干细胞研究 Stem Cells in Biology.ppt

Objectives Define and describe the characteristics of embryonic and adult stem cells Describe the origins of various stem cells Describe the debate surrounding and identify misconceptions about stem cell research Describe the present and future applications for stem cell research What makes a cell a stem cell? Plasticity: A stem cell is plastic, meaning it can develop into another type of cell. Differentiation: The process where a stem cell specializes or develops into another type of cell. Self-Renewal: a stem cell can divide (renew itself) indefinitely (go through mitosis) and without always developing into another cell. Differentiation Major Types of Stem Cells Embryonic Stem Cells Totipotent : cell can develop into all cell types “Immortal”: can self-renew indefinitely Plentiful Adult Stem Cells Multipotent: cell can develop into a few cell types but not all Located in few organs or may be unidentified Hard to find Embryonic Stem cells Embryos are formed in labs that help couples get pregnant. An egg and sperm fertilize a zygote and are inserted into a woman’s uterus to develop into an embryo and then fetus. In Vitro Fertilization (IVF): a sperm fertilizes an egg in a lab dish creating the embryo. Embryonic Stem Cells This process creates multiple embryos that will not be used to make a baby. Many donors wish to donate these unused embryos to scientific research instead of having the lab throw them away. Embryonic Stem Cells The embryo used in research is 4-5 days old and is a microscopic ball of about 150 cells. The ball as thick as a hair is called a Blastocyst and has three layers called germ layers. Each layer has special stem cells that makes a part of the body. Blastocyst: Source of Embryonic Stem Cells Germ Layers The embryo develops three germ layers of cells called the ectoderm, mesoderm and endoderm Embryonic Stem Cell These embryos not used in IVF will not grow into a fetus or baby because an embryo like the