Comparing DNA & RNA Structure
DNA
- DNA is a polynucleotide – it is made up of many nucleotides linked together in a chain
- Sugar-phosphate bonds in DNA (between different nucleotides in the same strand) are strong covalent bonds
- The nitrogenous bases in DNA stick out sideways from the sugar-phosphate backbone
- DNA nucleotides contain the nitrogenous bases adenine (A), guanine (G), thymine (T) and cytosine (C)
- DNA nucleotides contain the pentose sugar deoxyribose
- DNA molecules are made up of 2 polynucleotide strands (they are double-stranded)
- DNA polynucleotide chains are very long
RNA
- RNA is also a polynucleotide – it is made up of many nucleotides linked together in a chain
- RNA nucleotides also contain the nitrogenous bases adenine (A), guanine (G), and cytosine (C)
- Sugar-phosphate bonds in RNA are strong covalent bonds as they are in DNA
- The nitrogenous bases in RNA stick out sideways from the sugar-phosphate backbone, the same way they do in DNA
- Unlike DNA, RNA nucleotides never contain the nitrogenous base thymine (T) – in place of this they contain the nitrogenous base uracil (U)
- Unlike DNA, RNA nucleotides contain the pentose sugar ribose (instead of deoxyribose)
- Unlike DNA, RNA molecules are only made up of 1 polynucleotide strand (they are single stranded)
- Unlike DNA, RNA polynucleotide chains are relatively short compared to DNA
Diagram comparing DNA and RNA Nucleotide Structures
An RNA nucleotide (above) compared with a DNA nucleotide (below)
Nucleotide Structure Summary Table
| Properties | DNA | RNA |
| Pentose sugar | Deoxyribose | Ribose |
| Bases |
Adenine (A) |
Adenine (A) Uracil (U) Cytosine (C) Guanine (G) |
| Number of strands | Double stranded (double helix) | Single stranded |
Exam Tip
You need to know the difference between DNA and RNA molecules (base composition, number of strands, pentose sugar present).
A common error is to describe DNA or RNA as polymers of bases; more correctly, they are polymers of nucleotides
