Learning Objective: Describe the structural components of nucleic acids—including pentose sugars, nitrogenous bases, nucleosides, and nucleotides—and distinguish between purines, pyrimidines, and the differences between DNA and RNA.
Nucleic Acids and Their Components
Nucleic acids (DNA and RNA) are polymers assembled from nucleotides, each containing:
- A nitrogenous base
- A five-carbon sugar (pentose)
- One or more phosphate groups
Activity
Five-Carbon Sugars
The pentose determines the type of nucleic acid:
- Ribose → RNA
- Deoxyribose → DNA
Deoxyribose lacks an oxygen at the 2′ carbon, making DNA more stable.
Nitrogenous Bases
Nitrogenous bases are of two types:
Purines (Two Rings)
- Adenine (A)
- Guanine (G) (found in both DNA and RNA)
Other purine metabolites (not in nucleic acids): xanthine, hypoxanthine, uric acid
Pyrimidines (One Ring)
- Cytosine (C): DNA & RNA
- Thymine (T): DNA only
- Uracil (U): RNA only
Activity
Nucleosides and Nucleotides
Nucleosides
Base + sugar (bonded at the 1′ carbon)
Nucleotides
Nucleoside + phosphate(s) at the 5′ carbon
- Mono-, di-, or triphosphates
- Di- and triphosphates (e.g., ATP) contain high-energy phosphate bonds
Common Examples
- UMP – uridine monophosphate
- ATP – adenosine triphosphate
- dGMP – deoxyguanosine monophosphate
“Deoxy-” is often omitted for thymine derivatives because they naturally occur with deoxyribose.
