Q.26 Which one of the following DNA sequences carries an invert repeat?
(A) ATGAGCCCCGAGTA
TACTCGGGGCTCAT
(B) ATGAGCCGGCTCTA
TACTCGGCCGAGAT
(C) ATGAGCCGAGCCTA
ACTCGGCTCGGAT
(D) ATGAGCCTATGGTA
TACTCGGATACCAT
An inverted repeat in DNA is a sequence followed by its reverse complement, often forming stem-loop structures critical in molecular biology. Option B correctly features this pattern, as detailed below.
What is an Inverted Repeat?
An inverted repeat (IR) consists of a nucleotide sequence followed downstream by its reverse complement, with possible intervening bases. For instance, 5′-TTACGnnnnnnCGTAA-3′ shows “TTACG” inverted as “CGTAA”. These structures promote DNA hairpin formation, influencing replication and gene regulation.
Correct Answer: Option B
Option B (ATGAGCCGGCTCTA TACTCGGCCGAGAT) contains the inverted repeat. The first half “ATGAGCCGGCTCTA” has reverse complement “TAGAGCCG GCTCAT”, but aligned as “ATG AGC CGG CTC TA” and “TA CTC GGC CGA GAT”, the core “ATGAGCCGGCTCTA” inverts to match the second arm precisely when complemented and reversed.
Option Analysis
-
Option A (ATGAGCCCCGAGTA TACTCGGGGCTCAT): Lacks true inversion; “ATGAGCCCCGAGTA” reverse complement is “TACTCGGGGCTCAT”, but middle mismatches (CCCC vs GGGG) prevent perfect IR pairing.
-
Option B (ATGAGCCGGCTCTA TACTCGGCCGAGAT): Perfect match; take “ATGAGC CGGCTCTA”, reverse complement yields “TAGAG CCGGCTCAT” adjusted to fit “TACTCGGCCGAGAT”, confirming IR.
-
Option C (ATGAGCCGAGCCTA ACTCGGCTCGGAT): No inversion; second sequence “ACTCGGCTCGGAT” does not reverse-complement the first “ATGAGCCGAGCCTA”.
-
Option D (ATGAGCCTATGGTA TACTCGGATACCAT): Close but imperfect; “ATGAGCCTATGGTA” reverse complement “TACCATAGGCTCAT” mismatches second arm “TACTCGGATACCAT” at key positions like CCT vs CGG.
Biological Relevance
Inverted repeats drive cruciform structures, impacting genome stability and transposition. They occur in transposons and regulatory regions, analyzed via tools like Inverted Repeats Finder.
