Cancer | Cells | MCAT | Khan Academy

Main Ideas

• Normal cell growth is regulated. Cells divide by mitosis to support growth and replace dead cells. They generally respond to nearby cells by slowing or stopping growth, a process called contact inhibition.
• Damaged cells can self-destruct. When a cell detects serious damage, it may undergo apoptosis, a programmed process in which the cell destroys itself. This helps prevent defective cells from multiplying.
• Most body-cell mutations are not inherited by offspring. Mutations in somatic cells (body cells) can affect the person or tissue but are not passed on through reproduction.
• The scale of cell division creates opportunities for errors. The presenter estimates that the body makes roughly 100 billion new cells per day and contains about 100 trillion cells. Even uncommon replication errors can therefore occur many times, though many have no effect or are dealt with by the cell.

How Abnormal Growth Can Develop

1. A cell acquires mutations in its DNA.
2. Some mutations may prevent apoptosis or cause the cell to divide faster than its neighbors.
3. The abnormal cell produces descendants that inherit its faulty DNA.
4. A mass of abnormal tissue may form. The video calls this a neoplasm; if it forms a noticeable lump, it is commonly called a tumor.
5. If the growth remains localized and does not significantly harm nearby tissue, it is described as benign.
6. Further changes may make the cells grow aggressively and invade surrounding tissue.
7. If cells break away and spread to other parts of the body, the process is called metastasis.

• Cancer involves abnormal, uncontrolled growth and can spread. Cancer cells may fail to respect contact inhibition, crowd out healthy cells, compete for resources, invade nearby tissue, and metastasize.
• Cancer is not one single disease. It encompasses many different patterns of mutations. Because cancer cells can continue to accumulate changes, a treatment may eliminate some cells while resistant variants survive and become harder to treat.
• Treatment approaches target shared features. The presenter notes that chemotherapy and radiation often target rapidly growing cells, a feature common to many cancers. The central lesson is that cancer can arise when DNA replication and the safeguards that normally control damaged cells fail.

Speakers and Sources

• Sal Khan — presenter and narrator, speaking on behalf of Khan Academy.