What Are Stem Cells?
An undifferentiated cell that has the ability to divide and develop into many different specialised cell types in the body.
Most cells in your body are specialised — a muscle cell looks and behaves completely differently from a nerve cell or a red blood cell. But stem cells are different. They are like biological "blank slates" that haven't yet committed to a specific role.
Stem cells have two critical properties that make them unique:
- Self-renewal — they can divide to produce more copies of themselves (mitosis), maintaining a pool of unspecialised cells.
- Differentiation — under the right conditions, they can develop into specialised cell types with specific structures and functions.
Think of a stem cell like a raw piece of clay. On its own, it has no fixed shape or purpose. But depending on how it is shaped and treated, it can become a cup, a plate, or a sculpture — just as a stem cell can become a heart muscle cell, a neuron, or a skin cell.
Differentiation: From Blank Slate to Specialised Cell
The process by which an unspecialised cell becomes a specialised cell with a specific structure and function, by switching certain genes on or off.
Every cell in your body contains the same DNA — the complete set of genetic instructions. What makes a liver cell different from a skin cell is not which genes they have, but which genes are expressed (switched on or off).
During differentiation:
- Certain genes are activated, causing the cell to produce specific proteins.
- These proteins change the cell's shape, internal structures, and behaviour.
- Once differentiated, most cells cannot revert back to an unspecialised state under normal conditions.
Example: Red Blood Cell Differentiation
A stem cell in the bone marrow can differentiate into a red blood cell (erythrocyte). During this process:
- The cell loses its nucleus to make more room for haemoglobin.
- It becomes biconcave (disc-shaped) to maximise surface area for oxygen absorption.
- It fills with haemoglobin protein to carry oxygen.
The resulting red blood cell is perfectly specialised for gas transport — a function the original stem cell could not perform.
A common misconception is that differentiation changes the cell's DNA. It does not — all body cells retain the full genome. Differentiation is about gene expression, not gene changes.
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