Question

A strand of DNA has the following sequence: 5'-ACTGCCTATGCT-3'.What is the complementary strand that will be formed when the molecule undergoes replication during the M phase of the cell cycle?
A. 5'-TGACGGATACGA-3'
B. 3'-TGACGGATACGA-5'
C. 5'-ACTGCCTATGCT-3'
D. 3'-ACTGCCTATGCT-5'
E. 3'-UGACGGAUACGA-5'

Answer 1

Hint:DNA is composed of complementary combinations of nitrogenous bases which occur in pairs. These are complementary to each other such as G-C and A-T. While A forms a double bond with T, G forms a triple bond with C. These are further joined with each other through a sugar-phosphate backbone. The bond strength gives the DNA its double helix shape.

Complete answer:
In Deoxyribonucleic acid i.e. DNA is the double helix inheritable structure in which the following pairing takes place:
Guanine (G) pairs with Cytosine (C)
Adenine (A) pairs with Thymine (T)
Further, DNA replicates in the M phase.
Then complementary nucleotides for each base pair will be added as follows:
A – T
T - A
G - C
C - G
Now, since the template strand here is 5'-ACTGCCTATGCT-3' further replication occurs in 5'-3' direction, so the complementary strand will be formed in 3'-5' direction.
Therefore the sequence of complementary strand formed after replication will be:
3'-TGACGGATACGA-5'

So, the correct answer will be 3'-TGACGGATACGA-5' i.e. option: B)

Additional information:
The process of DNA replication is semi-conservative. Each one of the parent DNA strands acts as a template from which new strands are coded. The newly formed DNA strands have similar nucleotide sequences and are further inherited by the two daughter cells upon equal division.

Note: The polarity of template strand is 5'-3' and coding strand has a polarity of 3'-5'. It consists of anticodons while the coding strand has only codons. It is a template strand that takes part in the process of transcription.