Cell Cycle Control Quiz

Cell Cycle Control

• G1 Checkpoint: Evaluates cell's readiness to commit to division by assessing growth signals, nutrient availability, and DNA integrity.
  • Growth Signals: Hormones from nearby or distant tissues trigger signal transduction pathways leading to G1 progression.
    • Growth factors activate CDKs (cyclin-dependent kinases), which phosphorylate RB protein.
    • Phosphorylated RB releases E2F protein, activating genes needed for cell cycle progression.
  • Nutrient Availability: Adequate nutrients are essential for continued cell cycle progression.
    • Insufficient nutrients prevent RB phosphorylation, blocking E2F release and halting cell cycle progression.
  • DNA Integrity: Ensures accurate transmission of genetic information.
    • DNA damage activates CDKs to phosphorylate p53 protein, which binds to DNA and activates DNA repair proteins.
    • If damage is irreparable, p53 levels increase, eventually triggering apoptosis.

Apoptosis

• Programmed cell death that helps maintain normal cell levels in somatic cells, preventing tumor development.
• Caspases, enzymes responsible for apoptosis, are normally held in check by inhibitors.
• Internal or external signals deactivate inhibitors, leading to activation of caspases and cell death.

Chromosome Structure

• Chromatin: DNA and associated proteins that condense into chromosomes during cell division.
• Nucleosomes: DNA wrapped around histone protein spools, forming the basic unit of chromatin.
• Chromosomes: Condensed chromatin during mitosis, consisting of two sister chromatids joined by a centromere.
• Interphase: DNA is uncoiled and replicated during the S phase, but chromosomes are not visible.
• Mitotic Stage: Chromosomes become visible as doubled sister chromatids.

Mitosis

• Cell division producing two genetically identical daughter cells.
• Prophase: Chromosomes condense, nuclear envelope breaks down, and spindle fibers form.
• Metaphase: Chromosomes align at the metaphase plate, guided by spindle fibers.
• Anaphase: Sister chromatids separate and move to opposite poles of the cell.
• Telophase: Nuclear envelope reforms, chromosomes decondense, and cytokinesis begins.

Cytokinesis

• Division of the cytoplasm into two distinct daughter cells.
• Animal Cells: Cleavage furrow indents the plasma membrane, pinching off the two cells.
• Plant Cells: Cell plate forms between daughter cells, eventually becoming a cell wall.

Cancer Development

• Proto-oncogenes: Genes that promote cell cycle progression and inhibit apoptosis (like the gas pedal).
  • Mutations in proto-oncogenes convert them to oncogenes, increasing cell division and promoting cancer.
  • Examples: ras gene family, WNT, MYC, ERK, TRK (do not memorize all, just for understanding).
• Tumor Suppressor Genes: Genes that inhibit cell cycle progression and promote apoptosis (like the brakes).
  • Mutations in tumor suppressor genes can disrupt these functions, promoting uncontrolled cell growth.
  • Examples: RB (retinoblastoma), P53, BRCA1, BRCA2 (do not memorize all, just for understanding).

Other Cancer Origins

• DNA repair systems: Failure to repair DNA damage can lead to mutations and uncontrolled cell growth.
• Telomeres: Ends of chromosomes that normally shorten with each replication.
  • Telomerase: An enzyme that prevents telomere shortening, allowing cells to divide indefinitely.
  • Cancer cells often express telomerase, contributing to their uncontrolled proliferation.

Prokaryotic Cell Division

• Prokaryotic Chromosome: Single, circular chromosome located in the nucleoid region.
• Binary Fission: Asexual reproduction in prokaryotes, where the chromosome replicates, the cell elongates, and divides into two identical daughter cells.

Comparing Prokaryotic and Eukaryotic Cell Division