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Stem cells and totipotencyAQA A-Level Biology: Flashcards

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What can a totipotent cell do?

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What can a totipotent cell do?
Divide and produce any type of body cell.
When do totipotent cells occur in mammals?
Only for a limited time in early embryos.
Why do cells become specialised?
They translate only part of their DNA.
Where are pluripotent cells found?
In embryos.
Give two features of pluripotent cells.
They can divide in unlimited numbers and form many types of body cell.
Where are multipotent and unipotent cells found?
In mature mammals.
What is a multipotent cell?
A cell that divides to form a limited number of cell types, e.g. blood cells from bone marrow.
What is a unipotent cell? Give an example.
A cell that forms only one cell type, e.g. formation of cardiomyocytes.
What are iPS cells?
Pluripotent cells made from adult somatic cells using protein transcription factors.
Why are a patient's own iPS cells useful for treatment?
They are genetically identical, so not rejected and no immunosuppressants are needed.
Ethical objection to embryonic stem cells?
Obtaining them destroys embryos.
A risk of stem cell treatment?
Uncontrolled division, forming tumours.

Exam questions on Stem cells and totipotency

  1. A fertilised mammalian egg divides several times to form a ball of cells. If the cells are separated at the 4-cell stage, each one can develop into a complete embryo, including the placenta. If cells are taken from the same embryo a week later, they can form only some of the tissues of the body.
    Explain why a totipotent cell can form many different cell types, but a specialised cell in the same embryo cannot.2 marks
  2. Bone marrow in an adult contains stem cells that divide to produce red blood cells, several types of white blood cell and platelets. These cells never produce nerve cells or muscle cells. Bone marrow transplants are used to treat patients with leukaemia, whose own blood-forming cells have been destroyed by treatment.
    Explain why a transplant of bone marrow stem cells can replace the blood cells of a leukaemia patient but could not be used to replace damaged nerve cells.2 marks
  3. A patient has a heart muscle disorder. Researchers took skin cells from the patient, treated them with a set of protein transcription factors and obtained cells that behave like embryonic stem cells. They then induced these cells to form cardiomyocytes (heart muscle cells) to test drugs and possibly to transplant into the patient's heart.
    Describe how induced pluripotent stem (iPS) cells can be produced from the patient's cells.3 marks
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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).