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BIO NMDCAT Structure of DNA
nmdcat.online July 3, 2026

88. A human genetic disease is caused by an expansion of a trinucleotide repeat (CAG) within the coding exon of a specific gene. During translation, this expansion yields an elongated tract of glutamine residues within the protein, leading to aggregation and neurodegeneration. This pathology is characteristic of

A. Sickle cell anemia
B. Huntington's disease
✓
C. Beta-thalassemia
D. Cystic fibrosis

📝 Explanation

Huntington's disease is a classic trinucleotide repeat disorder where a CAG expansion in the HTT gene produces a toxic, polyglutamine-expanded huntingtin protein.

📖 Additional Information

  • Sickle cell anemia
  • Huntington's disease
  • Beta-thalassemia
  • Cystic fibrosis

Huntington's disease is a classic trinucleotide repeat disorder where a CAG expansion in the HTT gene produces a toxic, polyglutamine-expanded huntingtin protein.

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87. A synthetic oligonucleotide is designed with a high concentration of methylated cytosine bases (5-methylcytosine) in a region of repeating CG steps. Under high salt laboratory conditions, this specific DNA fragment undergoes a structural transition from a right-handed B-form helix into a left-handed conformation characterized by a zigzag backbone geometry. This alternative structure is

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89. The introduction of a chemical agent that intercalates flat aromatic rings directly between adjacent base pairs along the DNA double helix disrupts its geometry by increasing the vertical distance between base pairs from 0.34 nm to 0.68 nm. This alteration will directly induce

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