Question

Name three intermolecular forces that stabilize the structure of DNA, and explain how they act.

Short answer

The three forces are hydrogen bonds, Van der Waals forces, and ionic interactions. They act by forming base pairs, stabilizing stacked bases, and balancing charge respectively.

Step-by-step solution

Identify the three intermolecular forces

DNA is stabilized by multiple intermolecular forces. The three primary ones are hydrogen bonds, Van der Waals forces, and ionic interactions.

Explain Hydrogen Bonds

Hydrogen bonds occur between complementary bases (adenine and thymine, guanine and cytosine). These bonds are crucial for the base pairing that holds the two DNA strands together.

Explain Van der Waals Forces

Van der Waals forces, or London dispersion forces, act between the stacked bases in the DNA double helix. These weak forces help stabilize the stacked structure of the DNA.

Explain Ionic Interactions

Ionic interactions involve the negatively charged phosphate groups along the DNA backbone and positively charged ions in the surrounding solution (e.g., magnesium ions). These interactions help maintain the structural integrity of the DNA molecule.

Key concepts

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Intermolecular forces play a crucial role in maintaining the structure and stability of DNA. DNA's intricate double helix form is stabilized by three main types of intermolecular forces: hydrogen bonds, Van der Waals forces, and ionic interactions. Let's dive deeper into each of these forces to understand how they contribute to DNA's stability.

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Hydrogen bonds are a key player in holding the DNA double helix together. They form between specific pairs of nitrogenous bases:

• Adenine (A) pairs with Thymine (T)
• Guanine (G) pairs with Cytosine (C)

For example, two hydrogen bonds exist between adenine and thymine, while three hydrogen bonds link guanine and cytosine.
These bonds are relatively weak compared to covalent bonds, but because there are so many of them in a DNA molecule, they collectively create a strong stabilizing force. This ensures that the two strands of DNA remain tightly aligned through complementary base pairing.

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Van der Waals forces (also known as London dispersion forces) contribute to the stability of DNA by acting between the stacked bases in the DNA double helix. While these forces are very weak individually, they play a significant role in the overall stability due to the number of interactions along the entire length of the DNA molecule.
Because of the stacking effect, the aromatic rings of the bases are precisely spaced in parallel orientation, which maximizes the overlap of electron clouds. This overlap creates a slight attraction between the bases, helping to stabilize the helical structure.

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Ionic interactions are essential for maintaining the integrity of the DNA structure. The DNA backbone consists of a series of negatively charged phosphate groups. These negative charges could repel each other and destabilize the molecule if not for the presence of positively charged ions in the surrounding cellular environment.

• Common positive ions include magnesium (Mg²⁺), sodium (Na⁺), and potassium (K⁺).

These cations neutralize the negative charges on the phosphate groups, reducing repulsion and helping to hold the DNA structure together. This balance of charges ensures that the DNA molecule remains intact and properly functioning within the cell.