Bond Strength in DNA

[Aishwarya Kosgi 1F]

Hi! I had a question about AT and GC pairs in DNA. Since AT base pairs have only 2 hydrogen-bonding sites and GC has 3 hydrogen bonding sites, is GC stronger? Or are the bond strengths of AT and GC pretty comparable because they both are able to hydrogen bond? I was wondering if that 3rd h-bond in GC makes a big difference? Thank you!

[Victor Li 2A]

You are correct that G-C DNA bond pairs are stronger since they have 3 hydrogen bonds. This is also why DNA strands that are rich in G-C base pairs require higher temperatures to be denatured.

[Kristina Krivenko 3I]

I'm not sure by how much but G-C pair is definitely stronger since, as you mentioned, G-C pair can form 3 hydrogen bonds whereas A-T pair can form only 2. In his lectures, Dr. Lavelle mentioned that the effect of IMFs adds up, and, thus, G-C pairs are more stable.

[Navdha Sharma 3J]

G-C bonds are stronger as they are triple bonds while A-T bonds are only double bonds. Due to larger bond strength, G-C bonds are more stable too.

[AnjikaFriedman-Jha2D]

The ability to form 3 hydrogen bonds compared to 2 bonds would make G-C base pairs both stronger and more stable

[Tobie Jessup 2E]

The strength of intermolecular interactions increase with the number of individual interactions/bonds, so the 3 hydrogen bonds in G-C bonding makes them strong than A-T bonding which only has 2 hydrogen bonds.

[Gustavo_Chavez_1K]

Yeah so since the G-C pair has 3 hydrogen bonds in comparison to A-T which only has 3, G-C pairs would be considered both stronger and more stable. Also, this would explain why G-C pair bonds need higher temperatures to be denatured.

[Joey_Okumura_1E]

Recall that for intramolecular forces, multiple bonds are stronger than single bonds. The same concept applies to intermolecular bonds. The strength and quantity are directly related.

[Yuehan_Wu_3K]

GC bonds are much stronger because they have three hydrogen bonds connected while AT bonds only have two linked hydrogen bonds.

[Melanie Lin 3E]

That's correct! With more hydrogen bonds, GC pairs are markedly stronger than AT pairs. So DNA with low GC ratio often times are less stable compared to DNA with high GC ratio!

[Arnav Saud 2C]

GC is stronger than AT because it has one extra h bond.

[vanessanguyen3I]

GC is stronger because it has an extra hydrogen bond. This means that more heat is needed to break the bonds between GC versus the bonds between AT.

[Gabriel Nitro 1E]

Hi,

Yes! That is correct! The additional hydrogen bond makes the GC attractions stronger!

Hope this helps! :)