- Nucleic acids such as DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are macromolecules (giant molecules)
- Like proteins (polypeptides) and carbohydrates (polysaccharides), these nucleic acids are polymers (‘poly’ meaning ‘many’)
- This means they are made up of many similar, smaller molecules (known as subunits or monomers) joined into a long chain
- The subunits that make up DNA and RNA are known as nucleotides
- Therefore DNA and RNA can also be known as polynucleotides
- Nucleotides are made up of three components:
- A nitrogen-containing base (also known as a nitrogenous base)
- A pentose sugar (containing 5 carbon atoms)
- A phosphate group
- Adenosine triphosphate (ATP) is the energy-carrying molecule that provides the energy to drive many processes inside living cells
- ATP is another type of nucleic acid and hence it is structurally very similar to the nucleotides that make up DNA and RNA
- It is a phosphorylated nucleotide
- Adenosine (a nucleoside) can be combined with one, two or three phosphate groups
- One phosphate group = adenosine monophosphate (AMP)
- Two phosphate groups = adenosine diphosphate (ADP)
- Three phosphate groups = adenosine triphosphate (ATP)
Don’t worry – you are not expected to know the structural formulae for the nucleotides that make up DNA and RNA or AMP, ADP and ATP (as in the diagram above)! You just need to learn the different groups that they are made up of (phosphate groups, pentose sugars and nitrogenous bases).
Remember that adenine is a nitrogenous base whereas adenosine is a nucleoside (a base – adenine, attached to a pentose sugar).
- The nitrogenous base molecules that are found in the nucleotides of DNA (A, T, C, G) and RNA (A, U, C, G) occur in two structural forms: purines and pyrimidines
- The bases adenine and guanine are purines – they have a double ring structure
- The bases cytosine, thymine and uracil are pyrimidines – they have a single ring structure
You don’t need to know the structural formulae of these bases, just which are purines and which are pyrimidines.