Cancer as cell division that has lost its controls one after another: brakes and accelerators, checkpoints that stop damaged DNA, a lump that recruits blood vessels, and the step that turns a benign tumour malignant.
Step 1 of 6 · A lining that renews
Step 1 of 6
A lining that renews
The lining of the gut is replaced every few days: stem cells deep inside it keep dividing by mitosis, and their offspring rise, work and are shed. The tissue keeps the same thickness all through life because every cell obeys controls: it divides only when a cell is needed, stops when told, and checks its DNA before every division. At Healthy the lining is one layer of tall cells on a thin sheet, the basement membrane.
The controls are proteins, and each protein is built from a gene. Some genes act as an accelerator, passing on a signal to divide; when a mutation leaves one stuck on it is called an oncogene. Others act as a brake: they are tumour suppressor genes. Remember that every body cell has two copies of each gene, one from each parent.
Step 2 of 6
Checkpoints
Checkpoints are moments in the cell cycle when the cell stops and checks itself. If the DNA is damaged, a protein called p53 halts the cycle until the damage is repaired, and if it cannot be, makes the cell destroy itself, apoptosis. Show the checkpoints is On, and Mutations at Polyp: amber cells are held at a checkpoint, and brown fragments are cells that destroyed themselves.
Step 3 of 6
The lump
A lump needs food and oxygen, and they seep only a millimetre or two from the nearest blood vessel. At Lump, new blood vessels sprout into it, and with a blood supply of its own it can reach about a billion cells. And all those cells are the offspring of one cell, doubling their number again and again.
Step 4 of 6
Benign or malignant
So far the lump is a benign tumour: however big it gets, its cells stay on their own side of the basement membrane. Look at the cut through the front of the lump, and predict what the fifth mutation changes.
Step 5 of 6
Years in the making
Every division leaves a few new errors in the DNA, and sunlight and tobacco smoke add more. A mutation that breaks a control gives its cell a small advantage, and its offspring, a clone, slowly spread. Within the clone another mutation breaks another control, and so on. This is natural selection inside the body. Move Mutations step by step from to and follow the clone’s size on the chart.
Step 6 of 6
Stopping division
A tumour that has not spread can often be removed by surgery. A cancer that has spread, as at Spreading, needs drugs that reach the whole body. Many of them kill dividing cells, for instance by jamming the spindle that pulls the chromosomes apart in mitosis.
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Each step sets up the Scene for you, and a control marked “fixed” stays put for that step.
Practice · Choose
Every cell has two copies of each gene. Why can one mutation in an accelerator gene already push the cell to divide, while a brake gene usually needs both copies broken?
Practice · Choose
Every cell has two copies of each gene. Why can one mutation in an accelerator gene already push the cell to divide, while a brake gene usually needs both copies broken?
Practice · Predict, then look
In the polyp, two mutations, many cells whose DNA was damaged are amber: held at a checkpoint. The third mutation breaks the p53 checkpoint. Predict what you will see when Mutations goes up to .
Practice · Predict, then look
In the polyp, two mutations, many cells whose DNA was damaged are amber: held at a checkpoint. The third mutation breaks the p53 checkpoint. Predict what you will see when Mutations goes up to .
Practice · Calculate
A lump of about a billion cells, , started from one cell whose offspring all kept dividing. How many doublings of the number of cells does it take to get from one cell to a billion?
Practice · Calculate
A lump of about a billion cells, , started from one cell whose offspring all kept dividing. How many doublings of the number of cells does it take to get from one cell to a billion?
Practice · Predict, then look
The lump, four mutations, is already a centimetre across with its own blood vessels, and it is still benign. Predict what the fifth mutation changes, the one that makes it malignant.
Practice · Predict, then look
The lump, four mutations, is already a centimetre across with its own blood vessels, and it is still benign. Predict what the fifth mutation changes, the one that makes it malignant.
Practice · Choose
Why do most cancers appear in older people?
Practice · Choose
Why do most cancers appear in older people?
Practice · Choose
Many chemotherapy drugs jam the mitotic spindle and kill dividing cells. Why do they often cause hair loss and digestive trouble?
Practice · Choose
Many chemotherapy drugs jam the mitotic spindle and kill dividing cells. Why do they often cause hair loss and digestive trouble?
Lesson complete. Every practice question here is done.