As Biology Unit 2 - Stem Cells

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Stem Cell Deffinations

  • What are Stem Cells?:
    • They are undifferentiated cells
    • They can give rise to other types of cell
    • There is no limit on the number of divisions it can do
    • There are different types of stem cell: Pluripotent and Totipotent.
  • Pluripotent Stem Cells can:
    • Give rise to many different cell types
    • Cannot give rise to embryonic cells
    • Some of the genes have been deactivated.
  • Totipotent Stem Cells can:
    • Give rise to all 216 cell tyoes
    • They are undifferentiated and unspecalised
    • They can keep dividing
    • All the genes have the potential to be active as no genes have been switched off.
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  • How to stem cells become differentiated cells?
    • A chemical stimulus is given to the unspecalised cells
    • This causes some genes to be switched on and become active and genes to be switched off.
    • mRNA is only made from active genes
    • The mRNA moves to the ribosomes.
    • The ribosomes read teh mRNA adn make the appropiate protein.
    • The protein can pernanently alter the structure and function of the cells.
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Sources of Stem Cells

  • Embryonic Stem Cells:
    • Advantages --> Easy to extract and grow
    • Disadvantages --> Ethical issues, possible rejection by patients body, risk of infection when cells recived, risk of stem cells becoming cancerous in body.
  • Adult Stem Cells:
    • Advantages --> Fewer ethical issues, rejection risk is avoided if stem cells are taken from the patient.
    • Disadvantages --> Difficult to extract, more difficult to produce different cell types, risk of infection when cells are extracted or recieved.
  • Fused Cells:
    • A nucleus taken from the patients body cell is inserted into a human cell with the nucleus removed. It divides to produce stem cells with the patients DNA.
    • Advantages -->Rejction risk avoided if nucleus is taken from the patient, there is a potential for treating genetic disorders.
    • Disadvantages --> Ethical issues with the source of embryonic nuclei, risk of infection when cells recieved, risk of stem cells becoming cancerous in body. 
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Risks with recieving stem cells

  • Possible route to infection
  • Rejected by patient
  • Increased chance of the patient becoming cancerous
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