Cell SpecializationRemember . . . . .• All living things are made of cells!!!

• Cells can specialize into different cell types Cells tissues organs

• These cells, tissues, and organs make up the systems of an organism

How do cells know what job they have to do? What tissue they will belong to?

How do cells become specialized?

Stem CellsStem cells – unspecialized cells that can differentiate into a

variety of specialized cells • Embryonic stem cells • Adult (tissue) stem cells

Differentiation – process of converting stem cells into more specialized cell

• Cells have specific structure and function• Occurs when a zygote becomes an organism• For tissue repair• Normal cell renewal (self-renewal)• Ex. liver cell, blood cell, nervous cell,Muscle cells, bone cell

Stem Cell Vocabulary and DevelopmentTotipotent – fertilized egg or first few cells in an embryo that are able to form any kind cell and tissue

Pluripotent – cells in the embryonic blastocyst (hollow ball of cells) stage can become any type of body cell

Multipotent – adult stem cells that can produce certain differentiated cells

A stem cell that can:• Become any type of cell in the body is pluripotent• Become only a few type of cells is multipotent

Why are Stem Cells so Special?When a stem cell divides, it can either:• Self-renew – make more stem cells• Specialize and make other cell types

Embryonic stem cells – cells harvested from an embryo (blastocyst stage)

• Can become any cell type• Can reproduce indefinitely• Usually created from in vitro fertilization

• ControversialType of stem cell

Adult stem cell - can renew itself and can differentiate to yield some or all of the major specialized cell types of the tissue or organ they came from

• maintain and repair the tissue in which they are found• Have been used for blood-forming• stem cells from bone marrow have been used in

transplants for more than 40 years• Scientists now have evidence that stem cells exist in

the brain and the heart, two locations where adult stem cells were not at first expected to reside.

If the differentiation of adult stem cells can be controlled in the laboratory, these cells may become the basis of transplantation-based therapies.

All cells contain the exact same DNA (all 46 chromosomes), but not all cells look the same nor have the same job

Different proteins are madeby different cells causing them to look and functiondifferently• Called gene expression• Controlled by signals received from control genes,

enhancers, or promoter genes “turning on” certain sequences of DNA (a gene)