Q.13 The repeat sequence of telomere in humans is
(A) 5′-TATAAT-3′
(B) 5′-TTAGGG-3′
(C) 5′-GGGCCC-3′
(D) 5′-AAAAAA-3′
Answer: (B) 5′-TTAGGG-3′
The repeat sequence of telomeres in humans is 5′-TTAGGG-3′, repeated thousands of times at chromosome ends.
Option Analysis
Option (A) 5′-TATAAT-3′ represents a TATA box promoter sequence involved in transcription initiation, not telomere structure.
Option (B) 5′-TTAGGG-3′ matches the conserved G-rich hexanucleotide repeat on the G-strand of human telomeres, essential for end protection and telomerase binding.
Option (C) 5′-GGGCCC-3′ resembles CpG islands in gene promoters but lacks the TTAGGG specificity for human telomeres.
Option (D) 5′-AAAAAA-3′ denotes poly-A tails on mRNA for stability, unrelated to chromosomal telomere repeats.
The human telomere repeat sequence 5′-TTAGGG-3′ forms protective caps at chromosome ends, preventing DNA degradation and fusion during replication. This hexanucleotide repeat, present in tandem arrays of 5,000–15,000 units, shortens with each cell division, linking to aging and cancer when maintained by telomerase. Understanding this sequence is crucial for biotechnology researchers studying genetic stability, as in your work on molecular biology and enzyme kinetics.
Telomere Structure Basics
Human telomeres feature the G-rich 5′-TTAGGG-3′ on the 3′ overhang and complementary 5′-CCCTAA-3′ on the C-strand. Shelterin proteins bind these repeats to form T-loops, shielding ends from repair machinery. In plants like Arabidopsis, it’s TTTAGGG, but vertebrates uniformly use TTAGGG.
Why Other Options Fail
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5′-TATAAT-3′: Transcription promoter, not chromosomal.
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5′-GGGCCC-3′: Promoter CpG motif, no telomere role.
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5′-AAAAAA-3′: mRNA poly-A, post-transcriptional.
Only TTAGGG enables telomerase extension via its RNA template.
Research Relevance
For graduate-level biotech studies, telomere repeats influence replication timing and mutagenesis, as seen in somatic cells. Techniques like PCR amplify these for telomere length assays in immunology and genetic engineering experiments.
