Chapter 18: Problem 61

Below are shown the hydrogen bonds that form between the \(C-G\) and \(A-T\) pairs of bases. What type of functional groups are involved in hydrogen bonding? Why does the A-T pair form only two hydrogen bonds and not three?

Short Answer

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The functional groups involved in hydrogen bonding between DNA base pairs are amino groups, carbonyl groups, and imino groups. In C-G base pairs, three hydrogen bonds are formed because they have ample functional groups to donate and accept hydrogen atoms. However, A-T base pairs form only two hydrogen bonds due to the limited availability of functional groups capable of participating in hydrogen bonding.

Step by step solution

Identifying DNA base pairs and hydrogen bonding

In DNA, there are four bases: adenine (A), guanine (G), cytosine (C), and thymine (T). These bases pair with each other to form the structure of the DNA double helix, with A pairing with T and G pairing with C. The nitrogenous bases interact through hydrogen bonds, which stabilize the DNA structure.

Identifying functional groups in DNA base pairs

The nitrogenous bases involved in hydrogen bonding contain specific functional groups that can donate or accept hydrogen atoms. Generally, the functional groups involved in hydrogen bonding in these base pairs include amino groups, carbonyl groups, and imino groups. The amino groups (-NH2) can serve as hydrogen bond donors, while the carbonyl groups (C=O) and imino groups (=N-) can serve as hydrogen bond acceptors.

Describing hydrogen bonding in C-G pairs

In a C-G base pair, there are three hydrogen bonds formed. The cytosine contains an amino group that can donate a hydrogen bond to the oxygen of the guanine's carbonyl group. Similarly, one of the nitrogen atoms in the cytosine's imino group can donate a hydrogen bond to the amino group of the guanine. Lastly, another nitrogen atom in the guanine's imino group donates a hydrogen bond to the oxygen of the carbonyl group of cytosine.

Describing hydrogen bonding in A-T pairs

In an A-T base pair, there are only two hydrogen bonds formed. The adenine contains an amino group that can donate a hydrogen atom to the oxygen in the thymine's carbonyl group. The thymine also has an amino group that donates a hydrogen atom to the nitrogen in the adenine's imino group. There are no additional functional groups capable of donating or accepting hydrogen atoms in the A-T base pair, which is why only two hydrogen bonds are formed.

Summary

The functional groups involved in hydrogen bonding between the DNA base pairs are amino groups, carbonyl groups, and imino groups. The C-G base pair forms three hydrogen bonds, while the A-T base pair forms only two hydrogen bonds due to the limited availability of functional groups capable of participating in hydrogen bonding.

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Below are shown the hydrogen bonds that form between the \(C-G\) and \(A-T\) pairs of bases. What type of functional groups are involved in hydrogen bonding? Why does the A-T pair form only two hydrogen bonds and not three?

Short Answer

Step by step solution

Identifying DNA base pairs and hydrogen bonding

Identifying functional groups in DNA base pairs

Describing hydrogen bonding in C-G pairs

Describing hydrogen bonding in A-T pairs

Summary

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