2.6.9 Stem Cells

Question 1

Features of Stem Cells

Answer 1

A stem cell is a cell that can divide (by mitosis) an unlimited number of times
Each new cell (produced when a stem cell divides) has the potential to remain a stem cell or develop into a specialised cell such as a blood cell or a muscle cell (by a processes known as differentiation)
This ability of stem cells to differentiate into more specialised cells is known as potency

Question 2

Types of Potency

Answer 2

There are 3 types of potency:
Totipotency - totipotent stem cells are stem cells that can differentiate into any cell type found in an embryo, as well as extra-embryonic cells (the cells that make up the placenta). The zygote formed when a sperm cell fertilises an egg cell is totipotent, as are the embryonic cells up to the 16-cell stage of human embryo development
Pluripotency - pluripotent stem cells are embryonic stem cells that can differentiate into any type of cell found in the embryo but are not able to differentiate into extra-embryonic cells (the cells that make up the placenta)
Multipotency - multipotent stem cells are adult stem cells that have lost some of the potency associated with the embryonic stem cells and are no longer pluripotent

Question 3

Multipotent Adult Stem Cells

Answer 3

As tissues, organs and organ systems develop, cells become more and more specialised
Having differentiated and specialised fulfil particular roles, most adult cells gradually lose the ability to lose the ability to divide, until eventually, they are no longer able to divide
However, small numbers of stem cells (known as adult stem cells) remain to produce new cells for the essential process of growth, cell replacement and tissue repair
Although these adult stem cells can divide (by mitosis) an unlimited number of times, they are only able to produce a limited range of cell types - they are mulitpotent
- for example, the stem cells found in bone marrow are multipotent adult stem cells - they can only differentiate into blood cells (red blood cells, monocytes, neutrophils amend lymphocytes)
- in adults, multipotent stem cells can be found throughout the body (e.g. in the bone marrow, skin, gut, heart and brain)
Research is being carried out on stem cell therapy, which is the introduction of adult stem cells into damaged tissue to treat diseases (e.g. leukaemia) and injury (e.g. skin burns)