Q.35 The functions of telomeres is :

1. Protect intact eukaryotic chromosomes from improper fusion or degradation
2. Attack the intact eukaryotic chromosomes at the centromeric region
3. Degrade the intact eukaryotic chromosome
4. Protect the intact chromosomes from histone proteins

   Telomeres Protect Eukaryotic Chromosomes from Fusion and Degradation

   Telomeres function to protect intact eukaryotic chromosomes from improper fusion or degradation at their ends, making the first option correct. These repetitive DNA-protein caps prevent chromosome ends from being recognized as DNA damage.​

   Introduction

   The functions of telomeres center on protecting chromosome ends from fusion, degradation, and DNA repair activation. Composed of TTAGGG repeats and shelterin proteins, telomeres form protective t-loops maintaining genomic stability. This guide analyzes each option for cell biology exam precision.

   Option Analysis

   Telomere structure: 5′-TTAGGG-3′ repeats (5-15 kb humans) + shelterin complex (TRF1/2, POT1, TIN2, Rap1, TPP1).​

   • Protect intact eukaryotic chromosomes from improper fusion or degradation: Correct. Telomeres prevent end-to-end fusions (dicentric chromosomes) and exonuclease degradation via t-loop formation; shelterin inhibits NHEJ/ATM signaling.

   • Attack the intact eukaryotic chromosomes at the centromeric region: Incorrect. Centromeres (kinetochore assembly) are internal; telomeres reside at ends. No “attack” function exists.​

   • Degrade the intact eukaryotic chromosome: Incorrect. Opposite role—telomeres protect from degradation. Progressive shortening triggers senescence, not active degradation.​

   • Protect the intact chromosomes from histone proteins: Incorrect/misleading. Histones package all chromatin (nucleosomes); telomeres use variant histone H3 (CENP-A centromeres, H3.1 telomeres) with shelterin, not “protection from histones.”​

   Telomere Protection Mechanism

   T-loop formation:

   text

   Linear end → 3' G-overhang invasion → D-loop → T-loop (TRF2-mediated)
POT1 protects ssDNA overhang → Shelterin suppresses DDR


   Critical functions:

   Protection Role	Mechanism	Consequence of Failure
   End-to-end fusion	Shelterin blocks NHEJ	Dicentric bridges, breakage-fusion-bridge cycle
   Exonuclease block	POT1 binding	Progressive telomere erosion
   DDR suppression	TRF2 inhibits ATM	Senescence/apoptosis ​

   Telomerase maintenance: hTERT + hTERC adds TTAGGG; stem cells/germ cells (~50-100 bp/cell division).

   Pathological Implications

   • Short telomeres: Dyskeratosis congenita, idiopathic pulmonary fibrosis

   • Telomerase activation: 90% cancers (immortality mechanism)

   • Critically short: Chromosome end-joining → aneuploidy

   Exam Relevance

   GATE Life Sciences: “TELomeres TELeprotect ENDs” (fusion/degradation). Classic distractor: centromere confusion. Visualize: T-loop = telephone cord protecting frayed end.​