Totipotent Cells (AQA A Level Biology)

Totipotent Cells

• A stem cell is a cell that can divide (by mitosis) an unlimited number of times

• Each new cell that is produced when a stem cell divides has the potential to remain a stem cell or to develop into a specialised cell such as a blood cell or a muscle cell (by a process known as differentiation)

• This ability of stem cells to differentiate into more specialised cell types is known as potency

• There are three types of potency:

  • Totipotency

  • Pluripotency

  • Multipotency

Totipotent Stem Cells

• Totipotent cells can divide and produce any type of body cell

• This type of stem cell is also referred to as 'embryonic stem cells

• Totipotent cells exist for a limited time in early mammalian embryos, as well as in 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 (morula) of human embryo development

• Initially, the totipotent cells in the embryo are unspecialised

• During development, totipotent cells begin to translate only part of their DNA, which results in cell specialisation

• These specialised cells then form tissues and are no longer classed as totipotent

• There are no totipotent cells present in the later stages of development as cells lose their ability to differentiate into any cell type