Replication of DNA is characterised by:

(A) The direction of replication is 5' → 3' 

(B) Only template with 5' → 3' polarity is replicated.

(C) Replication is initiated at ori.

(D) DNA polymerase catalyses the process.

(E) The daughter molecule formed has one parental strand.

Choose the correct answer from the options given below:

Concept:

• DNA replication is the process of duplicating the DNA of a cell.
• It takes place in the S-phase of cell cycle.
• Due to replication, each daughter cell formed at the end of the cell cycle has its complete genome.
• DNA has the ability to replicate due to its property of complementary strands.

Important Points

Statement (A) The direction of replication is 5' → 3' - CORRECT

• The enzyme DNA polymerase is responsible for DNA replication.
• It can only add nucleotides to the 3' end of the growing strand, and thus the direction of replication is 5' → 3'.
• During replication, one strand is replicated in the same direction as the unwinding of the helix.
• This strand is called leading strand and replication is continuous in 5' → 3' direction.
• The other strand is the lagging strand on which DNA replication is discontinuous.
• Here, DNA is synthesized in small fragments called Okazaki fragments, and each fragment is also synthesized in the 5' → 3' direction.

Statement (B) Only template with 5' → 3' polarity is replicated - INCORRECT

• During replication, each strand of a double-stranded DNA separates with the help of helicase enzyme.
• Each of these strands act as individual templates for the DNA polymerase to form new complementary DNA strands.
• Thus, the 5' → 3' strand and the 3' → 5' strand will both act as the template DNA and hence get replicated.

Statement (C) Replication is initiated at ori - CORRECT

• Replication can start only at specific sites in the DNA.
• These sites are known as the origin of replication or "ori".

Statement (D) DNA polymerase catalyses the process - CORRECT

• Replication of DNA is carried out by DNA-dependent DNA polymerase enzyme.
• This enzyme is specialized in using DNA as the template and also form another DNA strand by complementarity of bases.

Statement (E) The daughter molecule formed has one parental strand - CORRECT

• Meselson and Stahl showed that the mode of DNA replication in a cell is semi-conservative.
• In this mode of replication, half of the DNA is conserved in the newly formed DNA.
• This means that each daughter DNA molecule will have one parental DNA strand and one newly synthesized DNA strand.

Hence, the correct answer is option 3: (A), (C), (D), (E).