Structure and Roles of Nucleic Acids
FIGURE 1: Structure of DNA
Pyrimidines- Pyrimidine is one of two classes of heterocyclic nitrogenous bases found in the
nucleic acids DNA and RNA: in DNA the pyrimidines are cytosine and thymine, in RNA uracil
replaces thymine. Always have a single ring structure.
Purines- have a double ring structure and larger than pyrimidines. A purine always pair with a
pyrimidine. A-T and C-G in DNA and A-U and C-G when RNA is involved.
Structure of purines and pyrimidines
Nature of hydrogen bonds- The hydrogen bonding in the DNA bases of one purine (guanine and
adenine) and one pyrimidine (cytosine and thymine) creates a similar shape. Cytosine and Guanine
are held together by three hydrogen bonds. The pairing of adenine and thymine share two hydrogen
bonds, thus the bond is slightly weaker and slightly longer.
FUGURE 1V: Structure of DNA and RNA.
Table showing comparison between DNA and RNA.
DNA
Double stranded
Deoxyribose sugar
Uses thymine
Can last for a long time
Can self-replicate
Stores genetic information
Is read 3’>5’
RNA
Single stranded
Ribose sugar
Uses uracil
Does not usually last for a long time
Can have multiple structures (mRNA, rRNA,
tRNA)
Stores information about protein structure
Is formed in 5’>3’
References:
1) Jones ME (1980). “Pyrimidine nucleotide biosynthesis in animals: genes, enzymes, and
regulation of UMP biosynthesis”. Annual Review of Biochemistry. 49 (1): 253–79.
2) McMurry JE, Begley TP (2005). The organic chemistry of biological pathways. Roberts &
Company.