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Bio errata
This text on the bottom of p.558 and the top of p.559 (MCAT Biology and Biochemistry
Review) and pages 482-483 in MCAT Complete :
“Primitive cells in an early embryo have the potential to become any cell type. They are known
as totipotent cells. As development continues, the cells begin to specialize somewhat
(gastrulation). Cells from the early embryonic germ layers are described as pluripotent. These
stem cells have the ability to become many different mature cell types.
Stem cells, because of their ability to become nearly any cell type in the body, are of great
interest in research; they remain a potential source for regenerative medicine and tissue
replacement after injury or disease.”
Should be replaced with this:
“Primitive cells in the zygote and the morula have the potential to become any cell type in the
blastocyst, including the trophoblast and the inner cell mass. They are therefore known as
totipotent cells. Cells of the inner cell mass are more specialized and are called pluripotent.
They can differentiate into any of the three primary germ layers (ectoderm, mesoderm or
endoderm) and therefore have the capability to become any of the 220 cells types that make up
an adult human. However, they cannot contribute to the trophoblast of the blastocyst.
As development continues, cells continue to specialize. For example, after gastrulation, cells
from the early embryonic germ layers are each considered multipotent. This means they can
become many, but not all cell types. For example, cells of the mesoderm can differentiate into
muscle and bone cells, but not into neurons or digestive epithelium.
In other words, totipotent cells differentiate into pluripotent cells, which specialize to become
multipotent cells. Most cells in the adult have lost all potency and have become completely
specialized mature cells, incapable of changing into other cell types. Adult stem cells are an
exception to this, and these cells are discussed in section A.13 of Appendix 1.
Stem cells, because of their ability to become nearly any cell type in the body, are of great
interest in research; they remain a potential source for regenerative medicine and tissue
replacement after injury or disease. In humans, embryonic stem cells are the only pluripotent
cells that have been found. These cells are isolated from the inner cell mass of the blastocyst.”
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Term
Definition
Totipotent
• Can generate trophoblast and inner
cell mass
• zygote
• morula
• iPS cells
Pluripotent
• Can differentiate into any of three
primary germ layers
• Can generate all adult cell types
(over 220)
• inner cell mass of blastocyst
(embryonic stem cells)
Multipotent
• Can produce many (not all) cell types
• More differentiated than pluripotent
• Often tissue-specific
• 3 primary germ layers
• Adult Stem Cells
• Some cells can go backwards
• Example: Mature  Multipotent 
Pluripotent  Totipotent
• iPS cells
• cancer cells
Dedifferentiation
Examples
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