17) Stem Cells Summary_9744_2019

The Cell and Biomolecules of Life (9744) Stem Cells 2019 Prepared by: Mrs. Selvamani Nair and Mr Low Chor Meng Raffles Institution 1 Stems Cells a) are unspecialized/undifferentiated i.e. they do not have any tissue-specific structure for it to perform a particular function b) are able to differentiate to produce specialised cells upon receiving appropriate molecular signals (e.g. hormones, growth factors) c) undergo extensive proliferation and self-renewal i.e. they can divide many times by mitosis, with the daughter cells possessing the same developmental and replicative potential as the parent cell d) can undergo 1) symmetrical division  produces 2 identical daughter stem cells to ensure a constant pool of stem cells 2) asymmetrical divisionproduces a) 1 daughter stem cell  to ensure a constant pool of stem cells & b) 1 progenitor cell to replace a population of specialised cells in a specific tissue that died occurs in the presence of appropriate molecular signals e) can be 1) totipotent  can differentiate into all of the cell types that make up an entire organism including the extraembryonic tissue e.g. the placenta  e.g. fertilised egg to 8 cell stage (These cells are zygotic stem cells.) 2) pluripotent  can differentiate into all of the cell types that make up an organism except the extraembryonic tissue such as the placenta  e.g. inner cell mass of blastocyst (The cells in the inner cell mass are embryonic stem cells.) 3) multipotent  can develop into only a limited and related range of cell types and tissues in an organism  e.g. haematopoietic stem cells, which are found in the bone marrow & give rise to all of the cells found in the blood, including red blood cells, white blood cells, and platelets. Haematopoietic stem cells are adult stem cells. They are also found in babies.) Note: 1) Stem cells can differentiate into different cell types due to the presence of molecular signals that cause differential switching on of genes. 2) A progenitor cell is an early descendent of a stem cell that can only differentiate. It cannot renew itself. e.g. lymphoid progenitor cells gives rise to B cells, T cells and natural killer cells while myeloid progenitor cells give rise to red blood cells, monocytes, platelet producing cells, neutrophils, basophils and eosinophils 3) Stems cells can continue to divide mitotically