DNA and Naturally Occurring Polymers
Get to grips with DNA and Naturally Occurring Polymers for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) chemistry topic: DNA is a natural condensation polymer of two strands, alongside starch, cellulose and proteins.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Many naturally occurring polymers are formed by condensation polymerisation, and DNA is the most important example. This is a Triple-only topic.
DNA — deoxyribonucleic acid — encodes genetic instructions for the development and functioning of living organisms. Most DNA molecules consist of two polymer chains made from four different monomers called nucleotides, and these two chains are wound together in the form of a double helix.
Other naturally occurring polymers include starch and cellulose, which are both made from sugars, and proteins, which are made from amino acids. All are condensation polymers, formed with the release of water.
Revision notes
DNA structure
DNA encodes the genetic instructions for the development and functioning of living organisms.
Most DNA molecules consist of two polymer chains made from four different monomers called nucleotides. The two chains are wound together in the form of a double helix.
Other natural polymers
Starch and cellulose are both polymers made from sugars — specifically from glucose monomers.
Proteins are polymers made from amino acids. All of these, like DNA, are formed by condensation polymerisation.
Why condensation
In each case a small molecule, usually water, is released as the monomers join.
This is what makes them condensation polymers rather than addition polymers, and it links this topic directly to amino acids and proteins.
Key points
- DNA is a naturally occurring condensation polymer.
- DNA encodes genetic instructions.
- DNA is made from four different nucleotides.
- Two DNA chains form a double helix.
- Starch and cellulose are polymers of sugars.
- Proteins are polymers of amino acids.
Worked examples
Example 1
Name the monomers from which DNA is made and state how many different types there are. [2 marks]
Model answer
Nucleotides (1 mark), of which there are four different types (1 mark).
Example 2
Describe the overall structure of a DNA molecule. [2 marks]
Model answer
It consists of two polymer chains (1 mark) wound together in the form of a double helix (1 mark).
Example 3
Name two naturally occurring polymers other than DNA and state what each is made from. [4 marks]
Model answer
Starch is a polymer made from sugars (2 marks). Proteins are polymers made from amino acids (2 marks).
Common mistakes
Saying DNA is an addition polymer.
It is a condensation polymer, formed with the release of water.
Naming the monomers as amino acids.
DNA monomers are nucleotides; amino acids form proteins.
Saying DNA has one chain.
Most DNA molecules have two chains wound into a double helix.
Forgetting there are four different nucleotides.
The number is examinable.
Exam tips
- Learn nucleotides as the DNA monomer and that there are four types.
- Say double helix when describing the structure.
- Group starch, cellulose, proteins and DNA as natural condensation polymers.
- Remember this is a Triple-only topic.
Key terms
- DNA
- Deoxyribonucleic acid, a natural condensation polymer.
- Nucleotide
- The monomer from which DNA is made.
- Double helix
- The twisted two-chain structure of DNA.
- Cellulose
- A natural polymer made from sugars.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.