Explain with an example the 'palindromic nucleotide sequence' in the formation of recombinant DNA.

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Q. Explain with an example the 'palindromic nucleotide sequence' in the formation of recombinant DNA.

Manipur CohsemCOHSEM Manipur Higher Secondary Board 2023Subjective· 2mImportance★★★★★

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Concept understanding — Palindromic DNA Sequences

Imagine you are looking in a mirror. Your right hand becomes the reflection’s left hand, and your left becomes its right. The word “MALAYALAM” reads the same forwards and backwards. That mirror-like symmetry is the core idea behind a palindromic DNA sequence.

In everyday language, a palindrome is a word, phrase, or number that reads identically in both directions. DNA is a long, double-stranded molecule — think of it as a twisted ladder. Each rung of the ladder is made of two chemical letters (called bases) that pair up in a very specific way: A always pairs with T, and C always pairs with G.

Now, a palindromic DNA sequence is a stretch of DNA where the sequence of letters on one strand reads exactly the same as the sequence on the opposite strand, but in the opposite direction. Because the two strands run in opposite directions (biologists call this “antiparallel”), the palindrome is not just a simple mirror of letters — it is a mirror of the pairing.

Note

In textbooks, you will often see a palindromic sequence written like this:

5' – GAATTC – 3'

3' – CTTAAG – 5'

Notice that if you read the top strand left to right (GAATTC) and then read the bottom strand right to left (also GAATTC), you get the same sequence. That is the palindrome.

Why does this matter? Because nature uses these sequences as recognition sites. Special proteins — especially restriction enzymes — are designed to find these exact palindromic stretches and cut the DNA at that precise spot. This is the foundation of genetic engineering:

Restriction enzymes act like molecular scissors. They only cut at their specific palindromic sequence.
Because the sequence is the same on both strands, the cut produces either “blunt” ends or “sticky” ends (short, single-stranded overhangs). Sticky ends are particularly useful because they can easily join with another piece of DNA that has the complementary sticky end — like two puzzle pieces.
This allows scientists to cut DNA from one organism and paste it into the DNA of another, creating recombinant DNA.

Important

The NCERT textbook (Class 12 Biology, Chapter 11) explicitly states: “Restriction enzymes cut the strand of DNA a little away from the centre of the palindromic site, but between the same two bases on the opposite strands.” This means the cut is not perfectly in the middle — it is offset, which creates the sticky ends. …

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Palindromic DNA sequences are the specific 'address labels' that restriction enzymes recognise and cut, creating matching sticky ends used to build recombinant DNA.

A palindromic nucleotide sequence is a base sequence in double-stranded DNA that reads identically on both strands when each strand is read in the 5'→3' direction. For example:

5'-G A A T T C-3'

3'-C T T A A G-5'

Reading the top strand 5'→3' gives GAATTC; reading the bottom strand 5'→3' (i.e., right to left as drawn) also gives GAATTC — the two reads are identical, which is the defining property of a palindrome. Restriction endonucleases (e.g., EcoRI, isolated from E. coli) specifically recognise such palindromic sequences and cleave the DNA backbone at or near a fixed point within them. Because the enzyme cuts both strands at symmetric positions within the palindrome, it typically leaves short single-stranded overhangs called 'sticky ends', which are complementary to any other DNA fragment cut by the same enzyme. In recombinant DNA technology, this property is exploited: the vector and the foreign ('insert') DNA are both cut with the sa …

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2026Set ANNUAL1 mark
$Q. The sequence of base pairs in a double-stranded DNA or RNA molecule that reads the same in forwards and backward on each strand is called _________ nucleotide sequence.$
›Reveal solutionSolution
The blank is palindromic — a base-pair sequence that reads the same in the 5'→3' direction on both strands, which is the recognition site for restriction endonucleases.

In the CBSE/NCERT Biotechnology: Principles and Processes chapter, restriction enzymes cut DNA at specific palindromic sequences. For example:

5' G A A T T C 3' 3' C T T A A G 5'

…
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CBSE 2019Set HE1 mark
$Q. Match the following: Column A item 'Palindromic' with the correct term from Column B:$
(1) Big-Bang
(2) D.N.A.
(3) Tansley
(4) Green revolution
(5) Male-sterility.
›Reveal solutionSolution

'Palindromic' matches with 'D.N.A.' — palindromic sequences are specific nucleotide sequences found within DNA.

A palindromic sequence in DNA is a sequence of base pairs that reads the same in the 5′→3′ direction on both strands (e.g., GAATTC / CTTAAG). Restriction endonucleases recognise such short palindromic sequences within a DNA molecule and cleave the DNA at or near them, which is fundamental …

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CBSE 2017Set ANNUAL1 mark
$Q. Sequences of base pairs in DNA that reads the same on both the strands when the orientation of reading is kept the same are called ________ sequences.$
›Reveal solutionSolution

A DNA sequence that reads identically on both strands (in the same 5'→3' direction) is called a palindromic sequence — the sites recognised and cut by restriction endonucleases.

In ordinary usage a palindrome is a word/phrase that reads the same forwards and backwards (e.g. 'MALAYALAM'). In molecular biology, a palindromic sequence in double-stranded DNA is a base-pair sequence that reads the same on both strands when each is read in the 5'→3' direction — for example:

5'-GAATTC-3'

3'-CTTAAG-5'

…

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Q.Explain with an example the 'palindromic nucleotide sequence' in the formation of recombinant DNA.

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