Question

Repeated sequence TTAGGG AATCCC in humans is present at:

• A. Centromere
• B. Nucleolus
• C. Histones
• D. Telomere

Hint:

Human telomere repeat motif: $5'$-TTAGGG-$3'$.
Telomeres shorten with successive somatic cell divisions, acting as a biological clock for cell aging.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to locate the chromosomal region characterized by tandem repeats of the hexanucleotide sequence $5'$-TTAGGG-$3'$ in human D.

Step 2: Key Formula or Approach:
Linear chromosome ends require specialized nucleoprotein complexes consisting of short repetitive D sequences to protect genomic material from degradation and end-to-end chromosomal fusion.

Step 3: Detailed Explation:

• Structure of Telomeres: Telomeres are specialized nucleoprotein structures situated at the physical termini of eukaryotic linear chromosomes.

• Human Telomeric Sequence: Human telomeres consist of hundreds to thousands of tandem repeats of the hexamer motif $5'$-TTAGGG-$3'$ on one strand paired with its complementary strand $3'$-AATCCC-$5'$.

• Function: Telomeres resolve the "end-replication problem" caused by the ibility of D polymerase to fully replicate the extreme $5'$ end of linear lagging strands.

• Telomerase Enzyme: The ribonucleoprotein enzyme telomerase extends these hexameric sequences using an interl R template.

• Comparison with Other Structural Regions:

• Centromere: Contains satellite D (e.g., alpha satellite repeats) responsible for kinetochore assembly.

• Nucleolus: Nuclear domain surrounding ribosomal R (rR) gene repeats.

• Histones: Basic proteins involved in packaging D into nucleosomes, not specific repetitive D regions.

Step 4: Fil Answer:
The repeating tandem sequence $5'$-TTAGGG-$3'$ is localized specifically at human telomeres.