Telomere Composition Human telomeric DNA repeats are typically rich in which nucleotide base?

Introduction / Context:
Telomeres cap chromosome ends with tandem repeats (e.g., in humans, the repeat is TTAGGG). Their nucleotide composition influences secondary structures (e.g., G-quadruplexes) and telomerase activity.

Given Data / Assumptions:

• Human telomeric repeat sequence: TTAGGG (5′→3′).
• G-richness promotes unique higher-order DNA conformations.

Concept / Approach:
Examine the canonical repeat: TTAGGG contains two thymines, one adenine, and three guanines, making the sequence guanine-rich. This G-rich nature is conserved across many species and is functionally relevant for binding proteins and telomerase substrate recognition.

Step-by-Step Solution:

Verification / Alternative check:
Biophysical studies show G-quadruplex formation in telomeric DNA, a phenomenon dependent on G-rich sequences.

Why Other Options Are Wrong:

• Adenine and thymine are present but not dominant.
• Cytosine is part of the complementary strand, not the overhang; not the defining enrichment.
• Uracil is not present in DNA.

Common Pitfalls:
Confusing RNA telomerase template with DNA telomere sequences; assuming A/T-rich repeats.

Final Answer:
Guanine