Q.55 Given below are two statements :
Statement I :
In total, only about 1.5% of human DNA is coding or exon DNA, carrying information for proteins or RNA products.
However, when the much larger introns are included in the count, as much as 30% of the human genome consists of genes.
Statement II :
DNA helicase is the enzyme that increases or decreases the extent of DNA underwinding and affects the linking number.
In the light of the above statements, choose the correct answer from the options given below :
- Both Statement I and Statement II are correct
- Both Statement I and Statement II are incorrect
- Statement I is correct but Statement II is incorrect
- Statement I is incorrect but Statement II is correct
Statement I is correct, but Statement II is incorrect, as DNA helicase unwinds DNA strands while topoisomerases manage supercoiling and linking number.
Statement Analysis
Statement I: Accurate—human exons code ~1-2% of DNA for proteins/RNA, but genes (exons + introns) span ~20-30% of the genome due to large introns. [prior from PCR query, general genomics knowledge]
Statement II: Incorrect—DNA helicase unwinds double-stranded DNA by breaking hydrogen bonds during replication/transcription, creating single strands; it does not directly control DNA underwinding extent or linking number (Lk = twist + writhe). Topoisomerases (e.g., DNA gyrase, topoisomerase I/II) relieve supercoils and adjust Lk by strand passage.
Option Breakdown
-
Both correct: Wrong; II misattributes topoisomerase function to helicase.
-
Both incorrect: Wrong; I is factually right.
-
I correct, II incorrect: Correct; matches analysis above.
-
I incorrect, II correct: Wrong; I holds, II does not.
Human DNA Coding Breakdown
Human DNA coding refers to ~1.5% exons carrying protein/RNA info, while genes with introns reach 30% of genome—vital for GATE genomics. [prior knowledge] Non-coding regions dominate, regulating expression.
DNA Helicase Role
DNA helicase unwinds dsDNA at replication forks using ATP, separating strands for polymerases—not adjusting underwinding or linking number (topoisomerase task).
| Concept |
% Genome |
Key Enzyme |
Function |
| Exons (coding) |
~1.5% |
N/A |
Protein/RNA code [prior] |
| Genes (exons+introns) |
~30% |
Helicase (unwinds) |
Strand separation |
| Linking number control |
Supercoils |
Topoisomerase |
Relieves tension |
GATE Q.55 Verdict
Statement I correct, II incorrect—exon stats hold; helicase unwinds, topoisomerases handle Lk.
