Section 11.4Cell Differentiation

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.

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).

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?

Vocabulary

• Embryo

• Differentiation

• Totipotent

• Blastocyst

• Pluripotent

• Stem cell

• Multipotent

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.

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.

Human smooth muscle cells Human nerve cells Human red blood cells

Leaf tissue Root tissues Cross-section of a stem

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

C. elegans example

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)

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

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)

Embryonic Stem Cells

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

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.

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?

Induced Pluripotent Stem Cells

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

Future Treatment?

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?

The End