Question

Discuss the role of the hydrophobic interactions in stabilizing the following. (a) Double-stranded DNA (b) Lipid bilayers (c) Soap micelles

Short answer

Answer: Hydrophobic interactions play a crucial role in stabilizing various biological structures, including double-stranded DNA, lipid bilayers, and soap micelles. In double-stranded DNA, hydrophobic interactions orient the hydrophobic nucleotide bases towards the interior of the helix, away from the polar environment, increasing the DNA's stability. In lipid bilayers, hydrophobic interactions cause the phospholipids' hydrophobic tails to form the bilayer's interior, while the hydrophilic heads face the exterior, providing stability to the structure. Lastly, in soap micelles, hydrophobic interactions lead to the clustering of hydrophobic tails at the core of the micelle, while hydrophilic heads form the outer shell, contributing to the micelle's stability.

Step-by-step solution

1. Introduction to Hydrophobic Interactions

Hydrophobic interactions are non-covalent interactions between nonpolar molecules in an aqueous or polar environment. The interaction arises from the tendency of water molecules to form an energetically favorable hydrogen-bonding network around the nonpolar molecules, ultimately resulting in the clustering or exclusion of these nonpolar molecules from the polar environment. This phenomenon occurs because water molecules favor interactions with other polar molecules (hydrophilic) than with nonpolar (hydrophobic) ones.

2. Double-stranded DNA

Double-stranded DNA (dsDNA) is a molecular structure composed of two complementary strands of deoxyribonucleic acid. The two strands are held together by hydrogen bonds between specific base pairs - adenine (A) with thymine (T) and cytosine (C) with guanine (G). Additionally, the sugar-phosphate backbone forms the outer structure of the DNA double helix, with the nucleotide bases pointing toward the center of the helix. The backbone is composed of polar groups, making it hydrophilic, while the nucleotide bases are hydrophobic.

3. Role of Hydrophobic Interactions in Stabilizing dsDNA

In the case of dsDNA, hydrophobic interactions contribute to the stabilization of the double helix by orienting the hydrophobic nucleotide bases toward the interior of the helix and away from the surrounding polar environment (mainly water). This arrangement minimizes the unfavorable interactions between the hydrophobic bases and water, gives rise to base stacking interactions, and exposes the polar sugar-phosphate backbone to the aqueous environment. These factors collectively increase the stability of the dsDNA structure.

4. Lipid Bilayers

Lipid bilayers are the basic structural components of biological membranes, such as the cell membrane. They consist of two opposing layers of lipids, mainly phospholipids, which have a polar hydrophilic head and two nonpolar hydrophobic tails.

5. Role of Hydrophobic Interactions in Stabilizing Lipid Bilayers

The stabilization of lipid bilayers relies heavily on hydrophobic interactions. In an aqueous environment, the hydrophobic tails of the phospholipids tend to avoid contact with water, while the hydrophilic heads interact with the surrounding water molecules. This arrangement drives the formation of a bilayer, in which the hydrophobic tails form the interior, and the hydrophilic heads face the exterior. The hydrophobic interactions among the tails contribute significantly to the overall stability of the lipid bilayer.

6. Soap Micelles

Soap micelles are spherical aggregates formed by soap molecules (amphiphiles) when dissolved in water. Soap molecules typically have a polar hydrophilic head and a nonpolar hydrophobic tail.

7. Role of Hydrophobic Interactions in Stabilizing Soap Micelles

When soap molecules are dispersed in an aqueous environment, their hydrophobic tails tend to escape from the polar surroundings, while their hydrophilic heads interact with water. This tendency leads to the formation of micelles, in which hydrophobic tails cluster together at the core, and hydrophilic heads face the water, forming the outer shell. Thus, hydrophobic interactions among the nonpolar tails play a pivotal role in the stability and formation of soap micelles.