Telomeres: Videos & Practice Problems

Telomeres are non-coding DNA sequences located at the ends of eukaryotic chromosomes, crucial for protecting genetic information during cell division. With each replication, telomeres shorten, which is linked to aging and signals cells to stop dividing. However, some cells, like germ and cancer cells, express telomerase, an enzyme that maintains telomere length, allowing continuous division. This mechanism is significant in understanding cellular aging and cancer proliferation, highlighting the balance between normal cellular function and pathological growth.

Telomeres

Telomeres are essential structures found at the ends of eukaryotic chromosomes, composed of non-coding DNA that consists of repeating sequences. Unlike prokaryotic chromosomes, eukaryotic chromosomes rely on telomeres to protect their genetic information during cell division. Each time a cell undergoes DNA replication, telomeres shorten, which has been associated with the aging process. This gradual shortening serves as a biological clock, signaling normal cells to cease division when telomeres become critically short, ultimately leading to cell death.

In a typical eukaryotic chromosome, the coding DNA is located in the internal regions, while telomeres are positioned at the tips. As cells replicate, the chromosomes progressively shorten, indicating that longer telomeres are characteristic of younger cells, whereas shorter telomeres are indicative of older cells. This relationship between telomere length and cellular age highlights the role of telomeres in the aging process.

Interestingly, some cells express an enzyme known as telomerase, which can counteract telomere shortening. Telomerase catalyzes the addition of DNA sequences to the telomeres, effectively maintaining their length. This enzyme is predominantly found in germ cells, which are precursors to gametes, and in many cancer cells. The presence of telomerase allows these cells to bypass the normal signals that would halt cell division due to telomere shortening, enabling continuous proliferation. Understanding the dynamics of telomeres and telomerase is crucial for insights into aging and cancer biology.

What are telomeres?

• A. The region of DNA that holds two sister chromatids together.
• B. Enzymes that elongate a new DNA strand during replication.
• C. The sites of origin of DNA replication.
• D. The ends of linear chromosomes.

Answer: (D)

Which of the following effects might be caused by reduced or very little active telomerase activity?

• A. Cells may become cancerous.
• B. Telomere lengthens in sex cells.
• C. Cells age and begin to lose function.
• D. Cells continue to function normally.

Answer: (C)

Which of the following types of cells are affected most by telomere shortening?

• A. Prokaryotic cells only.
• B. Eukaryotic cells only.
• C. Prokaryotic and eukaryotic cells.
• D. Animal cells only.

Answer: (B)

Telomere shortening puts a limit on the number of times a cell can divide. Research has shown that telomerase can extend the life span human cells. How might adding telomerase affect cellular aging?

• A. Telomerase will speed up the rate of cell division.
• B. Telomerase stops telomere shortening and slows or stops cellular aging.
• C. Telomerase shortens telomeres, which slows or stops cellular aging.
• D. Telomerase would have no effect on cellular aging.

Answer: (B)

Here’s what students ask on this topic:

What are telomeres and why are they important?

Telomeres are non-coding DNA sequences located at the ends of eukaryotic chromosomes. They consist of repetitive nucleotide sequences that protect the chromosome ends from deterioration or fusion with neighboring chromosomes. Telomeres are crucial because they safeguard the genetic information during cell division. Each time a cell divides, the telomeres shorten, which is linked to the aging process. When telomeres become too short, it signals the cell to stop dividing, leading to cellular aging and eventual cell death. This mechanism helps maintain genetic stability and prevents the loss of essential genetic information.

How does telomerase affect telomere length?

Telomerase is an enzyme that adds repetitive nucleotide sequences to the ends of telomeres, effectively lengthening them. This enzyme is particularly active in germ cells, which are the precursor cells to gametes (sex cells), and in cancer cells. By maintaining telomere length, telomerase allows these cells to continue dividing without the usual telomere shortening that signals cell division to stop. This continuous division is crucial for germ cells to produce gametes and for cancer cells to proliferate uncontrollably. Understanding telomerase's role is essential for insights into cellular aging and cancer treatment strategies.

What is the relationship between telomere shortening and aging?

Telomere shortening is closely linked to the aging process. Each time a cell divides, its telomeres shorten. Over time, as telomeres become critically short, they signal the cell to stop dividing, leading to cellular senescence or apoptosis (cell death). This progressive shortening of telomeres contributes to the aging of tissues and organs, as the regenerative capacity of cells diminishes. Therefore, telomere length is considered a biomarker of cellular aging, and understanding this relationship is crucial for studying age-related diseases and potential anti-aging therapies.

Why do cancer cells maintain their telomere length?

Cancer cells maintain their telomere length primarily through the activity of the enzyme telomerase. By expressing high levels of telomerase, cancer cells can continuously add repetitive nucleotide sequences to their telomeres, preventing them from shortening. This allows cancer cells to bypass the normal cellular aging process and continue dividing indefinitely. The ability to maintain telomere length is a key factor in the uncontrolled proliferation of cancer cells, making telomerase a significant target for cancer research and potential therapeutic interventions.

How do telomeres differ between eukaryotic and prokaryotic cells?

Telomeres are specific to eukaryotic cells and are found at the ends of eukaryotic chromosomes. They consist of non-coding, repetitive DNA sequences that protect the chromosome ends during cell division. In contrast, prokaryotic cells, which include bacteria and archaea, typically have circular chromosomes and do not possess telomeres. The circular nature of prokaryotic chromosomes eliminates the need for telomeres, as there are no ends to protect. This fundamental difference highlights the distinct mechanisms of chromosome maintenance and replication between eukaryotic and prokaryotic cells.