**Question:** True about telomeres:
(A) Made up of repeated sequence of TTAGGG
(B) Telomerase shortens it
(C) it is shortened in cancer cells,
(D) It is responsible for cell ageing

**Core Concept:**
Telomeres are repetitive nucleotide sequences located at the ends of chromosomes, primarily composed of the TTAGGG sequence. They play a crucial role in maintaining chromosome stability, preventing genomic instability, and ensuring proper DNA replication during cell division.

**Why the Correct Answer is Right:**
A) Telomeres are indeed composed of repeated sequence TTAGGG, which is the primary structure found at the ends of chromosomes. This nucleotide sequence is crucial for their function as chromosome caps.

B) Telomerase is an enzyme that adds TTAGGG nucleotides to the telomeres, counteracting their shortening during cell replication. Ensuring the maintenance of telomere length is vital for cellular longevity and genomic stability.

C) Telomere shortening occurs in cancer cells due to the lack of telomerase activity or dysfunction. This leads to genomic instability and cellular immortality, which is a hallmark of cancer cells.

D) While telomere shortening contributes to cellular senescence and aging, it is not the primary cause of cell aging. Other factors, such as oxidative stress, DNA damage, and immune system activation, also play significant roles in the aging process.

**Why Each Wrong Option is Incorrect:**
A) While TTAGGG is the primary sequence, the question suggests that telomeres are "made up of," which is not entirely accurate. They are composed of, but not solely made up of, this sequence.

B) Although telomerase is an enzyme responsible for maintaining telomere length, the question implies that it "shortens" telomeres, which is incorrect. Telomerase actually adds TTAGGG nucleotides to the telomeres, preventing their progressive shortening.

D) While telomere shortening is associated with cellular senescence and aging, it is not the sole cause. The question suggests that telomeres are the "cause" of aging, which is not the case. Other factors contribute to the aging process, as mentioned above.

**Clinical Pearls:**
1. Understanding the role of telomeres and telomerase is essential for grasping the basics of cellular aging and genomic stability.
2. Knowledge of telomere shortening in cancer cells is relevant for studying the molecular mechanisms underlying genomic instability and immortalization in cancer.
3. Recognizing the contribution of other factors to aging, such as oxidative stress and DNA damage, helps students appreciate the complexity of the aging process and its multifactorial nature.