Stem Cells: Same DNA, Different Genes Switched On

0:00Your blood holds several kinds of cells. Where do new ones come from?

0:05They are made in bone marrow, the soft tissue inside many bones.

0:10Bone marrow holds stem cells. A stem cell is unspecialized: it has no particular job yet.

0:18It can divide again and again. Some new cells stay stem cells, and others specialize.

0:25Bone marrow stem cells make red blood cells, white blood cells and platelets.

0:31Each is specialized, with a structure that suits its job: carrying oxygen, fighting infection, or helping blood clot.

0:40Becoming specialized like this is called differentiation.

0:44Your bone marrow makes billions of new blood cells every day.

0:49Bone marrow transplants use these stem cells to treat some blood cancers.

0:55So does a specialized cell have different DNA from its stem cell?

1:00No. When a cell divides, each new cell gets an exact copy of the same DNA.

1:07DNA carries many genes. A gene is a section of DNA that codes for a particular protein.

1:14Becoming specialized means switching some genes on and others off.

1:20The genes that are on decide which proteins the cell makes, and so its structure and job.

1:27Plants have stem cells too. At the growing tip of a root, they make up a tissue called meristem.

1:34Meristem cells keep dividing, and the new cells switch on different genes to become, for example, root hair cells.

1:43Stem cells make specialized cells by switching genes on and off, not by changing their DNA.