Cancer and Cell Cycle Preparation Notes

Understanding Cancer and the Cell Cycle

• Definition of Cancer

  • Cancer is characterized by uncontrolled cell growth and proliferation.

• Basic Cell Cycle Overview

  • The cell cycle is a fundamental process in all living organisms (excluding bacteria), where one cell reproduces to form two identical daughter cells.
  • DNA replication is crucial for cell division, as it encodes genetic information necessary for creating daughter cells.

Cell Cycle Phases

• Key Processes

  • DNA Duplication: The process begins with duplicating DNA to ensure each daughter cell receives an identical set.
  • Chromosome Segregation: Involves separating duplicated DNA into two groups.
  • Cytokinesis: This final step divides the cell's cytoplasm, resulting in two separate cells.

• Cell Growth

  • Along with DNA, proteins and organelles must also be duplicated to ensure the proper cell size and function.
  • Protein synthesis often takes the most time during the cell cycle and is closely coupled with DNA replication.

Phases of the Cell Cycle

• Interphase

  • The longest phase where cellular activities occur, though no visible changes under a microscope are observed.
  • DNA replication occurs here, producing duplicated genomes.

• M Phase (Mitosis)

  • Visible cell division with distinct morphological changes:
  • Prophase: Chromatin condenses into chromosomes, the nuclear envelope dissolves.
  • Metaphase: Chromosomes align at the cell's center. Here, checkpoints ensure proper attachment of chromosomes to spindle fibers.
  • Anaphase: Sister chromatids are pulled apart to opposite sides of the cell.
  • Telophase: Nuclear membranes reform, leading up to cytokinesis.
  • Cytokinesis: The cell physically divides into two daughter cells.

Checkpoints in the Cell Cycle

• Importance of Checkpoints

  • Ensure the cell cycle progresses accurately without mutations or errors.
  • In metaphorical terms, checkpoints act as security measures: they prevent the cycle from advancing if there are problems, such as DNA damage or improper segregation.

• G1 Checkpoint:

  • Determines whether a cell should proceed to S phase and begin DNA replication, often influenced by nutrient availability.

• G2 Checkpoint:

  • Ensures DNA has been accurately replicated and repairs any damage before proceeding to mitosis.

Model Organisms in Cell Cycle Research

• Yeast

  • Often used for studying the cell cycle due to their quick division (approximately every 30 minutes) and simpler genome.
  • Two types of yeast, fission and budding yeast, have been instrumental in identifying cell cycle genes (CDC genes) due to their manageable size and simplicity.

• Frog Oocytes

  • The large size and rapid maturation of frog eggs allow for effective study of the cell cycle without typical G1 and G2 phases, focusing on rapid S and M phases.

Cancer and Checkpoint Regulation

• Cancerous Cells

  • Tumor cells often have mutations in genes responsible for cell cycle checkpoints, leading to unchecked proliferation.

• Tumor Suppressor Genes

  • These genes encode proteins that regulate the cell cycle, preventing uncontrolled division. Loss or mutation of these genes can result in cancer.

Methods of Studying the Cell Cycle

• Fluorescent and Radioactive Labeling

  • Techniques like using bromodeoxyuridine (BrdU) allow researchers to identify dividing cells by labeling newly synthesized DNA.

• Flow Cytometry

  • A sophisticated technique to measure DNA content in individual cells to determine their phase in the cell cycle.

• Cell Culture Observations

  • Cell shape and attachment properties are indicative of their cell cycle phase. For instance, cells in mitosis appear round and detached.

Summary of Key Concepts

• The cell cycle is tightly regulated with specific phases and checkpoints to ensure accurate division. Errors can lead to cancer, where regulatory checkpoints are bypassed, leading to uncontrolled growth.