Cell Growth and Division Quiz

Cell Growth and Division

• Cells divide for growth, repair, and development.
• Smaller cells have a higher surface area to volume ratio, which is more efficient for nutrient uptake and waste removal.
• Large cells struggle with material exchange and DNA access, thus requiring division.
• Cell division solves the problems of insufficient material exchange and DNA overload.

Cell Cycle

• The cell cycle is a series of events that cells undergo to grow and divide.
• It's divided into interphase and M phase.
• Interphase is the period between cell divisions and consists of G1, S, and G2 phases.
  • G1 (Gap 1) phase: Growth, protein and organelle synthesis.
  • S (Synthesis) phase: DNA replication, replication of key proteins like centromeres.
  • G2 (Gap 2) phase: Organelle and molecules needed for cell division are created.
• M phase: Mitosis and cell division.

Mitosis

• Mitosis is the division of the nucleus.
• Four main phases:
  • Prophase: Chromatin condenses into chromosomes, nuclear envelope and nucleolus break down, spindle fibers form.
  • Metaphase: Chromosomes align at the cell's equator, connected to spindle fibers at the centromere.
  • Anaphase: Sister chromatids separate and move to opposite poles.
  • Telophase: Chromosomes decondense, nuclear membranes reform, nucleoli reappear.
• Cytokinesis follows mitosis, dividing the cytoplasm and forming two daughter cells.
• Plant cells form a cell plate, creating a new cell wall between the two cells.

Cell Cycle Regulation

• Internal regulators (e.g., cyclins, CDKs) and external regulators (e.g., growth factors) control the cell cycle.
• Cyclins activate CDKs (cyclin-dependent kinases), enzymes that control cell cycle progression.
• Growth factors are external signals telling cells when to divide.
• Density-dependent inhibition: Cells stop dividing when they touch other cells.
• Anchorage dependence: Cells must be attached to a substratum to divide.

Cancer

• Cancer is uncontrolled cell growth and division.
• Tumors are masses of cancer cells. Benign tumors do not spread, malignant tumors do.
• Cancer is caused by various factors, such as carcinogens, radiation, viral infections, and genetics.
• A common factor in cancer is the malfunctioning control of the cell cycle.
• Cancer cells are not subject to density-dependent inhibition or anchorage dependence.
• Proto-oncogenes (normal genes controlling growth) can mutate into oncogenes, leading to uncontrolled growth.
• Tumor suppressor genes (e.g., p53) prevent uncontrolled cell division by detecting and repairing damaged DNA.

Cancer Treatment

• Cancer treatments may target the affected area (surgery, radiation) or affect overall cells (hormone therapy, chemotherapy, targeted therapy/immunotherapy).

Chromosome Structure and Replication

• Before entering the cell cycle, chromosomes are duplicated.
• The duplicated chromosomes are called sister chromatids.
• The centromere holds the sister chromatids together.
• This means that after replication, the number of chromosomes doesn't change, but the number of chromatids doubles.
• Prokaryotes replicate their single circular chromosome through binary fission, which is distinct from mitosis.

Cell Size and Ratio

• SA:V (surface area to volume ratio) decreases as a cell increases in size.
• This affects how efficient cells are at exchanging materials with their surroundings.
• Small cells are more efficient at carrying out these exchange functions.