Stem cells are a type of cell that has the ability to divide and renew themselves for long periods. They are found in most tissues of the body and can give rise to specialized cells. Stem cells divide in one of two ways: symmetrically or asymmetrically.
Symmetrical division results in two daughter cells that are identical to the parent cell. Asymmetrical division results in two daughter cells that are different from each other and from the parent cell. Differentiation is the process by which a stem cell becomes a more specialized cell type. During differentiation, the cell changes its shape, size, and function. After a stem cell divides, one of the two daughter cells may become a new stem cell, while the other daughter cell begins to differentiate. The new stem cell can then go on to divide and produce more stem cells, or it can differentiate into a specialized cell type. Specialized cells make up the tissues and organs of the body. They are unable to divide or renew themselves and have specific functions. For example, muscle cells contract to produce movement, and nerve cells transmit electrical signals. When a stem cell divides asymmetrically, one of the daughter cells retains the ability to divide and renew itself, while the other daughter cell begins to differentiate. This ensures that there is a constant supply of stem cells available to replace cells that are lost or damaged.
In recent years, much progress has been made in our understanding of how stem cells behave, both in the laboratory and in the body. One of the key features of stem cells is their ability to divide and give rise to new cells, a process known as self-renewal. This ability is essential for maintaining the pool of stem cells in the body throughout our lifetime. However, it has been increasingly recognized that stem cells in the body are not always ‘stemmy’, meaning they are not always able to divide and renew themselves. As we age, stem cells gradually lose their ability to self-renew and become ‘senescent’. This process is thought to contribute to the aging of tissues and the development of age-related diseases. Interestingly, it has also been shown that stem cells can become ‘senescent’ in the laboratory, even when they are growing in culture and are not exposed to the aging process. This suggests that there are factors within the stem cell itself that can cause it to lose its ability to self-renew. One factor that has been shown to influence the self-renewal of stem cells is the number of times they have divided. It is well known that as cells divide, their telomeres (the protective caps at the ends of chromosomes) become shorter.
Eventually, the telomeres become so short that the cell can no longer divide and it becomes senescent. It is thought that stem cells may have a higher threshold for telomere shortening than other cells, meaning they can divide more times before becoming senescent. However, it is also possible that stem cells may lose the ability to self-renew as a result of telomere shortening. In order to investigate this, scientists have created ‘clones’ of stem cells, which are cells that have been derived from a single parent cell. These clones have been found to have shorter telomeres than the parent cells, suggesting that they may have a reduced ability to self-renew. It is not yet clear why this is the case, but it is possible that the telomeres of stem cells are more susceptible to shortening when they are cloned. This could be due to the fact that the DNA of stem cells is more actively replicated than other cells in the body, meaning that the telomeres are more likely to be shortened with each cell division. It is also possible that the shortened telomeres in clones are a result of the fact that they are derived from a single-parent cell.
When cells divide, they do not always divide evenly, meaning that the daughter cells can end up with different amounts of DNA. This could lead to telomere shortening in the clones if the parent cell had shorter telomeres, to begin with. Whatever the reason, the fact that stem cell clones have shorter telomeres than their parent cells suggests that they may lose their ability to self-renew sooner. This could have important implications for the use of stem cells in therapy, as it may mean that the cells would need to be replaced more frequently. It is also possible that the shortened telomeres in clones are a result of the fact that they are derived from a single-parent cell. When cells divide, they do not always divide evenly, meaning that the daughter cells can end up with different amounts of DNA. This could lead to telomere shortening in the clones if the parent cell had shorter telomeres to begin with. Whatever the reason, the fact that stem cell clones have shorter telomeres than their parent cells suggests that they may lose their ability to self-renew sooner. This could have important implications for the use of stem cells in therapy, as it may mean that the cells would need to be replaced more frequently.
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Who is credited with discovering the concept of stem cells in the early 1900s?
When were human embryonic stem cells first isolated and grown in a laboratory setting?
When were induced pluripotent stem cells (iPSCs) first created?
Which of the following statements about stem cell research is NOT true?
Which of the following is NOT a potential source of stem cells for use in research and therapy?
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