How are the group of adjacent nucleotides joined?

Phosphodiester bond

The correct answer is option 4. Phosphodiester bond.

In nucleic acids like DNA and RNA, nucleotides are the building blocks that form long chains. These nucleotides consist of three main components: a phosphate group, a sugar molecule (deoxyribose in DNA and ribose in RNA), and a nitrogenous base (adenine, guanine, cytosine, thymine in DNA, and uracil in RNA).

Adjacent nucleotides in a nucleic acid chain are joined by what is called a phosphodiester bond. Here's how it forms:

Phosphate Group: Each nucleotide has a phosphate group attached to the 5' carbon of its sugar molecule. This phosphate group is negatively charged due to the presence of oxygen atoms with extra electrons.

Sugar Molecule: The sugar molecule of each nucleotide contains a hydroxyl group (-OH) attached to its 3' carbon.

Bond Formation: When two nucleotides come together, the phosphate group of one nucleotide reacts with the hydroxyl group of the adjacent nucleotide. During this reaction, a molecule of water (H₂O) is released, and a covalent bond forms between the phosphate group's oxygen and the sugar molecule's carbon.

Specifically, the phosphate group's oxygen (O) binds to the 3' carbon of one sugar molecule, while the phosphate group's phosphate (P) binds to the 5' carbon of the next sugar molecule, forming a linkage between the two sugars. This creates what is known as a phosphodiester bond.

Repeat: This process repeats as additional nucleotides are added to the growing nucleic acid chain, forming a long linear polymer with a backbone made of alternating sugar and phosphate groups.

The phosphodiester bond plays a crucial role in maintaining the integrity and stability of the nucleic acid chain. It provides strength to the backbone while still allowing flexibility for the molecule to adopt different conformations as needed for various biological functions, such as DNA replication, transcription, and translation.

In summary, phosphodiester bonds join adjacent nucleotides in nucleic acids by linking the phosphate group of one nucleotide to the sugar molecule of the next nucleotide, forming a backbone structure essential for storing and transmitting genetic information.