stem cells

why does cell differentiation occur?

differential gene expression

what is a stem cell?

• unspecialised/undifferentiated cell that retains the ability to divide

• so can differentiate into specialised cells

describe stem cell division:

• one cell starts the process of differentiation

• one cell still undifferentiated - self renewal

what are the 4 types of stem cell?

• totipotent

• pluripotent

• multipotent

• unipotent

what is a totipotent stem cell? give an example:

• stem cells which can differentiate into any cell of the body i.e. all genes can be expressed

• this means they can form entire organisms

• e.g. zygote - cells in early mammalian embryos

how do totipotent cells become specialised?

translate only part of their DNA during development

what is a pluripotent stem cell? give an example:

• can differentiate into most cells of the body but cannot form whole organisms (as they cannot form placenta/umbilical cord - genes coding for these are not expressed)

• e.g. embryonic cells become pluripotent from totipotent after first few divisions

what is a multipotent stem cell?

• can differentiate into a limited no. of cell types

• e.g. adult stem cells found in the bone marrow

what is a unipotent stem cell?

• can only differentiate into one type of cell

• e.g. stem cells which differentiate into cardiomyocytes

what are cardiomyocytes? how can they be regenerated?

• muscle cells which comprise heart tissue

• unipotent stem cells that can only differentiate into cardiomyocytes allow cardiomyocytes to be regenerated
  (as cardiomyocytes are unable to /)

state how induced pluripotent stem cells (iPS cells) can be produced:

can be produced from adult somatic cells using appropriate protein transcription factors

describe the process of making iPS cells:

• healthy differentiated cells (e.g. skin cells) extracted from patient

• differentiated cells undergo mitosis

• add virus w/ genes coding for transcription factors associated w/ pluripotent stem cells

• makes the differentiated cells dedifferentiate into iPS as genes transferred into adult cell’s DNA so cell is able to produce transcription factors

• add growth factor to differentiate into cells of interest (e.g. heart cells)

• inject iPS into patient

describe the stages of using pluripotent stem cells in gene therapy:

• obtain pluripotent embryonic stem cells - undergo mitosis

• add hormone/growth factors to encourage cell differentiation

• each group grows into a colony

• differentiation factors added to colonies in separate containers to aid specialisation

• inject pluripotent stem cells into patient

give 2 diseases that stem cell therapy could treat:

• type 1 diabetes

• sickle cell anaemia

give the advantages of using stem cells to treat human disorders:

• use of iPS cells prevents possibility of immune rejection and does not require embryo destruction

• save lives e.g. can be used to grow organs for those awaiting transplants

• can improve quality of life

give the disadvantages of using stem cells to treat human disorders:

• using embryonic stem cells results in the destruction of embryos

• use of adult stem cells less useful - only multipotent/unipotent