Explain why DNA is described as a polymer made up of monomers, and state what the monomers of DNA are called.

WJEC GCSE Biology (Wales) — 2.3.1 DNA structure · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

DNA carries the genetic information needed to build and run every living organism. Scientists classify DNA as a biological polymer.

Model answer (4 marks)

A polymer is a large molecule made up of many repeated smaller units (monomers) joined together.
DNA is a polymer because it is made of many monomers joined in a long chain.
The monomers of DNA are called nucleotides.
Each nucleotide contains a sugar (deoxyribose), a phosphate group, and one of four bases.

Examiner tips

Use the definition of a polymer first, then state DNA is a polymer, then name the monomers and describe their components.
Show the four bases (A, T, C, G) if space allows to demonstrate depth of knowledge.

Common mistakes

Confusing nucleotides with nucleic acids, or saying ‘DNA is a polymer of bases’ instead of nucleotides.
Omitting the sugar and phosphate groups in the description of a nucleotide.

Mark scheme (4 marks)

A polymer is a large molecule made up of many repeated smaller units (monomers) joined together
DNA is a polymer because it is made of many monomers joined in a long chain
The monomers of DNA are called nucleotides
Each nucleotide contains a sugar (deoxyribose), a phosphate group, and one of four bases

Key terms in this question

polymer · monomer