ka4: cellular differentiation

• Cellular differentiation is the process by which a cell expresses certain genes to produce proteins characteristic for that type of cell. This allows a cell to carry out specialised functions.
• Differentiation into specialised cells from meristems in plants; embryonic and tissue (adult) stem cells in animals.
• Meristems are regions of unspecialised cells in plants that can divide (self-renew) and/or differentiate.
• Stem cells are unspecialised cells in animals that can divide (self-renew) and/or differentiate.
• There is no requirement to learn examples of differentiated animal and plant cells.
• Cells in the very early embryo can differentiate into all the cell types that make up the organism and so are pluripotent.

  • All the genes in embryonic stem cells can be switched on so these cells can differentiate into any type of cel
• Tissue stem cells are involved in the growth, repair and renewal of the cells found in that tissue. They are multipotent.

  • Tissue stem cells are multipotent as they can differentiate into all of the types of cell found in a particular tissue type. For example, blood stem cells located in bone marrow can give rise to all types of blood cell.
• Therapeutic and research uses of stem cells.

  • The therapeutic uses of stem cells should be exemplified by how they are used in corneal repair and the regeneration of damaged skin.
• Therapeutic uses involve the repair of damaged or diseased organs or tissues.

  • Stem cells from the embryo can self-renew, under the right conditions, in the lab.
• Research uses involve stem cells being used as model cells to study how diseases develop or being used for drug testing.

  • Stem cell research provides information on how cell processes such as cell growth, differentiation and gene regulation work.
• The ethical issues of using embryonic stem cells.

  • Use of embryonic stem cells can offer effective treatments for disease and injury; however, it involves destruction of embryos.
• Cellular differentiation is the process by which a cell expresses certain genes to produce proteins characteristic for that cell type. This allows a cell to carry out specialised functions.
• Every cell contains all the genes for constructing the whole organism.  These genes all have the potential to be switched on or off
• During differentiation:

  • many genes remain switched on
  • cell specific genes (control features specific to this type of differentiated cell) are switched on
  • unnecessary genes (control features not specific to this type of cell) are switched off.
• Once a cell becomes differentiated it only expresses the genes that code for the proteins specific to that particular type of cell.
• For example, a red blood cell.

  
• Meristems are regions of unspecialised cells in plants that are capable of cell division (self-renewing) throughout the life of the plant.

  Some of the cells remain as part of the meristem while others become differentiated.

   

  There are two types of meristem in plants:

  1. Apical:

  • Found at the root and shoot tips.
  • Cause an increase in the height of the plant and length of the roots.

   

  1. Lateral:

  • Found in the stem of the plant.
  • Made up of cambium cells.
  • Cause an increase in the girth of the plant

  
• Stem cells are unspecialised cells in animals that can:

  • divide to make copies of themselves (self-renew) while remaining unspecialised
  • differentiate into specialised cells.

  
• An early human embryo (blastocyst) consists entirely of embryonic stem cells.  All of the genes in an embryonic stem cell have the potential to be switched on, therefore the cell is pluripotent. This means it is capable of differentiating into all of the cell types in the human body
• These cells do not self-renew in vivo (within the living organism), but can under the right conditions in the lab. It is then they are termed embryonic stem cells and are used as a source of stem cells in research
• Tissue (adult) stem cells are needed for growth, repair and renewal of tissues. They have a much narrower differentiation potential than embryonic stem cells because many of their genes are already switched on.
• Tissue stem cells replenish differentiated cells that need to be replaced and are multi-potent.  This means they give rise to a more limited range of cell types, e.g. blood stem cells found in the bone marrow produces the various blood cell types.

  
• Once a cell becomes differentiated it only expresses the genes that produce the proteins characteristic for that type of cell.
• Stem cell research provides information on cell processes such as cell growth and differentiation.  It is hoped that this will lead in turn to a better understanding of gene regulation including the molecular biology of cancer.
• Stem cells can also be used as model cells to study how diseases develop or for drug testing.
• Human stem cells can be grown in optimal culture conditions provided that certain growth factors are present.  As they can be readily grown in the laboratory they are now being used therapeutically (to treat disease).
• • Corneal transplants

  Damage to the cornea of the eye by chemical burning can be treated using stem cells. Stem cells located at the edge of the patient’s cornea are grown in the lab and then grafted onto the surface of the damaged eye. In most cases the person’s eyesight is restored
• • Skin grafts

  Human embryonic stem cells are grown on a synthetic (man-made) scaffold to produce layers of skin cells. This stem cell tissue acts to repair damaged skin
• Ethics – the moral values and rules that govern human conduct.

  The use of stem cells raises an ethical issue:

  • Destruction of human embryos to create embryonic stem cell lines. This is considered by some to be unethical practice