Standard B-2.4 : Explain the process of cell differentiation for the hierarchical organization of organisms (including cells, tissues, organs, and organ systems)

Key Concepts Cell Division Differentiation Stem Cells

It is essential for you to know: In the development of most multicellular organisms, a single cell (fertilized egg) gives rise to many different types of cells, each with a different structure and corresponding function. Nearly all of the cells of a multicellular organism have exactly the same chromosomes and DNA. Stem cells are unspecialized cells that continually reproduce themselves and have, under appropriate conditions, the ability to differentiate into one or more types of specialized cells.

Objectives Explain the process of cell differentiation. Recall that all of the cells of a particular organism contain all of the genetic code. Summarize the unique characteristics of embryonic and adult stem cells.

Vocabulary Words Define the following vocabulary words: Tissue Organ Organ system Cell differentiation Stem cell

Let’s start with a video Cell Specialization

Each of us enters this world as a screaming infant Each of us enters this world as a screaming infant. At first, the ability to eat solid foods of take a step draws forth great praise. These general skills rapidly lose their wonder, however, and by the time you reach the age of 18, everyone wants to know what you plan to do with yourself. Will you build houses or design clothing or treat patients? What will your specialty be? Cell, too, undergo specialization to carry out the complex functions required by the body.

Life Begins All life starts with a single cell, a fertilized egg or zygote.

Differentiation The fertilized egg gives rise to many different types of cells in a multicellular organism. Each cell has a particular structure and function. This is called differentiation. The DNA of each cell serves as the blueprint for the entire organism. The organism grows by repeated cell division. Although nearly every nucleus has the same genetic information, each cell uses only the portion of that information that it needs. During differentiation, cells begin to “read” different parts of the DNA and ignore other parts. Think about this: if you wanted to look up the word differentiate in the dictionary you would go straight to the D section. You would not look up other words that start with other letters. Even though that information is there, it is not needed right now. The same thing happens with cell differentiation.

How? Cell division gives rise to many cells. It does not explain how each cell is specialized. As the cell continues to divide, it not only increases in number but also begin to differentiate, meaning they become specialized in structure and function. These cells organize themselves into tissues, then organs, and organ systems. How cells differentiate partly depends on their physical location within the organism and partly on communication with other cells. Cells produce chemicals that tell other cells what they are doing. These chemical signals coordinate the specialization of cells to form the body plan coded for in the DNA. By following the specific sections of this code, cells take on specific shapes and functions.

Red blood cells have to be round and raft-shaped to transport oxygen around the body. Neurons or nerve cells have to be long and thin to carry messages around the body. Skin cells have to be broad and flat, like tiles to help them cover the surface of the human body without adding thickness. Cells come in many different shapes and sizes each with their own particular structure and function.

Not so fast, though. Even though cells are differentiated, they contain the same DNA in their nucleus. During the process of specialization only parts of that DNA are activated. This activated part determines the structure and specialized function. Since they all have the same DNA, they have the potential to become any type of cell. However, once a cell specializes it cannot be reversed.

Stem Cells There is one type of cell that is unspecialized and can continually reproduce under the right conditions. They are called stem cells. They have the ability to divide and renew themselves for long periods of time, remain undifferentiated in form, and develop into a variety of specialized cells.

Stem Cells

Stem Cells

Stem Cells

Stem Cell Classification Potential Origin Totipotent Can grow into any type of cell Only the fertilized egg and cells produced by the first few divisions of an embryo. Pluripotent Can grow into any cell type except totipotent Multipotent Can only grow into cells of a closely related family Embryonic Stem Cells Found in embryos Can give rise to any type of cell Very controversial Adult Stem Cells - Found in human adults - Bone marrow can give rise to blood or bone cells. Not as controversial

Stem Cells Embryonic Stem Cells Adult Stem Cells