This cheat sheet covers the major types of stem cells and how they become specialized cells in the body. Students need it to compare potency levels, understand sources of stem cells, and connect differentiation to gene regulation. It is useful for reviewing development, tissue repair, biomedical research, and ethical questions in modern biology.
The core idea is that stem cells vary in what they can become, from totipotent cells that can form an entire organism to unipotent cells with one main cell fate. Differentiation happens when certain genes are turned on or off, causing cells to make specific proteins and perform specialized functions. Signals from nearby cells, the extracellular environment, and internal transcription factors guide cell fate decisions over time.
Key Facts
- Totipotent stem cells can form all body cell types plus extraembryonic tissues such as the placenta.
- Pluripotent stem cells can form any body cell type from the three germ layers but cannot form a complete organism by themselves.
- Multipotent stem cells can produce several related cell types within one tissue or organ system.
- Unipotent stem cells usually produce one specialized cell type but can still self-renew.
- Embryonic stem cells are pluripotent cells taken from the inner cell mass of a blastocyst.
- Adult stem cells are usually multipotent or unipotent and help maintain and repair specific tissues.
- Differentiation occurs when selective gene expression leads to specialized structures and functions in a cell.
- Induced pluripotent stem cells, or iPS cells, are adult cells reprogrammed to a pluripotent state by changing gene expression.
Vocabulary
- Stem cell
- A cell that can self-renew and produce one or more types of specialized cells.
- Potency
- The range of different cell types that a stem cell can become.
- Differentiation
- The process by which an unspecialized cell becomes a specialized cell with a specific structure and function.
- Self-renewal
- The ability of a stem cell to divide and make more stem cells of the same type.
- Gene expression
- The process of using information in DNA to make functional products, usually proteins, that affect cell traits.
- Cell fate
- The final specialized identity and role that a developing cell adopts.
Common Mistakes to Avoid
- Confusing pluripotent with totipotent is wrong because pluripotent cells cannot form extraembryonic tissues needed to make a complete organism.
- Saying all stem cells can become any cell type is wrong because adult stem cells are usually limited to related cell types in a tissue.
- Thinking differentiation changes the DNA sequence is wrong because most specialized cells keep the same DNA but express different genes.
- Assuming embryonic stem cells and adult stem cells have the same potency is wrong because embryonic stem cells are typically pluripotent while adult stem cells are usually multipotent or unipotent.
- Forgetting the role of cell signals is wrong because differentiation depends on transcription factors, chemical signals, and the cell’s environment.
Practice Questions
- 1 Rank these potency levels from most flexible to least flexible: multipotent, totipotent, unipotent, pluripotent.
- 2 A hematopoietic stem cell can produce red blood cells, white blood cells, and platelets. What potency level does this example show?
- 3 If a skin cell is reprogrammed into an induced pluripotent stem cell, what major change has happened to its gene expression and developmental potential?
- 4 Why can two cells in the same organism have the same DNA but different structures and functions?