Cell Differentiation Is The Selective Expression Of Genes
- Multicellular organisms contain diverse cell types, all arising from a single zygote.
- Cell differentiation is the process by which cells become structurally and functionally specialized by selectively expressing genes.
- This enables division of labor in tissues and organs, increasing overall efficiency.
The "colors" are genes, and the "environment" provides the signals.
What Is Differentiation?
Definition
Differentiation
Differentiation is the process where pluripotent cells (unspecialized cells) develop into specialized cells with unique structures and functions.
- Despite all cells sharing the same DNA, differentiation ensures only specific genes are expressed in each cell type.
- Despite all cells in an organism sharing the same DNA, differentiation ensures that only specific genes are expressed in each cell type.
Cells from the placenta or umbilical cord during embryonic stages have the potential to specialize into nerve cells, muscle cells, or blood cells.
The Role of Gene Expression in Differentiation
Definition
Gene expression
Gene expression is the process of using genetic information to produce functional products like proteins.
- Gene expression is the process of using genetic information to produce functional products like proteins.
- Cells selectively "activate" certain genes while "silencing" others in response to:
- Internal cues: Signals from within the cell or its lineage.
- External cues: Environmental signals like hormones or growth factors.
- Muscle cells express genes for actin and myosin (proteins for contraction).
- Red blood cells activate the gene for hemoglobin (oxygen transport).
- Nerve cells express genes for neurotransmitter receptors.
Environmental Triggers for Gene Expression
1. Chemical Signals
- Environmental chemicals, such as hormones and growth factors, can bind to receptors on a cell’s surface.
- This triggers molecular cascades that influence gene expression.
- Erythropoietin (EPO), a hormone released during low oxygen levels, activates genes involved in red blood cell production.
- Insulin, secreted after a meal, regulates the expression of genes involved in glucose uptake and storage.
2. Physical Signals
- Physical factors, such as pressure or mechanical stress, also affect gene expression.
- Bone cells respond to mechanical stress by expressing genes that promote bone growth and repair.
- Skin cells exposed to ultraviolet (UV) light activate genes involved in DNA repair and melanin production.
3. Temperature and Light
- Environmental conditions like temperature and light directly influence gene expression.
- Arctic foxes express pigmentation genes differently based on seasonal light and temperature.
- This results in white fur during winter and brown fur in summer.
- Plants exposed to light express genes for photosynthesis, while those in darkness activate genes for energy conservation.
Why Differentiation Matters
- Differentiation enables the formation of tissues and organs with specialized functions.
- Allows organisms to respond to environmental changes and maintain survival.
- Errors in differentiation can cause serious issues like cancer, where cells lose specialization and proliferate uncontrollably.
- If every cell in an organism shares the same DNA, yet expresses it differently, what does this suggest about where “control” truly lies?
- In the genes themselves, or in the systems that interpret them?
- Explain why all cells in a multicellular organism have the same genome, yet differ in structure and function.
- Describe two examples of differentiated cells and identify the specific gene products that define their roles.
