Nucleic Acid Structure: DNA & RNA (College Board AP® Biology)

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