Nucleotides (CIE A Level Biology)

• Nucleic acids such as DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are macromolecules
• Like proteins (polypeptides) and carbohydrates (polysaccharides), these nucleic acids are polymers 
• 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

• 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

Nucleotide Structure Diagram

The basic structure of a nucleotide

Nucleotide Structure Table

Nucleotides in DNA & RNA Diagram

There is much overlap of the nucleotides found in DNA and RNA, the only difference is that RNA contains uracil (U) instead of thymine (T)

ATP

• Adenosine triphosphate (ATP) is the energy-carrying molecule that provides the energy to drive many processes inside living cells
• ATP is another type of nucleotide 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)

ATP Structure Diagram

The structure of AMP, ADP and ATP

• 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
  • This means that they have a double-ring structure
• The bases cytosine, thymine, and uracil are pyrimidines 
  • These bases have a single-ring structure

Purines & Pyrimidines Diagram

The molecular structures of purines and pyrimidines are slightly different