Q.Collect 5 examples of palindromic DNA sequences by consulting your teacher. Better try to create a palindromic sequence by following base-pair rules.

Palindromic DNA sequences are those that read the same on both strands when you read one strand in the 5' to 3' direction and the other strand also in the 5' to 3' direction. This happens because the sequence on one strand is identical to its complementary strand when both are read in the same direction. The key is that the base-pairing rules (A with T, and G with C) must hold, so the sequence on one strand determines the sequence on the other.

To create your own palindromic sequence, start by writing a short stretch of DNA on one strand, say 5' to 3'. Then, write its complementary strand in the 3' to 5' direction. Now, reverse the complementary strand so it reads 5' to 3'. If this reversed complementary strand matches your original strand exactly, you have a palindrome. For example, if you start with 5' GAATTC 3', its complement is 3' CTTAAG 5'. Reversing that complement gives 5' GAATTC 3' — a perfect mat …

Let’s begin with the idea. In everyday language, a palindrome is a word or phrase that reads the same forwards and backwards — like “MADAM” or “RACECAR.” DNA, being a double-stranded molecule, has its own version of this. A palindromic DNA sequence is one where the sequence of bases on one strand, when read from the 5' end to the 3' end, is exactly identical to the sequence on the complementary strand when it is also read from its 5' end to its 3' end. This is not just a neat trick of nature; it is a structurally important feature, especially in the context of restriction enzymes — the molecular scissors used in genetic engineering. Many restriction enzymes recognise and cut at specific palindromic sequences, which is why this concept is central to your NCERT syllabus.

To understand how to create one, you must first recall the base-pairing rules: Adenine (A) always pairs with Thymine (T), and Guanine (G) always pairs with Cytosine (C). Now, imagine you write a short sequence on one strand, say 5' – GAATTC – 3'. To get the complementary strand, you would write the partner bases: C for G, T for A, A for T, T for A, G for C, and C for G. That gives you 3' – CTTAAG – 5'. But here is the crucial step: to check for a palindrome, you must read that complementary strand in the 5' to 3' direction. So you flip it: 5' – GAATTC – 3'. It is exactly the same as the original strand. That is a palindrome.

Alternative Approach: A Faster "Outside-In Pairing" Shortcut

Writing out the full complementary strand and then reversing it (as in the main answer)

always works, but there is a quicker mental shortcut for both checking and constructing

palindromes.

Step 1: Understand the shortcut rule.

For a sequence to be palindromic, the base at position 1 (from the 5' end) must be the

Watson-Crick complement of the base at the LAST position; the base at position 2 must be

the complement of the second-last position; and so on, working inward from both ends.

Step 2: Apply it to check an existing sequence, e.g. GAATTC.

Position 1 (G) vs position 6 (C): G pairs with C -- match.

Position 2 (A) vs position 5 (T): A pairs with T -- match.

Position 3 (A) vs position 4 (T): A pairs with T -- match.

All three outside-in pairs check out, so GAATTC is palindromic -- confirmed without

writing out a second strand at all.

Step 3: Apply it to construct a new one.

Pick any base for position 1, say C; position 6 must then be G. Pick any base for …