Monday, December 5th Miss Brawley

Do Now: Begin workbook pages 153-155

Stem cells are undifferentiated cells

Stem Cells Stem cells have two important characteristics: They are unspecialized cells that are capable of renewing themselves by cell division. Under certain natural or experimental conditions they have the ability to differentiate into one or more types of specialized cells.

Animal Stem Cells Human embryonic stem cells are derived from a 5-day old embryo. They have the capacity for long-term self- renewal in laboratory culture. They can develop into any type of specialized cell in the body.

Stem Cells Totipotent: can develop into any type of cell in the body (including the cells that make up the extraembryonic membranes and placenta) Pluripotent: cells that are capable of developing into most, but not all, of the body’s cell types Explain that the original, unspecialized cells from which all cell types arise are called stem cells. Point out that how all possible cell types arise from a single cell—the zygote—is one the most important questions in biology! Ask a volunteer to come to the board to write in the term that completes the sentence. Click to reveal the correct answer. Explain that scientists use the term totipotent to describe the zygote. The term literally means “can do everything.” These cells can become any cell or tissue type anywhere in the body. The only cells in the developing organism that are truly totipotent are the original one-celled zygote and those cells produced by the first few cell divisions. Click to reveal the totipotent definition. Click to reveal the definition of pluripotent. The cells of the inner cell mass are described as “pluripotent”—they become almost any cell or tissue type, except for those tissues that will surround the embryo.

Animal Stem Cells Adult stem cells are undifferentiated cells found in certain organs and differentiated tissues with a limited capacity for both self renewal (in the laboratory) and differentiation.

Adult Stem Cells Mainly found in bone marrow, hair follicles Multipotent: limited potential to develop into many different types of differentiated cells Mainly found in bone marrow, hair follicles Also some in brain, heart, and skeletal muscle Emphasize that it makes sense to find stem cells in the early stages of embryonic development, but stem cells can in fact also be found in an adult’s body. Ask students if they have heard anything about adult stem cells in news reports. Point out that while the adult body does have stem cells, these cells are neither totipotent nor pluripotent. Instead, they are described as multipotent. Click to reveal the definition of multipotent. Click to reveal each of the remaining bullet points as you explain the following. Explain that there are several regions in the adult body where stem cells are found. These stem cells give rise to a limited variety of cell types, mainly those found in tissues where the stem cells are produced. These adult stem cells produce cells for tissues such as blood and skin that have a limited life span and must be constantly replaced. Share with students that bone marrow transplants, which they may have heard about, are effectively stem cell transplants. Hematopoietic cells differentiate into white blood cells, red blood cells, and platelets. Bone marrow transplants can be used to treat patients with certain blood disorders that cause the patients to produce abnormal blood cells. Bone marrow transplants can also be used to treat cancer patients whose own marrow has been damaged by high doses of chemotherapy or radiation.

Stem Cells Stem cells are important to the living organism. In 3-5 day old animal embryos they give rise to the entire body of the organism, including all of the many specialized cell types and organs such as the heart, lungs, skin, sperm, eggs, and all other tissues. In some adult animal tissues, such as bone marrow, groups of stem cells generate replacements for cells that are lost through normal wear and tear, injury, and disease.

Stem Cells Importance uses of stem cell research and biotechnical applications: Scientists use stem cells to study normal growth, development, and differentiation. This research can help to identify the causes of cancer and birth defects that result from abnormal development. Stem cells are currently used to screen new medicines for safety in humans. Cell-based regenerative therapies are treatments in which stem cells are induced to differentiate into specific cell types required to repair damaged or destroyed cells or tissues.

Stem Cells Cell-based regenerative therapies use: The demand for organs and tissues needed for transplantation is greater than the supply. Stem cells offer a renewable source of replacement cells and tissues such as: bone tissue from bone marrow cells, spinal cord after injury cells of the pancreas that produce insulin to treat diabetes.

Regenerative Medicine Explain that bone marrow transplants are just one type of stem cell therapy researchers have worked on. Researchers are looking for ways to repair damage to heart muscle from heart attacks, destruction of brain cells from strokes, and damage to nerve cells from spinal cord injuries. The diagram here shows one method currently being investigated to reverse the damage caused by a severe heart attack. Read through the steps shown in the diagram. Ask: Are the cells being transferred pluripotent or multipotent? How do you know? Answer: Multipotent; they are from adult tissues, not from an embryo in early stages of development. Ask: How would the fate of the stem cells change after they are moved from the bone marrow to the heart? Answer: They would become heart muscles rather than blood cells. Point out that similar techniques might be used to treat brain damage, regenerate nerves, or repair organs such as the liver and kidneys that have been damaged by chemicals or disease. Undifferentiated cells are used to repair or replace damaged cells and tissues.

Stem Cells Pros/cons of human embryonic and adult stem cells for cell-based therapies? Make a T-chart or venn diagram to compare the two possibilites!

Stem Cells Pros/cons of human embryonic and adult stem cells for cell-based therapies: The number of types of cells they can become: Embryonic stem cells can become all of the types of cells in the body. Adult stem cells are thought to be limited to the types of cells in the tissue of origin.

Stem Cells Pros and cons: Ease of growth in laboratory culture. Embryonic stem cells can be easily grown in culture and can divide indefinitely producing large numbers of cells for research. Adult stem cells are difficult to isolate from the original tissue and are difficult to grow in culture.

Stem Cells Pros and cons: Potential for rejection by the human immune system. It is unknown how the immune system might react to embryonic stem cells. Scientists think that adult stem cells are less likely to be rejected by the immune system because a patient’s own cells can be used.

Ethical Issues Human adult stem cell research is rarely controversial because of willing donors. Human embryonic stem cell research is controversial because arguments for and against involve ethical issues of life and death. Ask students why research into therapies using adult stem cells is less controversial than research into therapies involving embryonic stem cells. Encourage them to consider how the issue of donor consent might play a role. Also guide them to see that both sides of the controversy over embryonic stem cell use are making an ethical case: Those arguing for using embryonic stem cells argue that not using the cells would prevent doctors researchers from saving lives, while many arguing against the use of these stem cells argue that they are protecting human embryonic life. To bring the discussion to a close, click to reveal the full statements for each bullet point.

Plant Stem Cells Virtually all of a plant’s tissues are descended from small groups of stem cells located in the actively growing tips of the roots and shoots. Plant stem cells have the capacity to grow into any type of plant organ, tissue, or cell.

Plant Stem Cells Plant stem cells have the capacity for nearly unlimited self-renewal. Many important compounds are derived from plants such as medicines, pigments, perfumes, and insecticides. Stem cell technology offers the potential to produce these chemicals under controlled conditions.

Class Work/ Home Work Workbook 10.4 Pages 153-155 Quiz 10.4

Cellular Reprogramming Induced Pluripotent Stem Cells (iPS cells) May ultimately help society reframe the debate over use of stem cells Identify the scientist in the photo as researcher Shinya Yamanaka. Describe how in 2007 he was able to convert human fibroblast cells (cells that produce components of the body’s connective tissues) into cells that closely resemble embryonic stem cells. These cells are called induced pluripotent stem cells. Click to reveal the first bullet point. These cells may ultimately make it possible to tailor specific therapies to an individual by using that person’s own cells. Click to reveal the second bullet point. Ask students how these breakthroughs affect the debate over stem cell use. Lead a brief discussion about the possibilities. Be sure students come away from discussion with the understanding that further work on iPS cells may ultimately solve the ethical problems that have made stem cell research controversial. Dr. Shinya Yamanaka

Stem Cell Video

Video Quiz What disease did the boy at the beginning of the video have? What type of cells did all three scientists turn into stem cells? What was the problem that occurred in mice and other test subjects that the stem cells were injected into?