cell differentiation and specialisation

• stem cells are undifferentiated cells that are capable of differentiating into specialised cells with a particular function
• cells differentiate as certain genes are switched off while others are expressed
• once animal cells have become specialised, they are fixed and can only produce copies of themselves via mitosis. however, plants cells can redifferentiate if needed.
• embryonic stem cells

  -embryos that are 3-5 days old

  -kills embryo

  -pluripotent- become any type of cell
• adult stem cells

  -come from some adult tissues such as bone marrow

  -can only develop into limited range of specialised cells- bone marrow can only differentiate into red or white blood cells

  -multipotent
• totipotent

  -stem cells which can form any type of cell in embryo plus cells of the placenta. most versatile
• pluripotent

  -can form any type of cells in embryo not placenta cells

  -less versatile than totipotent
• mulitpotent

  -adult stem cells which can only form limited number of cells

  -least versatile

  -bone marrow- red or white blood cells
• bone- marrow transplants

  -widely used for treatment of leukaemia, sickle- cell anaemia and immune disorders

  -makes use of multipotent adult stem cells

  -also used in cancer treatments- patients own bone marrow is removed and frozen then returned to body after chemotherapy
• drug research

  -drugs can be tested on adult stem cells rather than on animal tissues

  -gives a more valid result- animal cells may not always react in same way as animal cells would
• studying developmental biology

  -help scientists understand how organisms grow, develop and mature

  -observe how differentiation occurs and see what the consequences are if there is a developmental issue
• growing replacement cells, tissues, organs for transplant

  -type 1 diabetes- replacement pancreatic cells

  -grow nerve tissues for degenerative conditions such as alzheimers etc

  -grow replacement heart cells for patients who have suffered a heart attack
• problems with using stem cells

  -scientists don't know how to turn off and on all the genes

  -expensive, slow and difficult to control

  -ethical- exploiting one life to benefit another.
• differentiation- erythrocytes

  -lose nucleus, mitochondria, golgi apparatus, rough er

  -filled with haemoglobin

  -biconcave disc

  -squeeze through narrow capillaries and providing a large surface area for transporting oxygen
• differentiation- neutrophils

  -keep nucleus and filled with mitochondria

  -appear granular due to presence of lysosomes- phagocytosis
• cambium cells differentiate to xylem and phloem cells if needed