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Chapter 28: Problem 21

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

Short Answer

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Question: Describe the role of hydrophobic interactions in stabilizing double-stranded DNA, lipid bilayers, and soap micelles. Answer: Hydrophobic interactions are non-covalent associations between molecules that are repelled by water. These interactions play a crucial role in stabilizing double-stranded DNA, lipid bilayers, and soap micelles. In double-stranded DNA, hydrophobic interactions occur between adjacent nucleotide bases, minimizing solvent-exposed surface area and stabilizing the double-stranded structure while maintaining the specificity of base pairing. Lipid bilayers are composed of amphipathic molecules with hydrophilic head groups and hydrophobic fatty acid tails. Hydrophobic interactions between the tails stabilize the bilayer arrangement, reducing unfavorable contact between the hydrophobic regions and water. Soap micelles are formed from detergent molecules that consist of a hydrophilic head group and a hydrophobic tail. The formation of micelles is driven by hydrophobic interactions between the tails, stabilizing these structures and allowing them to solubilize and remove dirt and grease from surfaces.

Step by step solution

01

(1. Introduction to hydrophobic interactions)

(Hydrophobic interactions are non-covalent associations between molecules or parts of molecules that are repelled by water. They are driven by the tendency of water molecules to form a clathrate-like cage around hydrophobic molecules, minimizing the contact with water. This water structuring is energetically unfavorable, and it's minimized when hydrophobic molecules/regions are in close proximity, thus promoting their aggregation.)
02

(2a. Hydrophobic interactions in double-stranded DNA)

(In double-stranded DNA, hydrophobic interactions take place primarily between the adjacent nucleotide bases. The stacking of these hydrophobic bases causes the minimization of the solvent-exposed surface area, reducing the entropy loss of water and stabilizing the double-stranded structure. Furthermore, hydrophobic interactions also help to maintain the specificity of base pairing in the DNA strand, which is essential for accurate replication and transcription of genetic information.)
03

(2b. Hydrophobic interactions in lipid bilayers)

(Lipid bilayers are composed of amphipathic molecules with hydrophilic head groups and hydrophobic fatty acid tails. The hydrophilic head groups interact with water, while the hydrophobic tails avoid contact with the aqueous environment. This leads to the formation of a bilayer structure where the heads face the water, and the tails are sequestered towards the center of the bilayer. Hydrophobic interactions between the fatty acid tails stabilize this arrangement, reducing the unfavorable contact between the hydrophobic regions and water.)
04

(2c. Hydrophobic interactions in soap micelles)

(Soap micelles are formed from detergent molecules like sodium stearate. These molecules have a hydrophilic head group (ionic, in this case) and a long hydrophobic tail made from fatty acid chains. When soap is mixed with water, the detergent molecules aggregate to form spherical structures called micelles, where the hydrophobic tails avoid contact with water by clustering in the center, while the hydrophilic heads face the aqueous environment, interacting with water. This micelle formation is driven by hydrophobic interactions between the tails and helps to stabilize these structures, allowing them to solubilize and remove dirt and grease from surfaces.)

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Most popular questions from this chapter

If you read \(\mathrm{J}\). D. Watson's account of the discovery of the structure of DNA, The Double Helix, you will find that for a time in their model-building studies, he and Crick were using alternative (and incorrect, at least in terms of their final model of the double helix) tautomeric structures for some of the heterocyclic bases. (a) Write at least one alternative tautomeric structure for adenine. (b) Would this structure still base-pair with thymine, or would it now base- pair more efficiently with a different base? If so, identify that base.

Draw a structural formula of the DNA tetranucleotide \(5^{\prime}\)-A-G-C-T-3'. Estimate the net charge on this tetranucleotide at \(\mathrm{pH} 7.0\). What is the complementary tetranucleotide to this sequence?

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Glycine, alanine, and valine are classified as nonpolar amino acids. Compare their codons. What similarities do you find? What differences do you find?

The following section of DNA codes for oxytocin, a polypeptide hormone. $$ \text { 3'ACG-ATA-TAA-GTT-TTA-ACG-GGA-GAA-CCA-ACT-5' } $$ (a) Write the base sequence of the mRNA synthesized from this section of DNA. (b) Given the sequence of bases in part (a), write the primary structure of oxytocin.
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