Question

True replication of DNA is possible due to
A. Hydrogen bonding
B. Phosphate backbone
C. Complementary base pairing rule
D. None of the above

Answer 1

Hint: The process of making two similar DNA copies from a single DNA available is known as DNA replication. Every cell that divides replicates its DNA so that DNA can be transferred to the daughter cells.

Complete answer:
DNA has a double helical structure that is made up of complementary DNA strands. When DNA starts to replicate these strands separate and act as templates on which new DNA strands will be developed. DNA replication starts at specific regions of the cell also known as origin of replication or ‘ori’ during the synthesis phase of interphase. The strand of DNA is double helix and unwound by helicase enzyme due to which a replication form is made. Another enzyme DNA polymerase is used to extend the DNA strand.

Steps of DNA replication include:
-Initiation – Replication is initiated at specific points known as origin of replication which recruit enzymes to unwind the DNA forming a replication fork. An enzyme called DNA primase from RNA primer which aids in activating DNA polymerase.
-Elongation – New daughter DNA strand is synthesised by DNA polymerase by secretion of complementary sequences and that is how the strand elongates. DNA is synthesised on the 5’ to 3’ strand by DNA polymerase. Template strand is 3’ to 5’ and is known as the leading strand as it is continuous whereas the other strand is non continuous and known as the lagging strand. The lagging strand forms Okazaki fragments which are joined by DNA ligase.
-Termination – Elongation stops when the template DNA cannot be replicated any further or two replication forks merge into each other.
So the DNA replication is possible only by the complementary base pairing of the nucleotides Adenine with thymine and guanine with cytosine. These nucleotides are bound to each other with the help of hydrogen bonds and the phosphate backbone is meant to provide support to the DNA molecule.

Hence, the correct answer is option (C).

Additional information:
As one strand of the DNA helical structure is used as a template for the next DNA molecule that makes it semiconservative as a part of the previous DNA is preserved and passed onto the next.
Replication of DNA is completed before a cell undergoes mitosis.
Three types of DNA polymerase are being used – DNA polymerase I (It is meant for DNA repair), DNA polymerase II (Responsible for the extension of primer) and DNA polymerase III (used for in vivo DNA replication).

Note: During replication the entire genome of a cell is duplicated into new cells and DNA polymerase being the most important enzyme required in this process adds nucleotides only from 3’ to 5’ direction and never in the opposite direction.