Unit 1: DNA and the Genome. Sub-Topic (1.4) Cellular Differentiation

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1 Unit 1: DNA and the Genome Sub-Topic (1.4) Cellular Differentiation Duncanrig 2016

2 Unit 1: DNA and the Genome Sub-Topic (1.4) Cellular Differentiation On completion of this subtopic I will be able to Cellular differentiation State that cellular differentiation is the process by which a cell develops more specialised functions by expressing genes characteristic for that type of cell. State that meristems are regions of unspecialised cells in plants that are capable of cell division. State that some of the cells in meristems differentiate into specialised cells and some remain meristematic. State that stem cells are unspecialised somatic cells in animals that can divide to make copies of themselves (self renew) and /or differentiate into specialised cells. State that stem cells in the very early embryo can differentiate into all cell types that make up and organism. They are pluripotent. State that tissue (adult) stem cells are needed for growth and repair. Tissue stem cells replenish differentiated cells that need to be replaced and give rise to a more limited range of cell types found only in the tissue it has come from. They are multipotent. Explain that once differentiated a cell will only express the genes that produce the proteins characteristic for that type of cell. State that embryonic stem cells can self renew in the lab (in vivo) and are used as a source of stem cells in research. State that therapeutic use of stem cells enables the repair of damaged or diseased organs. e.g. used in skin grafts, bone marrow transplants and cornea repair. Stem cell research provides information on how cell processes such as differentiation and gene regulation work. Stem cells can be used as model cells to study how diseases develop or for drug testing. Discuss the ethical issues of stem cell use and the regulation of their use. Page 2 of 11

3 Prior Learning Unit (2.2) Stem cells and meristems Stem cells in animals can divide continuously and have the potential to become different types of cell Specialisation/ differentiation is the process by which an unspecialised cell becomes altered and adapted to perform a special function as part of a permanent tissue All organisms exhibit growth Stem cells are involved in growth and repair Meristems are the sites of production of non-specialised cells in plants Meristems are the sites of cell division (mitosis) in a plant There are apical and lateral meristems Cells produced at the meristems have the potential to become different types of cell Cells produced at the meristems contribute to plant growth Discuss the potential uses and ethical issues associated with stem cell research Page 3 of 11

4 Cellular differentiation A multicellular organism consists of a large number of cells. Rather than all cells carrying out every function for the maintenance of life a division of labour occurs and most of the cells become specialised (differentiated) and carry out their own particular function. Differentiation is the process by which a cell develops more specialised functions by expressing genes characteristic for that type of cell. This means that during development, as a cell becomes specialised some genes are switched on and some are switched off. Genes for vital metabolites (e.g. genes involved in the production of enzymes for respiration) are switched on (expressed) in all cells. Whereas genes not required for proteins characteristic of a cell are switched off. State the meaning of the term differentiation. Using Torrance page 44 describe what happens during differentiation to allow the cell to become specialised During differentiation: Page 4 of 11

5 Growth and Differentiation in Multicellular Plants In plants growth is restricted to specific regions called meristems. These are the only places where growth can occur. They are regions of unspecialised cells which undergo mitosis to produce cells that either remain meristematic or differentiate into specialised cells as they move further away from the meristem. Apical meristems are located in of the plant. They increase the height of the plant. Lateral meristems are found in the cambium layer between the xylem and phloem tissue. They increase the of the plant. Page 5 of 11

6 Growth and Differentiation in Multicellular Animals Unlike plants animal tissues can grow in all areas. A multicellular animal (e.g. human) begins life as a fertilised egg (zygote). Like the cells in an adult, each embryonic cell possesses all the genes required for making a whole organism. At this early stage the cells are unspecialised. As development proceeds, the cells undergo differentiation and become specialised in structure, making them perfectly adapted for carrying out a particular function. Stem Cells Stem cells are unspecialised somatic cells that can divide to make copies of themselves (self renew) and /or differentiate into specialised cells. Tissue Stem Cells Tissue (adult) stem cells are found in all parts of the body. They are needed for growth and repair. They are unspecialised cells that can divide to make copies of themselves. This process is called self-renewal. Alternatively they can differentiate into a limited number of cell types which are characteristic of their location in an organism. Stem cells are the organism s internal repair system and can divide without limit to replace other cells such as a muscle cell, a red blood cell or a brain cells. They are multipotent. Once differentiated, a cell will only express the genes that produce the proteins characteristic for that type of cell. Page 6 of 11

7 Embryonic Stem Cells Embryonic stem cells are present in embryos within the womb. These cells form at the blastocyst stage of development. A blastocyst is a hollow ball of cells that is smaller than a pinhead. The embryonic stem cells lie within this ball of cells. Embryonic stem cells do not form new stem cells (self-renew), however, they are capable of dividing to form any types of specialised cell that make up and organism. They are pluripotent. 1. Name the two types of stem cell found in humans. 2. For each type of cell identify one location where these cells can be found. 3. Describe the different properties of the two types of stem cell. 4. After a stem cell differentiates only certain genes are expressed. Explain how this results in different cell types. Page 7 of 11

8 Research Value of Stem Cells 1. The key aim is to promote the therapeutic use of stem cells to replace damaged or diseased organs. 2. Stem cell research provides information on how cell processes such as cell growth, differentiation and gene regulation work. 3. Stem cells can be used as model cells to study how diseases develop. 4. Drug testing. Sources of Stem Cells 1. Embryonic stem cells can self renew in the lab (in vivo). They are used as a source of stem cells in research. Stage A After fertilisation, the zygote undergoes rapid cell division) and produces a multicellular ball. Stage B The cells reorganise and form a hollow ball containing fluid in the cavity. This implants in the uterus. Stage C The implanted ball of cells now begins to differentiate. Embryonic stem cells are derived from embryos at stage B, before implantation occurs. 2. Adult stem cells can be cultured to produce multipotent stem cells which can replace damaged or diseased tissue or for research. 3. Induced Pluripotent Stem cells (IPS) In this technique adult cells are reprogrammed to become undifferentiated, self-renewing pluripotent stem cells. Page 8 of 11

9 Therapeutic Value of Stem Cells As well as having the ability to undergo cell division, embryonic stem cells are able to undergo cell differentiation to replace damaged or diseased organs and tissues. Using Torrance p49-51 describe some current therapeutic uses of stem cells: Using Torrance p49-51 describe possible future therapeutic uses of stem cells: Page 9 of 11

10 Ethical Issues Ethics refers to the moral values and rules that ought to govern human conduct. The use of stem cells raises several ethical issues. Certain control measures have been put in place to try to prevent any illegal or unethical uses of stem cells and ensure that the quality of stem cells and procedures is of a high standard. Consider the ethical issues this raises; include arguments for and against the use of human embryonic stem cells under the following headings: Moral Health Safety Page 10 of 11

11 Sub-topic 1.4 Cellular Differentiation How well do you rate your knowledge and understanding? Complete: Column 1 before your Unit assessment Column 2 before your Prelim Column 3 before your May exam I can State that cellular differentiation is the process by which a cell develops more specialised functions by expressing genes characteristic for that type of cell. State that meristems are regions of unspecialised cells in plants that are capable of cell division. State that some of the cells in meristems differentiate into specialised cells and some remain meristematic. State that stem cells are unspecialised somatic cells in animals that can divide to make copies of themselves (self renew) and /or differentiate into specialised cells. State that stem cells in the very early embryo can differentiate into all cell types that make up and organism. They are pluripotent. State that tissue (adult) stem cells are needed for growth and repair. Tissue stem cells replenish differentiated cells that need to be replaced and give rise to a more limited range of cell types found only in the tissue it has come from. They are multipotent. Explain that once differentiated a cell will only express the genes that produce the proteins characteristic for that type of cell. State that embryonic stem cells can self renew in the lab (in vivo) are used as a source of stem cells in research. State that therapeutic use of stem cells enables the repair of damaged or diseased organs. e.g. used in skin grafts, bone marrow transplants and cornea repair. Stem cell research provided information on how cell processes such as differentiation and gene regulation work. Stem cells can be used as model cells to study how diseases develop or for drug testing. Discuss the ethical issues of stem cell use and the regulation of their use. Page 11 of 11