Lecture_26_Cell cycle & Karyotype

Lecture 26: Cell Cycle & Karyotype

Learning Outcomes

  • Reasons for Cell Division: Understand why cells divide

  • Key Events in Cell Division: Identify the four main steps during cell division

  • Prokaryotic Division: Describe how prokaryotic cells divide through binary fission and the role of the FtsZ protein

  • DNA Replication: Explain how DNA is copied in both prokaryotes and eukaryotes

  • Cytokinesis: Discuss how the cytoplasm divides after the nucleus has divided in prokaryotes and eukaryotes

  • Cell Cycle Phases: Learn the different phases of the cell cycle (G1, S, G2, and M phase)

  • Cell Cycle Regulation: Understand how the cell cycle is controlled by cyclins, CDKs, and checkpoints

  • Karyotype: Identify chromosomal structures and understand human chromosome count and abnormalities

Reasons for Cell Division

  • Key Processes: Cell division occurs for fertilization, growth, wound healing, regeneration, and reproduction.

Four Major Events of Cell Division

  1. Signals for Division: Internal or external cues that prompt cells to divide.

  2. DNA Replication: Cells double their genetic material.

  3. Distribution of DNA: Ensures each new cell gets the correct genetic information.

  4. Cytokinesis: The final step where the cell divides into two.

Prokaryotic Division: Binary Fission

  • Triggers for Division: Nutrients and environmental factors.

  • DNA and Replication: Bacteria have circular DNA that starts replication at an origin (Ori) and moves to a termination point (Ter).

  • Segregation of DNA: Newly formed DNA moves to opposite sides of the cell.

  • Cytokinesis: The FtsZ protein creates a ring that helps split the cell.

Eukaryotic Division

  • Mechanism: Eukaryotic cells divide through mitosis followed by cytokinesis.

  • Signals for Division: Unicellular organisms divide like bacteria; multicellular ones receive signals from their surroundings.

  • DNA Structure: Eukaryotes have many linear chromosomes.

  • Cytokinesis: In animals, the cell membrane pinches; in plants, a cell plate forms.

Overview of the Cell Cycle

  • Interphase: Preparation phase; includes G1, S, and G2 phases, making up most of the cycle.

  • Mitosis: The active division phase.

  • G0 Phase: A resting state where cells do not divide but can do so under certain conditions.

Discovery of Cell Cycle Regulatory Molecules

  • 1970s Findings: Research on fused cells led to discoveries about how cells control their cycle.

Cyclins and M-phase Promoting Factor (MPF)

  • Cyclins: Proteins that activate MPF (needed for cells to enter mitosis).

  • MPF Activation: Cyclins bind to CDKs, leading to cell division.

  • Deactivation: MPF is turned off to prevent ongoing division.

Cell Cycle Checkpoints

  • Role of Checkpoints: They ensure the cells are ready to divide without errors.

Tumor Suppressors and Growth Factors

  • Tumor Suppressors: Proteins that stop the cycle if there is damage.

  • Examples of Growth Factors: Substances that promote cell division in specific situations, like healing or blood production.

Human Karyotype and Ploidy

  • Karyotype: The full set of human chromosomes (46 total, 22 pairs and 2 sex chromosomes).

  • Ploidy: Refers to how many sets of chromosomes exist in a cell (e.g., diploid means 2 sets).