3.1.5.1 Structure of DNA and RNA

Okay so we need to know alllll about DNA and RNA. To start, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are important information-carrying molecules. In all living cells, DNA holds genetic information and RNA transfers genetic information from DNA to the ribosomes. Ribosomes are formed from RNA and proteins. Both DNA and RNA are polymers of nucleotides. Each nucleotide is formed from a pentose, a nitrogen-containing organic base and a phosphate group. That was a nice little summary.


The components of a DNA nucleotide are:

•  deoxyribose
• a phosphate group
• one of the organic bases:
•  adenine
• cytosine
• guanine
• thymine

The components of an RNA nucleotide are:

• ribose
• a phosphate group
• one of the organic bases:
• adenine
• cytosine
• guanine
• uracil

A condensation reaction between two nucleotides forms a phosphodiester bond. A DNA molecule is a double helix with two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs. In DNA, adenine binds to thymine and guanine binds to cytosine. It follows that a DNA molecule will have the same percentage of adenine/thymine, and the same percentage of cytosine/guanine.

An RNA molecule is a relatively short polynucleotide chain. It is also single stranded.