CIE A Level Biology复习笔记6.1.1 Nucleotides

• 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

• 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

The basic structure of a nucleotide

Nucleotide structure table

The nucleotides found in DNA and RNA

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 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)

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 – they have a double ring structure
• The bases cytosine, thymine and uracil are pyrimidines – they have a single ring structure

The molecular structures of purines and pyrimidines are slightly different