

replication of chromosomes

• two strands joined by a centromere

What is the G₂ phase?

• organelles double

• new cytoplasm forms

• all other structures needed for mitosis form

M Phase: Mitosis

Process that divided cell nucleus to produce two new nuclei each with a complete set of chromosomes

4 Phases of Mitosis

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

Mitosis

• cell division

• Follows S phase of cell cycle

• Cell grows from 4n after S to 2n after division

Major Check Points

1. In G₁ phase

   • is the DNA damaged?

2. In S phase

   • Is the DNA not replicated or damaged?

3. In G₂ phase

   • Is the DNA not replicated or damaged?

4. In M phase

   • Are the chromosome misaligned?

Cell Cycle Regulation

• Regulated by two protein complex

  • Cyclin

  • Cyclin-dependent kinase

  • Different complexes act at different stages of the cell cycle

  • Checkpoint regulators

• Lead to new developments in cancer research

Ubiquitin and Proteasome Route

HPV encodes a protein that activates a specific E3 enzyme.

• The enzyme ubiquitinates the tumor suppressor p53 and other proteins that control DNA repair, which are then destroyed.

• The activated of E3 enzyme is observed in more than 90% of all cervical carcinomas

Meiosis

• Gametes

• Reductional division to 1n

• Sperm

• Oocyte and polar bodies

Meiosis Errors

Aneuploidy: an abnormal number of chromosomes

Necrosis

• Accidental Death

• Cell lysis leads to intense inflammation

Apoptosis

• Programmed cell death

• Phagocytosis clears up debris