DNA is a naturally occurring polymer found in the nucleus of living cells. Explain how the structure of DNA as a polymer relates to its function in storing genetic information, and describe one key difference between DNA as a natural polymer and a synthetic polymer such as polythene.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
DNA (deoxyribonucleic acid) is a polymer made from monomers called nucleotides. The sequence of these monomers along the DNA chain encodes the instructions needed to build and operate a living organism. Polythene is a synthetic polymer made from ethene monomers and is used to make plastic bags and bottles.
Model answer (5 marks)
DNA is a polymer made from many nucleotides joined by phosphodiester bonds.
1. The order of the nucleotides (A, T, C, G) along the chain encodes genetic information.
2. Different sequences give different genes, so a vast amount of information can be stored.
3. DNA is a natural polymer produced by living cells.
4. Polythene is a synthetic polymer made by humans from a single monomer, ethene.
5. DNA contains four different monomer units, whereas polythene has only one type of repeat unit.
1. The order of the nucleotides (A, T, C, G) along the chain encodes genetic information.
2. Different sequences give different genes, so a vast amount of information can be stored.
3. DNA is a natural polymer produced by living cells.
4. Polythene is a synthetic polymer made by humans from a single monomer, ethene.
5. DNA contains four different monomer units, whereas polythene has only one type of repeat unit.
Examiner tips
- Use the term ‘phosphodiester bond’ to show understanding of the polymer link. Show that the sequence encodes information. Mention the natural vs synthetic origin. Highlight the variety of monomers in DNA vs single monomer in polythene.
Common mistakes
- Confusing the polymer backbone with the bases. Saying DNA is made of ‘monomers’ without naming nucleotides. Failing to note that polythene is synthetic and uses only one monomer.
Mark scheme (5 marks)
- DNA is a polymer made from many monomers (nucleotides) joined together
- The sequence/order of monomers in DNA stores genetic information
- A large number of different monomer sequences are possible, allowing a vast amount of information to be stored
- DNA is a natural polymer (produced by living organisms) whereas polythene is a synthetic polymer (made by humans / in industry)
- DNA has a variety of different monomer units (four different nucleotides), whereas polythene is made from only one type of monomer (ethene/identical repeat units)
Key terms in this question
polymer · natural polymer · synthetic polymer · genetic information
Related
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