section 11.4 cell differentiation · defining differentiation •differentiation- the process by...
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Section 11.4Cell Differentiation
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Standard
• ETS2.3 Analyze scientific and ethical arguments to support the pros and cons of application of a specific biotechnology technique such as stem cell usage, in vitro fertilization, or genetically modified organisms.
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I Can…
• ETS 2.3 I can conduct an ethical argument to support the pros and cons of specific biotechnology techniques (stem cell usage, in vitro fertilization, or GMOs).
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Key Questions
1. How do cells become specialized for different functions?
2. What are stem cells?
3. What are some possible benefits and issues associated with stem cell research?
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Vocabulary
• Embryo
• Differentiation
• Totipotent
• Blastocyst
• Pluripotent
• Stem cell
• Multipotent
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Cell Differentiation
• Why do some cells turn into muscle cells, some into nerve cells, others into bone and skin cells, etc.?
• Animals and higher plants pass through a developmental stage called an embryo, from which the adult organism is gradually produced.
• During this process, cells become specialized for different functions.
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Defining Differentiation
• During the development of an organism, cells differentiate into many distinct cell types.
• Differentiation- the process by which cells become specialized
• A differentiated cell has become different from the embryonic cell that produced it and specialized to perform certain tasks.
• The bodies of multicellular organisms contain highly differentiated cells that carry out functions for us to stay alive.
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Human smooth muscle cells Human nerve cells Human red blood cells
Leaf tissue Root tissues Cross-section of a stem
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Mapping Differentiation
• In some organisms, a cell’s role is rigidly determined at a specific point in the course of development.
• Example- C. elegans (a microscopic worm) • Biologists have mapped out every cell division from fertilized egg to adult
• Adults contain exactly 959 cells with precise functions
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C. elegans example
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Differentiation in Mammals
• Other organisms, including mammals, go through a more flexible process.
• Cell differentiation is controlled by a number of interacting factors in the embryo • Many are still not well understood
• We do know that adult cells reach a point at which differentiation is complete (they can no longer turn into other types of cells)
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Stem Cells and Development
• Stem cells are the unspecialized cells from which specialized cells develop.
• All specialized, differentiated cell types in the body are formed from a single cell, the fertilized egg (zygote)
• Totipotent- cells that can develop into any type of cell in the body (including the cells that make u the extra-embryonic membranes and placenta) • only the zygote and cells after the first few cell divisions of embryonic
development are truly totipotent
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Stem Cells and Development
• After 4 days of development, a human embryo forms into a blastocyst• A hollow ball of cells with a cluster of cells inside (inner cell mass)
• The outer cells form tissues that will attach the embryo to its mother
• The inner cell mass becomes the embryo itself
• The cells of the inner cell mass are pluripotent• Cells that are capable of developing into any of the body’s cell
types (but not the tissue surrounding the embryo)
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Embryonic Stem Cells
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Adult Stem Cells
• Multipotent- stem cells that can differentiate to replace cells in tissues where they are found
• Examples:• New blood cells differentiate from stem cells
found in bone marrow
• Many skin stem cells are found in hair follicles
• Small clusters have been found in the brain, heart, and skeletal muscle
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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.
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Induced Pluripotent Stem Cells (iPS cells)
• 2007- Dr. Shinya Yamanaka of Kyoto University in Japan
• Converted fibroblast cells into cells that resembled embryonic stem cells
• Maybe under the right conditions, these iPS cells could replace embryonic stem cells?
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Induced Pluripotent Stem Cells
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Regenerative Medicine
• Makes use of stem cells to replace damaged cells or tissues
• Now in clinical trial- using stem cells to treat macular degeneration• Results in loss of vision• Experimental treatments take
stem cells from the patient’s body and convert them to iPS cells
• These cells were stimulated to differentiate into cells of the eye
• Risks• Could differentiate into unwanted
cell types• Could spread beyond the site of
the transplant• Could grow uncontrollably into a
tumor
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Future Treatment?
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Section 11.4 Exit Ticket
1. What happens during differentiation?
2. What are stem cells?
3. What are the arguments for and against the use of stem cells in medical research?
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The End