lecture 14

Cell Cycle Control & Mitosis

• Learning Objectives: Students will understand the significance of different cell cycle phases and correlate them with normal and abnormal cell division outcomes.

Cell Cycle Control

• Cell cycle progression is regulated by cyclins and cyclin-dependent kinases (CDKs).
• Cyclin D binds to CDK4 and CDK6 in early G1.
• Cyclin E binds to CDK2 in late G1, allowing entry into S phase.
• Cyclin A binds to CDK2 and CDK1 to facilitate progression from S to G2.
• Cyclin B binds to CDK1 to allow entry from G2 to M phase.

Cell Cycle Checkpoints

• Checkpoints ensure proper DNA replication, growth, and chromosome segregation before allowing cell cycle progression.
• Factors stimulating cell cycle entry may include mechanical force, tissue injury, and cell death.
• These factors often involve the release of growth factors, influencing the activity of proto-oncogenes, which regulate cell proliferation.

Clinical Significance (Oncogenes & Cancer)

• Proto-oncogenes regulate normal cell proliferation.
• Mutations in these genes can lead to uncontrolled cell growth, forming oncogenes and contributing to cancer development.
• Oncogene alterations can involve DNA mutations, gene amplification, or rearrangements.

Chromosomes

• Chromosomes are highly condensed chromatin fibers visible during mitosis and meiosis.
• Each chromosome consists of two sister chromatids joined at the centromere.
• Chromosomes contain DNA, packaged with proteins (histones).

Mitosis

• Mitosis is cell division resulting in two identical daughter cells.

• Stages of mitosis:

  • Prophase: Chromosomes condense, nucleolus disappears, centrosomes move to opposite poles.
  • Metaphase: Chromosomes align at the cell's equator.
  • Anaphase: Sister chromatids separate and move towards opposite poles.
  • Telophase: Chromosomes decondense, nuclear envelope reforms, and cytokinesis occurs, dividing the cytoplasm into two daughter cells.

• Cytokinesis follows mitosis and divides the cytoplasm.

• The cell cycle ensures accurate DNA replication and distribution during cell division.

Clinical Correlations

• Understanding the cell cycle is crucial for cancer chemotherapy, where drugs target specific cell cycle stages.
• Drugs like vincristine disrupt the mitotic spindle, while colchicine prevents microtubule formation, both arresting cell division.
• Karyotyping uses colchicine to study individual chromosomes.

This quiz explores the critical phases of the cell cycle, including the roles of cyclins and CDKs in regulating cell division. It also discusses the significance of cell cycle checkpoints and their clinical relevance in cancer and oncogenes. Test your knowledge on how these processes affect normal and abnormal cell proliferation.