8.2.1 Most of a cells DNA is not translated ( 8.0 The control of gene expression)

Question 1

what are stem cells

Answer 1

undifferentiated / unspecialised cells capable of :
1) dividing by mitosis to replace themselves indefinitely
2) differentiating into other types of cells

Question 2

describe how stem cells become specialised during development

Answer 2

• stimuli lead to activation of some genes due to transcription factors
• so mRNA is transcribed only from these genes and then translated to form proteins
• these proteins modify cells permanently and determine cell structure / function

Question 3

describe totipotent cells

Answer 3

• occur for a limited time in early mammalian embryos
• can divide and differentiate into any type of body cell

Question 4

describe pluripotent cells

Answer 4

• found in mammalian embryos
• can divide and differentiate into most cell types

Question 5

describe multipotent cells

Answer 5

• found in mature mammals
• can divide and differentiate into a limited number of cell types
  example : multipotent cells in bone marrow can divide and differentiate into different types of blood cell

Question 6

describe unipotent cells , using an example

Answer 6

• found in mature mammals
• can divide and differentiate into just one cell type
  example : unipotent cells in the heart can divide and differentiate into cardiomyocytes

Question 7

explain how stem cells can be used in the treatment of human disorders

Answer 7

• transplanted into patients to divide in unlimited numbers
• then differentiate into required healthy cells
  Examples :
• potential treatment of type 1 diabetes by creating healthy islets cells that produce insulin
• bone marrow stem cell transplant for sickle cell disease / blood cancers
  1) destroy patients bone marrow before treatment so no faulty cells are produced
  2) transplant stem cells from healthy person - divide and differentiate into healthy cells

Question 8

explain how induced pluripotent stem (iPS) cells are produced

Answer 8

1) obtain adult stomatic (body) cells from patient
2) add specific protein transcription factors associated with pluripotency to cells so they express genes associated with pluripotency
• transcription factors attach to promoter regions of DNA , stimulating or inhibiting transcription
3) culture cells to allow them to divide by mitosis
Once made , iPS cells can divide and differentiate into healthy cells to be transplanted into the same patient

Question 9

Evaluate the use of stem cells in treating human disorders

Answer 9

For :
- can divide and differentiate into required healthy cells , so could relieve human suffering by saving lives and improving quality of life
- embryos are often left over from IVF and so would otherwise be destroyed
- iPs cells unlikely to be rejected by patients immune system as made with patients own cells
- iPS cells can be made without destruction of embryo and adult can give permission
Against :
- ethical issues with embryonic stem cells as obtaining them requires destruction of an embryo and potential life
- immune system could reject cells and immunosuppressant drugs are required
- cells could divide out of control , leading to formation of tumours / cancers