Sticky ends of a fragmented DNA molecule are made of unpaired bases.

Unpaired bases are the correct answer because sticky ends are created through the action of restriction enzymes, specifically endonucleases. Endonucleases are enzymes that cleave DNA at specific recognition sequences, typically palindromic sequences. When these enzymes cleave the DNA molecule, they create fragments with single-stranded overhangs at the ends, which are called sticky ends.

Endonucleases cleave the DNA molecule at specific recognition sequences, creating fragments with single-stranded overhangs at the ends.

Endonucleases recognize specific DNA sequences and cleave the phosphodiester bonds within the DNA molecule. These enzymes can cleave DNA in a staggered manner, resulting in fragments with single-stranded overhangs. The overhangs are composed of unpaired bases, which are not complementary to any bases on the opposite strand.

The unpaired bases in sticky ends allow for the formation of hydrogen bonds with complementary sequences.

Because the overhangs in sticky ends are unpaired, they can form temporary bonds with complementary sequences. These temporary bonds are formed through hydrogen bonding between the unpaired bases. The specificity of base pairing ensures that the sticky ends can only bind to their complementary sequences, allowing for the targeted manipulation of DNA fragments.

Sticky ends are commonly used in molecular biology techniques such as DNA cloning and recombinant DNA technology.

The ability of sticky ends to form temporary bonds with complementary sequences is crucial in many molecular biology techniques. For example, in DNA cloning, sticky ends can be used to join DNA fragments from different sources. The sticky ends of the DNA fragments are first treated with a DNA ligase enzyme, which catalyzes the formation of phosphodiester bonds between the fragments. This results in the creation of a recombinant DNA molecule.

Conclusion:
In summary, the sticky ends of a fragmented DNA molecule are made of unpaired bases. These unpaired bases allow for the formation of temporary hydrogen bonds with complementary sequences, which is essential for various molecular biology techniques.