What are stem cells ?

Characteristics that distinguish stem cells from other cells 1.They are undifferentiated cells (their job is to become special cells when needed) 2.They can be grown continuously in a culture (stem cell line) 3.They can be changed (using chemicals) to become cells with special functions

Why the name “stem cells”

Differentiation When a cell becomes a special cell type What controls differentiation? Chemicals released by other cells The location of the cells (the stem cell niche)

Day 14 still the size of a pencil tip Cells in the blastocyst migrate to form three layers of cells. Each of these layers are stem cells, but can only become certain types of cells. These cells have begun to differentiate.

All cells have the same genes (information) However, eye cells differ from nose cells So how do they become different?

Gene Activation: As a cell differentiates, some genes are turned on and some are turned off Only the genes necessary to make the type of cell needed will be working. Like a computer with all information, but only certain programs are turned on, others are off

Cells in the embryo continue to migrate and differentiate. The brain and spinal cord begin to form Days

4 weeks 1/6 inch By 4 weeks the heart is beating. Cells are still differentiating.

5 weeks 1/6 inch

6-8 weeks ½ inch

12-16 Weeks 2.5 inches ½ ounce

Two basic types of stem cells: 1.Embryonic stem cells (ESC)- obtained from fertilized eggs left over from in vitro fertilization (IVF). Collected from the inner cell mass (ICM) Original 30 cells yield millions of embryonic stem cells Batches of them can be frozen and shipped to other laboratories

ESC’s approx. 30 cells Scientists have "recipes" of chemicals for the differentiating ESC ’ s into specific cell types

2.Adult stem cells (ASC) - both children and adults have them in specific areas (niche) The cells divide and differentiate when needed One cell always remains a stem cell

Why is this so controversial? Invitro-fertilization is the process of bringing gametes together to form a zygote in a petri dish and letting them develop into blastocysts. The blastocysts are either frozen for later or put inside a women in order to cause pregnancy

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