Question

how to find the complementary genomic sequence of this oligonucleotides, please explain how to do find it.

Oligo 1 5’-CGCTAGGATCGAACCATACTCGGAC-3’

Oligo 2 5’-CATAGAATTTACGCATACCTAAGAT-3’

Oligo 3 5’-TACGTACGTACGCGTACGTACGTA-3’

Answer 1

Complementary genomic sequence of oligonucleotides means that we need to construct another oligonucleotide that will pair with the one in the question. This pairing occurs by following certain rules.
Purines (such as Adenine and Guanine) bind with Pyrimidines (such as Thymine and Cytosine) and as such in a specific order. So A binds with T, T with A, C with G, and G with C.
To construct the complementary genomic sequence of this oligonucleotides, simply write down the corresponding complementary alphabet in its place.
A -> T
T -> A
C -> G
G -> C

Since the strands in the question run from 5' to 3' direction, the resulting complementary strand needs to run in the opposite direction:

Oligo 1
5’-CGCTAGGATCGAACCATACTCGGAC-3’
3’ - GCGATCCTAGCTTGGTATGAGCCTG - 5’ (ANSWER)
Oligo 2
5’-CATAGAATTTACGCATACCTAAGAT-3’
3’ - GTATCTTAAATGCGTATGGATTCTA - 5’ (ANSWER)
Oligo 3
5’-TACGTACGTACGCGTACGTACGTA-3’
3’ - ATGCATGCATGCGCATGCATGCAT - 5’ (ANSWER)