Cell Differentiation=Cell Specialization

Lesson Essential Question For today’s lesson we have one main question to answer: Why is Cell Differentiation an important part of the development of a multicellular organism?

Topics for Discussion: 1. What is cell differentiation? 2. How are stem cells related to differentiation? 3. What makes a cell a stem cell? 4. What are 2 main types of stem cells? 5. Identify misconceptions about stem cell research.

What is Cell Differentiation? Cell Differentiation=Cell Specialization It is a process. And in this process, a cell becomes “specialized” for a specific structure or function during multicellular development.

Why is cell differentiation directly related to STEM CELLS? Well, stem cells are the ones able to differentiate Stem cells are unique cells. They have several abilities: 1. The can divide and renew themselves for long periods of time. 2. They can remain undifferentiated in form. 3. They can develop into another type of cell (differentiate).

Pause and Connect: Take a minute and examine this diagram. In your notebook write one sentence describing what this diagram tells you as a biologist.

What, then, makes a blood cell different from a skin or muscle cell, or a leaf cell from a root cell in a plant?

The answer lies in the way each cell “deploys” or utilizes its genome. In other words, the particular combination of genes that are turned on (expressed) or turned off (repressed) dictates cellular structure and function.

What does this mean exactly? And How does it happen? All of the cells within a complex multicellular organism, such as a human being, contain the same DNA. Correct? BUT, each cell expresses this DNA differently. Actually, a cell’s location within the embryo helps determine how it will differentiate.

First, it is decided which genetic information will be expressed, thereby indicating the type of cell that is to be formed. Then, through cell differentiation, those instructions are carried out and specialized cells are formed.

Thus, different cells can have very different physical characteristics despite having the same genome.

Think about this process as DNA being a cookbook…. When you want to make a specific dish, you select that recipe from the cookbook and carry out its instructions…. The same way, cells only express specific genes it needs to carry its function.

When does differentiation occur? Differentiation occurs numerous times during the development of a multicellular organism. As the organism changes from a simple zygote to a complex system of tissues and cell types. Differentiation is a common process in adults as well: adult stem cells divide and create fully differentiated daughter cells during tissue repair and during normal cell turnover.

Let’s Describe Major Types of Stem Cells: Embryonic Stem Cells Totipotent: cell can develop into all cell types. Can self-renew indefinitely Plentiful Embryos used in research is 4-5 days old: it is a ball of cells Left over embryos from IVF procedures. They are mostly donated. Adult Stem Cells Multipotent: cell can develop into a few cell types but not all. Hard to find. Body cells (somatic) found in organs and tissues. They are called “adult” because they are found after an embryo develops into a fetus and are no longer an embryonic stem cell.

Examples of Specialized Cells- blood cells ◦ Red blood cells carry Oxygen to body cells. ◦ White blood cells protect us from infection by attacking foreign substances. White blood cell Red blood cells

Muscle Cells Muscle cells are specifically designed to contract, to cause movement. Their long, cylindrical shape is perfect for contracting.

Epithelial Cells Epithelial cells are found on biological surfaces. They can be designed for protection, absorption, secretion, etc.

In Plants: Specialized “hair cells” on roots are designed to increase absorption of water and nutrients, through increased surface area. Other cells in roots are designed for growth, and protection.

Plant stems have cells that are specialized for transporting water, nutrients, etc. throughout the plants.

Leaves of plants have many kinds of specialized cells. Guard cells open and close to let out water vapor and allow for gas exchange. Palisade cells have many chloroplasts for carrying out photosynthesis.

Putting it all together…. In all previous examples, the particular combination of genes that are turned on (expressed) or turned off (repressed) has dictated or determined: 1. How these cells work 2. And what they look like…

Stem Cell Debate and Misconceptions Many people oppose stem cell research as they believe that the 4-5 day old embryo is a living human being. What some do not understand is that unused embryos are discarded regardless. Some believe it is better to use these embryos for research on how to cure human diseases rather than discarding them away without purpose.

Misconceptions Pregnancy, fetuses or babies are aborted or harmed in stem cell research. Fertilized Blastocysts donated from IVF labs are used and no pregnancy is aborted. The fertilized embryos are removed from women’s bodies and used for research. The embryos are left over from IVF and are frozen and are not implanted for pregnancy.

Misconceptions A clone is grown in a lab without an embryo or born from a mother and is the same age and personality as you, and has no belly button. A clone would need a fertilized embryo and would have to be implanted in a woman’s uterus. If you were cloned at 14, the clone would be 14 years younger than you (a baby you) and would have to have a mother to be born, so yes, it would have a belly button.

Misconceptions If the embryos were not used in stem cell research they would have been used to make children. The embryos left over from IVF are discarded. Men and women who donate their embryos do not know that their embryos are used for research. The embryos used in scientific research are donated with written and informed consent (permission) by the donors.

Lesson Essential Question To answer our essential question: Why is Cell Differentiation an important part of the development of a multicellular organism? It is essential because one kind of cell cannot perform all the activities required for life.