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Chapter 24: Problem 22

Which human cell types possess telomerase activity? What characteristic of cancer is promoted by expression of telomerase? What concerns does this pose for medical therapies involving stem cells?

Short Answer

Expert verified
Telomerase is active in germ, stem, and some white blood cells; it aids cancer cell immortality. Stem cell therapies risk cancer due to telomerase activity.

Step by step solution

01

Understanding Telomerase Activity in Cells

Telomerase is an enzyme that adds repetitive nucleotide sequences to the ends of chromosomes, maintaining the length of telomeres. In humans, telomerase activity is found in certain cell types, primarily germ cells, stem cells, and some white blood cells. These cells maintain telomere length to ensure stability and longevity of the genetic material during divisions.
02

Role of Telomerase in Cancer

Cancer cells often activate telomerase, which is usually inactive in most somatic cells, allowing them to replicate indefinitely. This activity helps the cancer cells avoid senescence and apoptosis, leading to sustained cell division and tumor growth. Thus, the expression of telomerase is a hallmark of cancer's self-sufficiency in growth signals and replicative immortality.
03

Challenges in Stem Cell Therapies

Stem cells naturally have telomerase activity to retain their ability for self-renewal and differentiation. However, this can be a concern in medical therapies because if stem cells are improperly regulated, they could potentially become cancerous. The risk of developing cancers, due to their potential to bypass growth control mechanisms, is a critical consideration when designing stem cell-based treatments.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Telomerase Activity
Telomerase is a special enzyme that is like a protective agent for chromosomes. Imagine the chromosomes as shoelaces, and at the tips, you have telomeres, which are like the plastic tips of the shoelaces. Telomerase helps keep these tips intact by adding more pieces to them as cells divide. In human cells, telomerase mainly works in germ cells, stem cells, and some white blood cells.
These cells need to divide many times, so they use telomerase to keep the telomeres long and healthy, ensuring smooth cell division. Without telomerase activity, the telomeres would get too short, leading to cell damage or cell death.
Cancer Cell Replication
Cancer cells have a clever trick up their sleeves: they hijack telomerase. Normally, most of our body's cells don't have active telomerase, so they age and eventually die. However, cancer cells turn telomerase back on, allowing them to avoid the normal aging process.
This means cancer cells can keep dividing without limits, forming tumors and spreading throughout the body. This ability, helped along by telomerase, makes cancer cells difficult to stop once they start growing. The continued activation of telomerase is a major reason why cancer cells can seem to 'live forever' and spread uncontrollably.
Stem Cell Therapy Risks
Stem cell therapy holds great promise in medicine because stem cells can become any cell type needed for repair. They possess telomerase activity to keep renewing themselves and differentiate into other cell types. However, the catch is that this same property poses a risk.
If stem cells aren't carefully managed, they might start dividing uncontrollably due to their active telomerase. This could lead to unexpected growths or tumors, akin to cancer. So, one major challenge with using stem cells in therapies is ensuring they remain in check and do not grow unchecked. This requires precise regulation and monitoring to harness their benefits safely.

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Most popular questions from this chapter

Ninety percent of cancer deaths are caused by metastatic rather than primary tumors. Define metastasis. Explain the rationale for the following new cancer treatments: (a) batimastat, an inhibitor of matrix metalloproteinases and of the plasminogen activator receptor, (b) antibodies that block the function of integrins, integral membrane proteins that mediate attachment of cells to the basement membrane and extracellular matrices of various tissues, and (c) bisphosphonate, which inhibits the function of osteoclasts. Osteoclasts are cells that digest bones, for example, in remodeling during growth or healing. They can be recruited to a bone-digesting task by signals from other cells. (d) What is the importance of the EMT during metastasis?

Explain the concept of loss of heterozygosity (LOH). Why do most cancer cells exhibit LOH of one or more genes? How does failure of the spindle assembly checkpoint lead to loss of heterozygosity?

Despite differences in origin, cancer cells have several features in common that differentiate them from normal cells. Describe these.

Because of oxygen and nutrient requirements, cells in a tissue must reside within \(100 \mu \mathrm{m}\) of a blood vessel. Based on this information, explain why many malignant tumors often possess gain-of-function mutations in one of the following genes: \(\beta F G F, T G F \alpha,\) and \(V E G F\)

Many malignant tumors are characterized by the activation of one or more growth-factor receptors. What is the catalytic activity associated with transmembrane growthfactor receptors such as the EGF receptor? Describe how the following events lead to activation of the relevant growthfactor receptor: (a) expression of the viral protein gp55, (b) point mutation that converts a valine to glutamine within the transmembrane region of the Her2 receptor.
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