The genetic code is based on four different bases with the structures shown here. Assign a geometry and hybridization to each interior atom in these four bases.
The correct answer and explanation is:
The four nitrogenous bases in the genetic code are adenine (A), thymine (T), cytosine (C), and guanine (G). Each of these bases contains various atoms, primarily carbon, nitrogen, hydrogen, and oxygen. The geometry and hybridization of each atom in these bases depend on its bonding and atomic structure. Let’s break down the hybridization and geometry for each atom involved.
Adenine (A)
Adenine is a purine base with a fused double-ring structure.
- Carbon atoms in adenine are sp² hybridized. These carbon atoms form a planar ring structure with 120° bond angles.
- Nitrogen atoms are also sp² hybridized. They participate in the aromatic π-system, contributing to the base’s planar geometry.
- Hydrogen atoms attached to carbon or nitrogen atoms follow the sp² hybridization.
Thymine (T)
Thymine is a pyrimidine base with a six-membered ring.
- Carbon atoms in thymine are sp² hybridized. Each carbon atom forms bonds with other atoms in the planar structure of the pyrimidine ring.
- Nitrogen atoms are sp² hybridized. The nitrogen atoms in the ring structure also participate in the delocalized π-system, contributing to its planarity.
- Oxygen atoms in thymine are sp² hybridized, attached to the carbons through double bonds, and each oxygen atom has a trigonal planar geometry.
Cytosine (C)
Cytosine is also a pyrimidine base similar to thymine but with an amino group attached to the ring.
- Carbon atoms are sp² hybridized, forming a planar ring.
- Nitrogen atoms in cytosine are sp² hybridized. The nitrogen and the attached amino group provide additional electron density to the structure.
- Oxygen atoms are sp² hybridized, as they are double-bonded to carbon.
Guanine (G)
Guanine is a purine base, like adenine, with a double-ring structure.
- Carbon atoms are sp² hybridized, forming part of the planar structure.
- Nitrogen atoms are sp² hybridized, forming part of the aromatic π-system.
- Oxygen atoms in guanine are sp² hybridized. These oxygen atoms form double bonds with carbon, and their bond angles are approximately 120°.
Conclusion:
In all four bases, the interior atoms (carbon, nitrogen, and oxygen) typically adopt sp² hybridization due to the planar and conjugated nature of the aromatic rings. This allows the nitrogenous bases to interact with each other, facilitating base pairing in the double helix structure of DNA.