Specification points Specification points Starter Objectives Grade Objectives 4/5 To be able to define a stem cell 6/7 To be able to describe the function of stem cells in embryos, adult animals and plants and in treating medical conditions 8/9 To be able to evaluate the potential risks, benefits, social and ethical issues surrounding the use of stem cells in medical research and treatment Set your own objective – what would you like to have achieved by the end of this topic? Here’s some help… Keywords Specialised Embryos Differentiate Cloning Medical uses Repair Multicellular Bone Marrow Stem Cells During the development of an embryo, most of the cells become specialised. They cannot later change to become a different type of cell. But embryos contain a special type of cell called stem cells. These can grow into any type of cell found in the body. They are unspecialised cells. Stem cells • Stem cells are cells found in most, if not all, multi- cellular animals • They are characterized by the ability to renew themselves through mitotic cell division and can change into a wide range of specialized cell types. They are found throughout the organism • All cells in a particular organism have the same number of chromosomes with the same types of genes e.g. all human cells have 46 chromosomes with the same information on all of their genes How then can different types of cells be produced? • A stem cell has all the genetic information available for a particular organism. To become one particular, specialised cell a stem cell can switch off certain genes so that those genes do not affect how the cell develops. • If a stem cell is producing a different type of specialised cell then different genes will be switched off and other will remain active. • By this method multicellular organisms can make many different types of cells to carry out different types of functions .e.g. if a stem cell were to be changed into a red blood cell it would have the gene switched on that produces the protein haemoglobin, the oxygen carrying substance. If making a hair cell this gene would obviously not need to be switched on What is a stem cell? stem cell SELF-RENEWAL (copying) DIFFERENTIATION (specializing) stem cell specialized cell e.g. muscle cell, nerve cell stem cell Stem cells are different from other cells of the body because stem cells can both: 1)Self-renew: Make copies of themselves • AND • 2) Differentiate: Make other types of cells – specialized cells of the body. SELF-RENEWAL (copying) DIFFERENTIATION (specializing) stem cell specialized cell e.g. muscle cell, nerve cell What is a stem cell? Stem cell SELF-RENEWAL (copying) Identical stem cells Stem cell DIFFERENTIATION (specializing) Specialized cells Why self-renew AND differentiate? 1 stem cell 4 specialized cells 1 stem cell Self renewal - maintains the stem cell pool Differentiation - replaces dead or damaged cells throughout your life Why self- renewal and differentiate? • 1) Self renewal is needed because if the stem cells didn’t copy themselves, you would quickly run out. It is important for the body to maintain a pool of stem cells to use throughout your life. • 2) Differentiation is important because specialized cells are used up, damaged or die all the time during your life. Specialized cells cannot divide and make copies of themselves, but they need to be replaced for your body to carry on working. For example, your body needs 100,000 million new blood cells every day. Of course, differentiation is also important for making all the different kinds of cell in the body during development of an embryo from a single fertilized egg. Where are stem cells found? embryonic stem cells blastocyst - a very early embryo tissue stem cells fetus, baby and throughout life Stem cell jargon Potency A measure of how many types of specialized cell a stem cell can make Pluripotent Can make all types of specialized cells in the body Embryonic stem cells are pluripotent Multipotent Can make multiple types of specialized cells, but not all types Tissue stem cells are multipotent Fill in the gaps • A stem cell is an _____ cell of an organism that is capable of giving rise to ____ more cells of the same type called ___-____, and from which certain other cells can arise from a process called _______ • Word bank: self-renewal, many, differentiation, undifferentiated • An embryo develops from a fertilised egg. Cells at the early stages in the development of the embryo are stem cells. • If cells are removed from the embryo – called embryonic stem cells - they will differentiate into any cell type. • Some stem cells remain in the bodies of adults – adult stem cells. Adult stem cells are found in limited numbers at certain locations in the body. • Adult stem cells can be found in several regions of the body, including the: • • • • • • • • brain eyes blood heart liver bone marrow skin muscle • Adult stem cells can differentiate into related cell types only, for example, bone marrow cells can differentiate into blood cells and cells of the immune system but not other cell types. Embryonic stem cells • These come from the inner cell mass of the blastocyst • Embryonic stem cells can differentiate into any kind of cell • They are pluripotent • But why use them? Embryonic stem (ES) cells: Where we find them blastocyst cells inside = ‘inner cell mass’ outer layer of cells = ‘trophectoderm’ embryonic stem cells taken from the inner cell mass fluid with nutrients culture in the lab to grow more cells Embryonic stem (ES) cells: What they can do differentiation embryonic stem cells PLURIPOTENT all possible types of specialized cells Adult Stem Cells We have stem cells in our body • eg. In bone marrow, there are three types of stem cell, one for blood, one for bone, and one for skin. This is called multipotency – and means there is a limit to what the stem cells can become • An advantage to using adult cells could be that tissues created from them won’t be rejected Tissue stem cells: Where we find them surface of the eye skin testicles brain breast intestines (gut) bone marrow muscles Tissue stem cells: What they can do blood stem cell differentiation found in bone marrow MULTIPOTENT only specialized types of blood cell: red blood cells, white blood cells, platelets • Tissue stem cells can often make several kinds of specialized cell, but they are more limited than embryonic stem cells. Tissue stem cells can ONLY make the kinds of cell found in the tissue they belong to. So, blood stem cells can only make the different kinds of cell found in the blood. Brain stem cells can only make different types of brain cell. Muscle stem cells can only make muscle cells. And so forth. • Scientists say that tissue stem cells are multipotent because they can make multiple types of specialized cell, but NOT all the kinds of cell in your body. Quick questions • Why do stem cells need to self renew AND differentiate? • Which type of stem cell is most useful? • Where are adult stem cells found? • What is meant by the term multipotency? Using stem cells • Stem cells can divide to produce new cells, which can then divide into different cell types. They therefore have the potential to be transplanted into patients to treat medical conditions and disease. They could be used to replace cells that have been damaged or destroyed, eg: • in type 1 diabetes • in cases of multiple sclerosis, which can lead to paralysis • in cases of spinal cord or brain injury, that have led to paralysis • The stem cells used could be: • embryonic stem cells • adult stem cells • Embryonic stem cells can differentiate into a wider range of cell types, but are difficult to obtain and their use raises ethical challenges. The best source is the five-day-old embryo. • Adult stem cells will differentiate into a narrower range of cell types. Bone marrow transplants are an example of adult stem cell transplant. Bone marrow cells will differentiate into different types of blood cell. Bone marrow transplants are carried out: • in cases of blood cell cancer such as leukaemia and lymphoma • when blood cells have been destroyed by cancer treatment Induced pluripotent stem cells (iPS cells) ‘genetic reprogramming’ = add certain genes to the cell adult cell induced pluripotent stem (iPS) cell behaves like an embryonic stem cell differentiation culture iPS cells in the lab Advantage: no need for embryos! all possible types of specialized cells What are iPS cells? • In 2006, scientists discovered that it is possible to make a new kind of stem cell in the laboratory. They found that they could transform adult skin cells from a mouse into cells that behave just like embryonic stem cells. In 2007, researchers did this with human cells too. The new stem cells that are made in the lab are called induced pluripotent stem cells. Just like embryonic stem cells, they can make all the different types of cell in the body – so we say they are pluripotent. • Making induced pluripotent stem (iPS) cells is a bit like turning back time. Scientists add particular genes to adult cells to make them behave like embryonic stem cells. Genes give cells instructions about how to behave. So, this process is a bit like changing the instructions in a computer programme to make the computer do a new task. Scientists call the process they use to make iPS cells ‘genetic reprogramming Quick questions • Name 2 ways in which stem cells can be used for medical reasons? • What does iPS stand for? • What are the benefits of iPS cells? The Hayflick Limit • Think on this: Can cells replicate forever? • Differentiated cells have a limit to the number of times they can divide telomeres • This is what eventually causes old age • The only two exceptions are … Stem cells and cancer cells Task: Answer the following questions in your book: 1. What are some of the uses of stem cells? 2. What’s a difference between adult stem cells and embryonic stem cells? 3. How are stem cells currently being used to treat medical conditions? 4. Describe how therapeutic cloning can be used and the social and ethical concerns with this procedure 5. What are Meristems? Self-assessment: 1. Repair damaged organs, bones and cartilage and help to treat certain medical conditions. 2. An embryonic stem cell has the ability to differentiate into a wide variety of cell types whereas an adult stem cell can only differentiate into a few cell types. 3. In 2016 stem cells have been used in multiple sclerosis sufferers in order for them to regain mobility. The most widely used stem cell treatments are for people with conditions of the blood. Accept any acceptable use for stem cells 4. Therapeutic cloning involves growing an embryo using cloned cells from a human, the embryonic stem cells are removed and used to grow organs/tissues which can then be replaced in that human. Concerns regarding when life begins and whether we are playing ‘God’. 5. Meristems are areas of the plant where unspecialised cells group together, this is where the majority of growth takes place. Meristems • Cells from meristems can be cloned. Meristematic cells are removed from a plant and grown in tissue culture. The cells are grown in a culture medium that contains agar – to provide support and water for the growing cells – along with nutrients and plant hormones to stimulate growth and cell division. • Plants are cloned to produce identical plants quickly and economically. • Producing new plants by cloning is quicker than allowing plants to reproduce and collecting and sowing seeds. It’s therefore an effective way of producing new individuals from rare and endangered plants, helping to preserve the species. • Clones will be genetically identical to the original plant providing the meristem cells. This is useful to provide crop plants for large-scale cultivation that have desirable characteristics such as disease resistance. • Tissue culture and cloning are important in growing identical plants produced by genetic engineering. • Cloning in plants also occurs naturally, for instance, in runners in strawberry plants. An older, simpler method of cloning plants that gardeners use to produce new, identical plants is by taking cuttings. Meristem are areas of plant tissue at which growth occurs. Cells in these tissue have the ability to divide and specialise to become one of a number of different types of cell. The cells in the Meristem have the ability to divide over and over again to produce non-specialised cells. Some of these cells continue to divide, allowing the plant to grow taller and wider throughout its life. 1. What’s the name of plant stem cell tissue? 2. How is it similar to adult stem cells and how is it different? Extra Challenge: Why are scientists especially interested in studying plant stem cells? Evaluation: Benefits and risks (Grade 8/9) • Stem cells have great potential, in treating patients with currently untreatable conditions, growing organs for transplants, and research. But there are clinical, ethical and social issues with their use. These issues will be different for growth and transplant of adult, embryonic and therapeutically-cloned stem cells. They will also depend on whether the stem cells are to be used for therapy or research. • It is important to obtain a balanced view. Sometimes, there are no right or wrong answers, or even answers at all. Clinical issues • There is no guarantee how successful these therapies will be, for example the use of stem cells in replacing nerve cells lost in Parkinson’s disease patients. • The current difficulty in finding suitable stem cell donors. • The difficulty in obtaining and storing a patient’s embryonic stem cells. These would have to be collected before birth - some clinics offer to store blood from the umbilical cord when a person is born. • Mutations have been observed in stem cells cultured for a number of generations, and some mutated stem cells have been observed to behave like cancer cells. • Cultured stem cells could be contaminated with viruses which would be transferred to a patient. Ethical issues • A source of embryonic stem cells is unused embryos produced by in vitro fertilisation (IVF) • For therapeutic cloning is it right to create embryos for therapy, and destroy them in the process? • Embryos could come to be viewed as a commodity, and not as an embryo that could develop into a person. • At what stage of its development should an embryo be regarded as, and treated as a person? Social issues • Educating the public about what stem cells can, and can't do, is important. • Whether the benefits of stem cell use outweigh the objections. • Much of the research is being carried out by commercial clinics, so reported successes are not subject to peer review. Patients could be exploited by paying for expensive treatments and being given false hope of a cure as stem cell therapies are only in their developmental stages. Ethical Issues • Discussion: Are embryonic stem cells better to use than adult stem cells? • Using embryonic stem cells destroys the embryo. • Is it right to exchange one life for another? • Do the benefits outweigh the costs? • Will it lead to designer babies? A life for a life?? Task: Using the opinion cards: 1. In pairs, discuss some of the pros and cons of the use of stem cells in medical research and treatment 2. Sort the cards into two columns – fact and opinion Scientists around the world are working on techniques to refine stem cell therapy. "If someone is going to have an abortion, isn’t it better that we use it for something useful?" Embryonic stem cells kill innocent embryos. This is murder. When a stem cell divides, each new cell has the potential to either remain a stem cell or become another type of cell with a more specialised function. Stem cells are pluripotent which means they have the ability to become any type of cell. Adult cells have lost this ability. Stem cells may also provide a useful way to test the effects of experimental drugs. I don’t mind people researching with adult stem cells. But I do not think embryonic stem cells should be used because that is ending the life of a baby. No-one dies if you use adult stem cells. Stem cell therapy could treat Parkinson's disease, Alzheimer's disease, heart disease, stroke, arthritis, diabetes, burns and spinal cord damage. Fact Scientists around the world are working on techniques to refine stem cell therapy. Stem cells may also provide a useful way to test the effects of experimental drugs. Stem cells are pluripotent which means they have the ability to become any type of cell. Adult cells have lost this ability. When a stem cell divides, each new cell has the potential to either remain a stem cell or become another type of cell with a more specialised function. Opinion I don’t mind people researching with adult stem cells. But I do not think embryonic stem cells should be used because that is ending the life of a baby. No-one dies if you use adult stem cells. "If someone is going to have an abortion, isn’t it better that we use it for something useful?" Embryonic stem cells kill innocent embryos. This is murder. Stem cell therapy could treat Parkinson's disease, Alzheimer's disease, heart disease, stroke, arthritis, diabetes, burns and spinal cord damage. Therapeutic cloning • Adult stem cell transplants use a patient's own stem cells. They are therefore genetically identical and will not be rejected by the patient's immune system. • There are also fewer complications if the stem cells come from a close member of the family. Alternatively, donor cells can come from a person with closely-matched tissue types. • Remember: Embryonic stem cells will always come from a donor – unless stem cells were collected from the patient as an embryo. • Therapeutic cloning could produce stem cells with the same genetic make-up as the patient. • The technique involves the transfer of the nucleus from a cell of the patient, to an egg cell whose nucleus has been removed. • Stem cells produced in this way could be transferred to the patient. Although human stem cells have been produced in this way, and used in research, there is no evidence that, as yet, they have been used to treat anyone. • What was your mark out of 25? • Compare adult stem cells with embryonic stem cells (3 marks) • What are meristems? (2 marks) • In what ways can stem cells be used in the medical industry? (3 marks) • What is therapeutic cloning? Name one benefit of therapeutic cloning (3 marks) • Evaluate the use of stem cells for therapy. Refer to clinical, social and ethical reasons in your answer. (6 marks) • Name 1 way in which farmers can use meristems for commercial reasons. (1 mark) Refer back to your objective • Were you able to meet this objective? • What went well in this lesson? • What could have been better? • What further questions do you have regarding this topic?
