Question

Which single-stranded nucleic acid could form a hairpin structure? Select one:

a. 5’ TTTGCGATACTCATCGCATT 3’

b. 5’ TTTGCGATACTCACACTATT 3’

c. 5’ TTTGCGATACTCTGCGATTT 3’

d. All of the sequences above could form a hairpin loop.

e. None of these sequences could form a hairpin loop.

Answer 1

option-a 5’ TTTGCGATACTCATCGCATT 3’

Hair pin or a stem loop structure of nucleic acid is mostly found in single stranded RNA and sometimes in DNA too. The formation of hairpin structure is due to the intramolecular basepairing of the nucleotides within the single strand. The strand gets folded by basepairing forming a hair pin structure

To make this clear, Take for ex-

option- a. 5’ TTTGCGATACTCATCGCATT 3

The step to check if the sequence can form hairpin structure is to check if the first base and last base is complementary to each other

the first base is T and the last base is T, so this cannot basepair with each other

The second base is T and the second last base is also T, so this cannot basepair with each other

But the third base T is complementary to the third last base A

The fourth base G is complementary to the fourth last base C

from this till the 8th base we can see that they are complementary to each

The 9th, 10th, 11th, 12th base are not complementary to each other. This structure forms the loop in the hairpin shape.

I have attached an image to make this understand much clearer!

in other options such as opt-b- 5’ TTTGCGATACTCACACTATT 3’ and

opt-c- 5’ TTTGCGATACTCTGCGATTT 3’

We can see that the bases from the first and the last do not form intramolecular pairing because they are not complementary to each other.