Differentiation and Stem Cells Higher Human Biology Unit 1 – Sub-Topic 1 (a)

Learning Outcomes Differentiation: During embryological development the unspecialised cells of the early embryo differentiate into cells with specialised functions. Stem cells: Stem cells are relatively unspecialised cells that can continue to divide and can differentiate into specialised cells of one or more types. In the very early embryo, embryonic stem cells differentiate into all the cell types that make up the organism. Tissue (adult) stem cells replenish differentiated cells that need to be replaced and give rise to a more limited range of cell types. Tissue (adult) stem cells in the red bone marrow give rise to red blood cells, platelets and the various forms of phagocytes and lymphocytes. Once a cell becomes differentiated it only expresses the genes that produce the proteins characteristic for that type of cell.

Introduction The human body is made up of many specialised cells that perform specific functions. Specialised cells arise from the differentiation of unspecialised cells during embryological development. Differentiation also occurs in later developmental stages tissue repair etc in mature adults Link is to an animation on differentiation Differentiation is when an unspecialised cell becomes specialised in structure and biochemical properties, making them perfectly adapted for carrying out a particular function. http://www.educationscotland.gov.uk/highersciences/humanbiology/animations/stemcell.asp

Examples of Differentiation

Examples of Differentiation Ciliated epithelial cells line the trachea (windpipe) motor neurone cell They are perfectly suited to their job of sweeping dirty mucus up and away from the lungs. This is because those cells are only expressing the gene that codes for mucus. This means that the mucus gene is switched on and other genes, like the one that codes for insulin, are switched off. It has an axon (a long, insulated cytoplasmic extension). This structure is perfectly suited for transmitting nerve impluses. This is because those cells are only expressing the genes for neurotransmitters.

Stem cells…what do you know already? Use the questions below to help you complete a KWL chart to show the following information: K what you know already W what you want to learn about stem cells during this unit L complete this at the end of the unit to summarise what you have learned Some questions to think about… What is a cell? What varieties of cell exist? What is a tissue? Give some examples. What is an organ? Give some examples. What is a system? Give some examples. What is a stem cell? What are some different types of stem cells? What is the purpose of stem cell research? What are some ways that stem cells have been successfully used in medicine? What are some of the issues in stem cell research? What are some of the misconceptions that people have about stem cell research?

What are stem cells? Stem cells are unspecialised cells that have the ability to reproduce and differentiate into a diverse range of specialised cells. Why relatively? It is either unspecialised or not

Types of stem cells Embryonic Adult

Embryonic stem cells Embryonic stem cells are derived from an embryo about 4–5 days old (bastocyst). These early embryonic cells have the ability to differentiate into all of the cell types that make up an organism - pluripotent

Adult (tissue) stem cells Adult or tissue stem cells are found in small numbers in the tissues and organs of adults and children, including the brain, bone marrow, skeletal muscle and skin. These cells give rise to a much more limited range of cell types and will tend to develop into cell types that are closely related to the tissue in which they are found. They are multipotent. These cells replenish differentiated cells that need replaced in the tissues in which they are found.

Example of Adult Stem Cells

Other types of stem cells Stem cells can also be taken from the umbilical cord of new babies. Like adult stem cells, these cells can differentiate into a limited range of specialised cells.

Induced pluripotent stem cells Induced pluripotent stem cells are adult cells that have been genetically reprogrammed to an embryonic stem cell-like state. First video is method used by Gurdon and Yamanaka Second Video is an interview with Gurdon http://www.bbc.co.uk/news/science-environment-19878542 http://www.bbc.co.uk/news/science-environment-19872346

Questions Define the term differentiation. In what way is a ciliated epithelial cell a good example of a specialised cell? A goblet cell in the lining of the trachea produces mucus but not insulin. Explain briefly how this specialisation is brought about with reference to genes. Give two characteristics of stem cells. Name two types of stem cells found in humans. For each type of stem cell (Q5), identify one location where these cells can be found. Which type of stem cell is capable of differentiating into all the types of cell that make up the organism to which it belongs?

Answers Unspecialised cells of the early embryo become specialised in structure and biochemical properties, making them adapted for carrying out a particular function. They are a good example as they are perfectly suited to their job of sweeping dirty mucus up and away from the lungs. The cell is now only expressing the gene that codes for mucus/ only the mucus gene is switched on. The gene that codes for insulin is switched off. Two characteristics of stem cells are They reproduce themselves by repeated mitosis They can differentiate into specialised cells. Two types of stem cells in humans are Embryonic Adult Embryonic stem cells are found in embryo blastocysts, Adult stem cells are found in bone marrow, skin, skeletal muscle, brain.