Question

If a DNA strand contains the sequence 5ʹ-ATTCCGGATCGA-3ʹ, which of the following is the sequence of the complementary strand of DNA?
5ʹ-TAAGGCCTAGCT-3ʹ
5ʹ-ATTCCGGATCGA-3ʹ
3ʹ-TAACCGGTACGT-5ʹ
5ʹ-TCGATCCGGAAT-3ʹ

Answer 1

Answer:

5ʹ-ATTCCGGATCGA-3ʹ

Explanation:

In a double-stranded DNA, two strands are held together with the help of hydrogen bonds between nitrogenous bases and the two strands are anti-parallel, means one strands runs in 5' to 3' direction, while another strand runs in 3' to 5' direction.

According to complementary base pairing rule, adenine makes bonds with thymine and thymine makes bond with adenine; similarly, guanine makes bonds with cytosine and cytosine makes bonds with guanine.  

Thus, the complementary base pairing rule, complementary sequence for given DNA sequence would be:

5ʹ-TCGATCCGGAAT-3ʹ

3ʹ-AGCTAGGCCTTA-5ʹ, which can be also written as

5ʹ-ATTCCGGATCGA-3ʹ.

Thus, the correct answer is 'second option.'

Answer 2

Answer:

3ʹ-TAACCGGTACGT-5ʹ

Explanation:

DNA is a molecule located in the cell nucleus and formed by two strands in the form of a double helix. It is responsible for storing all genetic information that defines the characteristics of each living organism.

The two complementary strands that make up this molecule are composed of a sequence of nucleotides, which are molecules composed of a phosphate group, a sugar (pentose) and a nitrogenous base that can be: Adenine (A), Thymine (T), Guanine (G) and Cytosine (C).

Nitrogenous bases are always organized in pairs: Adenine with Thymine (A-T) and Cytosine with Guanine (C-G). Therefore, we can conclude that if one of the DNA strands has the 5ʹ-ATTCCGGATCGA-3ʹ base sequence, the complementary strand will have the 3ʹ-TAACCGGTACGT-5ʹ base sequence.