How cells differentiate: gene expression and signals
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Question
What is differentiation?
Answer
The process by which an **unspecialized cell becomes a specialized cell** with a particular structure and function.
Question
Do all body cells of an organism have the same genome?
Answer
**Yes** — every body cell carries the same complete set of genes (the same genome).
Question
If the genome is the same in every cell, what makes cell types differ?
Answer
**Different genes are expressed** (switched on) in each cell type — not different genes present.
Question
What is gene expression?
Answer
Switching a gene **'on'** so it is used to make its **protein**. An expressed gene is active; an unexpressed gene is silent.
Question
What is selective gene expression?
Answer
Expressing **only some** of the genes in the genome — different genes in different cell types — so each cell makes only the proteins it needs.
Question
What tells a cell which genes to switch on during development?
Answer
**Chemical signal gradients** — the concentration of signalling molecule a cell meets depends on its **position**.
Question
What is a concentration gradient of a signal?
Answer
A smooth change in the concentration of a signalling molecule — **high near its source**, lower further away.
Question
How does position in a gradient affect a cell?
Answer
A cell's **position** sets the **signal concentration** it meets, which switches on a **particular set of genes**, deciding the cell type it becomes.
Question
What is the outcome when an unspecialized cell meets a signal gradient?
Answer
It **differentiates** — switching on specific genes and becoming a specialized cell type.
Question
Why do expressed genes make a cell specialized?
Answer
The genes switched on are used to make **specific proteins**, which give the cell its specialized **structure and function**.
Question
Are genes deleted from a cell when it differentiates?
Answer
**No** — unused genes are switched **off**, not removed. The cell keeps the full genome.
Question
State the cause-and-effect chain of differentiation.
Answer
Position in gradient → **signal concentration** detected → **genes** switched on → **proteins** made → specialized **cell type**.
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Cell specialization
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