Cell Differentiation and Cancer
Your body has about 200 types of cells, from nerve cells to muscle cells to red blood cells. Yet every one of them started from a single fertilized egg. How can cells with the same DNA look and work so differently? And what happens when a cell stops following the rules and keeps dividing? By the end of this page, you will be able to answer both questions.
One genome, many cell types
Cell differentiation is the process by which a cell becomes specialized in structure and function. A fertilized egg divides again and again by mitosis. Early cells can become almost anything. As the embryo develops, cells follow different paths and become specialized.
Stem cells are unspecialized cells that can divide and differentiate into specialized cell types. Embryonic stem cells can become almost any cell type. Adult stem cells, such as those in bone marrow, replace worn-out cells like blood cells.
Here are some examples of specialized cells:
| Cell type | Special feature | Function |
|---|---|---|
| Nerve cell (neuron) | Long axon and branching dendrites | Sends electrical signals |
| Muscle cell | Many protein fibers that shorten | Contracts to produce movement |
| Red blood cell | Disk shape, no nucleus, full of hemoglobin | Carries oxygen |
| Skin cell | Flat, tightly packed, makes keratin | Protects the body |
Structure matches function. A neuron's long axon fits its job of sending signals over long distances.
Define cell differentiation*. Then name one example of a specialized cell in an animal and state its function.
Define cell differentiation. Then name one example of a specialized cell in an animal and state its function.
A human skin cell and a human nerve cell contain the same DNA, yet they look and work very differently. State in one or two sentences what makes the two cells different…
A human skin cell and a human nerve cell contain the same DNA, yet they look and work very differently. State in one or two sentences what makes the two cells different from each other.
Gene expression and the environment
Think of your DNA as a huge cookbook. Every cell owns the whole book, but each cell type uses only certain recipes. Gene expression means using a gene to make a protein (transcription, then translation). In differential gene expression, different cell types turn on different sets of genes.
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A muscle cell expresses genes for contractile proteins.
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A red blood cell expresses the gene for hemoglobin.
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A neuron expresses genes for ion channels and signaling molecules.
The genes that are "off" are still there. The cell just does not use them. That is why a skin cell and a nerve cell share a genome but make different proteins.
Environmental factors
Which genes turn on depends partly on the cell's surroundings:
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Chemical signals from nearby cells. Cells close to a signaling group get a strong signal and follow one path. Cells farther away get a weak signal and follow another.
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Temperature. In some reptiles, incubation temperature affects whether an embryo develops as male or female.
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Nutrients and chemicals the cell is exposed to.
All the cells in a developing embryo come from one fertilized egg. Explain how these cells can become muscle, blood, and nerve cells even though they share the same…
All the cells in a developing embryo come from one fertilized egg. Explain how these cells can become muscle, blood, and nerve cells even though they share the same genome. Include the role of gene expression in your explanation.
Scientists studying a frog embryo find that cells close to a certain group of signaling cells become tissue of one type, while cells farther away become another type.…
Scientists studying a frog embryo find that cells close to a certain group of signaling cells become tissue of one type, while cells farther away become another type. Explain how an environmental factor, such as a chemical signal from neighboring cells, can influence which type a cell becomes. Give one other environmental factor that can affect differentiation.
When the cell cycle goes wrong
Normal cells divide only when the body needs them to, for growth or repair. The cell cycle has checkpoints, which are control points that check for problems such as DNA damage before the cell moves on. If damage is found, the cell stops and repairs the DNA, or it self-destructs.
Mutations can break these controls. Mutagens such as UV radiation from sun exposure, tobacco smoke, and some viruses can cause these mutations. If a gene for a checkpoint protein is damaged:
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The checkpoint fails, so the cell divides even with damaged DNA.
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The daughter cells inherit the damage, and more mutations pile up.
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Eventually, the cell divides without normal controls.
Cancer is a disease caused by uncontrolled cell division. A mass of dividing cells is a tumor.
| Benign tumor | Malignant tumor | |
|---|---|---|
| Growth | Stays in one place | Invades nearby tissue |
| Spreads to other body parts? | No | Yes (metastasis) |
| Danger | Usually lower, but can press on organs | Life-threatening if untreated |
Metastasis is the spread of cancer cells through blood or lymph to form new tumors elsewhere.
Name the process in which a cell divides without the normal controls and forms a mass of cells called a tumor. State whether a malignant tumor or a benign tumor can…
Name the process in which a cell divides without the normal controls and forms a mass of cells called a tumor. State whether a malignant tumor or a benign tumor can spread to other parts of the body.
The cell cycle has checkpoints that check for DNA damage before a cell divides. A mutation disables a protein that normally stops the cycle at a checkpoint when DNA is…
The cell cycle has checkpoints that check for DNA damage before a cell divides. A mutation disables a protein that normally stops the cycle at a checkpoint when DNA is damaged. (a) Explain what is likely to happen to cells that carry this mutation and keep dividing with damaged DNA. (b) Explain how this could lead to cancer.
Cancer cells: loss of control and differentiation
Cancer cells differ from normal cells in several ways, and each one connects to the cell cycle or to differentiation:
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Faster, uncontrolled division. A shorter cell cycle and ignored checkpoints.
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No contact inhibition. Normal cells stop dividing when they touch neighbors. Cancer cells pile up.
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Loss of specialization. They look and act less like the specialized cell they came from, so differentiation is disrupted.
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Invasion and metastasis. They move into other tissues.
Different causes (UV radiation, tobacco, some viruses, inherited mutations) lead to the same disease because they all damage genes that control the cell cycle. The immune system normally finds and destroys abnormal cells. Cancer can develop when abnormal cells escape that detection or the immune system is weakened.
A researcher compares two tissue samples from the same patient and records the following. | Feature | Sample A (normal skin) | Sample B (tumor) | |---|---|---| | Time to…
A researcher compares two tissue samples from the same patient and records the following.
| Feature | Sample A (normal skin) | Sample B (tumor) |
|---|---|---|
| Time to complete one cell cycle | 24 hours | 10 hours |
| Cells stop dividing when touching neighbors | Yes | No |
| Cells have specialized shape and function | Yes | Few |
| Cells found in nearby tissues | No | Yes |
Using the data, analyze how Sample B shows disruption of the cell cycle and of differentiation. Explain how each feature in the table relates to the idea that cancer is uncontrolled cell division, and predict whether Sample B is more likely benign or malignant. Justify your prediction.
Sofia reads that some cancers are linked to ultraviolet (UV) radiation and others to certain viruses. Write a claim-evidence-reasoning (CER) response that answers this…
Sofia reads that some cancers are linked to ultraviolet (UV) radiation and others to certain viruses. Write a claim-evidence-reasoning (CER) response that answers this question: How can very different causes lead to the same disease, cancer? Your reasoning should connect mutations in genes that control the cell cycle, loss of normal differentiation, and the role of the immune system in finding and removing abnormal cells.
Back to the start: cells share a genome but differ because of differential gene expression, and cancer happens when mutations break the controls on the cell cycle.
Summary
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Cell differentiation makes specialized cells (neurons, muscle, blood) from unspecialized ones, and structure fits function.
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All cells in an organism share the same genome. They differ in gene expression, which genes are turned on.
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Environmental factors, such as chemical signals from nearby cells or temperature, influence differentiation.
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Checkpoints stop the cell cycle if DNA is damaged. Mutations that disable them allow damaged cells to keep dividing.
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Cancer is uncontrolled cell division. A benign tumor stays put. A malignant tumor invades and spreads (metastasis).
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Cancer cells divide quickly, ignore stop signals, and lose specialization. The immune system helps remove abnormal cells.