In this essay I will explain the generation of specialised tissue from embryonic stem cells and compare and contrast cancer cells and normal cells.
Embryonic stem cells start out as essentially blank cells, we call these totipotent cells they have the opportunity to become any type of cell in the body. As a ball of cells becomes an embryo these stem cells slowly change and differentiate to create specialised tissue. The process starts at when the nuclei of the haploids (male and female gametes) fuse to become the Zygote. This then becomes the morula as the cells divide and multiply, this all happens 2-4 days after fertilisation. It’s when it becomes the blastocyst that the stem cells start differentiating forming the trophoblast which becomes the placenta and the pluriblast becoming the inner cell mass (Jordan, R. 2018). Once the stem cells have chosen a path, they can no longer go back to totipotency, at this stage the pluriblast is made up of pluripotent stem cells meaning they can become any cell except the placenta. As the cells continue to divide and multiply 3 distinct layers are formed, these are known as germinative tissues or germ layers. The three germ layers go on to form different tissues in the developing ball of cells once it implants and starts to grow, the ectoderm becomes the neutral tissues such as skin cells, brain cells and hair cells. The mesoderm becomes the muscles, bones and connective tissue along with tissue to form the circulatory and urinary system and the reproductive organs. Lastly the endoderm becomes the tissues that forms the digestive and respiratory systems, the process of these distinct layers forming is called gastrulation (Gilbert and Raunio, 1997 page 468). For better understanding you can refer to Fig.1, after this is becomes difficult to see what is going on as the cells implant into the uterine wall to start forming the placenta and provide nutrients needed for growth and development of the embryo into a baby. The changes in the stem cells that cause them to differentiate are triggered by different genes activating or switching off at a specific time. An example of one type of gene is the Hox genes, humans have 4 sets of these genes they determine which end of the tube of cells will become the head and which will become the bottom part of the body by being active in different places at different time through development (Shubin 2009 page 109). The research into embryonic stem cells and what they are capable of is ongoing even though we have learnt a lot in the last 20 years there is still a lot we don’t know about them.
Figure 1 diagram showing the 3 germ layers, drew from Your Inner Fish by Neil Shubin (2009) page 103.
Once differentiation has occurred embryonic stem cells are just normal cells a few adult stem cells stick around in areas of the body to help with repair when needed. They are found in many places including bone marrow, blood and adipose tissue. Normal cells make exact copies when required as old or damaged cells die off, they stay in the area of the body they are supposed to for example kidney cells stay in the kidneys, liver cells stay in the liver. Healthy cells also know when to stop producing copies as not to have too many cells in one area, that is one of the main differences between normal cells and cancer cells. The mutation that occurs in cancer cells causes them to produce new cells almost constantly they ignore or turn off the gene that tells cells there is enough of them, they also do not die when damaged or old, this is what causes tumours. In normal cells they receive chemical signals that keep them in the right part of the body, cancer cells ignore these signals allowing them to spread to different parts of the body from where they originated. Another quality of cancer cells that allow this to happen is that they do not secrete substances to stick together like normal cells do so it’s easier for them to separate from the group (Eldridge, 2018). Angiogenesis is another time normal cells and cancer cells behave in different way, normal cells with only attract blood when needed for growth and repair where as a cancer cell will unnecessarily (Pecorino, n.d.). Cancer cells are also very unstable, they have abnormal numbers of chromosomes that get more unstable and abnormal with each new cell produced as they do not make exact copies like normal cells. According to Lynne Eldridge in 2018 the 2 types of cell also look very different under a microscope with cancer cells lacking a consistent shape not just with the body of the cell but also the nucleus. This is not the case with normal cells, as they make exact copies of themselves there is consistence with shape and size of the same type of cell. As discussed earlier normal cells differentiate, cancer cells do not do this, they never mature just mutate DNA and divide. They also do not need oxygen to produce energy like normal cells, instead they use glucose apparently 5 to 10 times more than a normal cell (The Truth About Cancer, 2018). There is a struggle to find similarities between normal cells and cancer cells as they are so different but, cancer cells are just the mutated version of a normal cell.
In conclusion in this essay I have explained the generation of specialised tissue from embryonic stem cells and compared and contrasted normal cells and cancer cells.
Closerlookatstemcells.org. (2018). Types of Stem Cells. online Available at: http://www.closerlookatstemcells.org/learn-about-stem-cells/types-of-stem-cells Accessed 2 Oct. 2018.
Nature.com. (2018). Cell Differentiation, Tissue | Learn Science at Scitable. online Available at: https://www.nature.com/scitable/topicpage/cell-differentiation-and-tissue-14046412 Accessed 2 Oct. 2018.
Gilbert, S. and Raunio, A. (1997). Embryology. Sunderland, MA: Sinauer Associates.
Pecorino, L. (n.d.). Molecular biology of cancer. 4th ed.ce
Jordan, R. (2018) Lecture: Stem Cells, PowerPoint, Biology: Cell Biology, South and City College Birmingham, delivered 24th September 2018.
Shubin, N. (2009). Your inner fish. London: Pengiun Books.
Eldridge, MD, L. (2018). Cancer Cells vs. Normal Cells: How Are They Different?. online Verywell Health. Available at: https://www.verywellhealth.com/cancer-cells-vs-normal-cells-2248794 Accessed 9 Oct. 2018.
The Truth About Cancer. (2018). 5 Unique Characteristics of Cancer Cells. online Available at: https://thetruthaboutcancer.com/characteristics-cancer-cells/ Accessed 10 Oct. 2018.