Stem Cells

• What is cell specialization?


  It is a fundamental process in the development of multicellular organisms.
• What happens to a zygote after fertilization?


  A zygote undergoes rapid cell division to form a ball of unspecialized cells.
• What is the process called when unspecialized cells become specialized cells?


  This process is called differentiation.
• What controls the differentiation process in cells?


  The differentiation process is largely controlled by gene expression influenced by chemical gradients.
• How do chemical gradients influence cell differentiation?


  They act like a coordinate system, telling cells where they are and what they should become.
• What role does the protein Bicoid play in fruit fly embryos?


  Bicoid determines which end of the embryo will become the head based on its concentration gradient.
• What are the four types of stem cells based on their potency?

  Totipotent, pluripotent, multipotent, and unipotent stem cells.
• What is the spectrum of "stemness" in stem cells?

  • Totipotent: Can form all cell types (e.g., zygote)
  • Pluripotent: Can form most cell types (e.g., embryonic stem cells)
  • Multipotent: Can form multiple cell types within a lineage (e.g., hematopoietic stem cells)
  • Unipotent: Can form only one cell type (e.g., skin stem cells)
• What are the two key properties of stem cells?


  Self-renewal and potency.
• What is the role of telomerase in stem cells?


  Telomerase prevents the shortening of telomeres during cell division.
• What are stem cell niches?


  Specialized microenvironments that maintain and regulate stem cells in adult tissues.
• What is the function of the bone marrow niche?


  • Supports hematopoietic stem cells (HSCs)
  • Maintains HSCs in a quiescent state
  • Promotes HSC self-renewal when needed
  • Regulates HSC differentiation into various blood cell lineages
• What is the function of the hair follicle niche?


  • Contains epithelial stem cells for hair growth
  • Maintains hair follicle stem cells during resting phase
  • Activates stem cells to initiate hair growth
  • Regulates balance between stem cell maintenance and differentiation
• How are stem cells classified based on their potency?

  • Totipotent: Can form all cell types, including embryonic and extraembryonic tissues
  • Pluripotent: Can form all cell types of the embryo proper, but not extraembryonic tissues
  • Multipotent: Can form multiple cell types within a specific lineage
• What is the difference between totipotent and pluripotent stem cells?


  Totipotent cells can form a complete organism, while pluripotent cells cannot.
• What happens to stem cells in early-stage animal embryos?

  They start as totipotent but quickly become pluripotent as the embryo develops.
• How does cell size vary among different cell types in humans?


  • Gametes: Male ~3-4 μm, Female ~100 μm
  • Blood Cells: Red ~7-8 μm, White ~10-30 μm
  • Neurons: Cell body ~4-100 μm, Axon up to 1 meter
  • Striated Muscle Fibres: Diameter ~10-100 μm, Length up to 30 cm
• Why are sperm cells tiny compared to egg cells?


  Sperm cells are tiny to be mobile and penetrate the egg, while egg cells are large to contain nutrients.
• What is the significance of surface area-to-volume ratios in cells?


  It limits the cell's ability to exchange materials with its environment as the cell grows.
• What happens to the surface area-to-volume ratio as a cell grows?


  The volume increases faster than the surface area.