Question

The role of DNA ligase in the construction of a recombinant DNA molecule is
A. Formation of phosphodiester bond between two DNA fragments
B. Formation of hydrogen bonds between sticky ends of DNA fragments
C. Ligation of all purine and pyrimidine bases
D. Formation of hydrogen bonds between blunt ends

Answer 1

Hint: DNA ligase is an enzyme that belongs to the ligase class of enzyme classification. The primary function of DNA ligase is to ligate the DNA. DNA ligase can ligate the different types of DNA such as single-stranded DNA, double-stranded DNA, and recombinant DNA molecules.

Step by step answer:There are different types of DNA ligases and each DNA ligase has their action on different DNA molecules. DNA molecule composed of nucleotide units. Each nucleotide unit consists of a ribose sugar, nitrogen base, and phosphate group.
-The four types of nitrogen bases are adenine, guanine, thymine, and cytosine. Out of these four, the adenine and guanine are purines. While the other two are pyrimidines i.e. thymine and cytosine. -Generally, purine pairs with the pyrimidines via hydrogen bonds (Adenine pairs with thymine and guanine pairs with cytosine).
-Nucleotides are attached to form two long strands of DNA which then form a structure called a double helix. Two nucleotides are attached to each other by a phosphodiester bond.
-In recombinant DNA technology, generally, DNA is cleaved with the help of restriction enzymes. Restriction enzymes are the endonucleases that cleave phosphodiester bonds within DNA to form a DNA with a sticky end or blunt end. The restriction enzymes are target specific. Restriction enzymes recognize a specific sequence of nucleotides and produce a double-stranded cut DNA.
-The function of DNA ligase is maintaining DNA integrity by joining breaks in the phosphodiester bonds of DNA that occur during replication and recombination.
Hence, the correct option is option A i.e. Formation of phosphodiester bond between two DNA fragments.

Note: DNA ligases are only capable of forming phosphodiester bonds in order to join two nucleotides. DNA ligases cannot form hydrogen bonds or it can ligate nitrogen bases.