AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
The DNA polymer is made up of repeating nucleotide units.
Full specification wording
DNA structure (biology only): The DNA polymer is made up of repeating nucleotide units.
DNA is a polymer built from many repeating monomer units called nucleotides.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 7 of 19
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
DNA is a polymer built from many repeating monomer units called nucleotides. Each nucleotide has three parts: a phosphate group, a deoxyribose sugar and one of four bases (A, T, C or G). Nucleotides join together in a condensation reaction between the phosphate of one nucleotide and the sugar of the next, forming a sugar-phosphate backbone. The base attached to each sugar can vary, so the sequence of bases along the polymer stores genetic information. For example, a single DNA strand can be represented as a chain of nucleotides, each contributing a sugar, a phosphate and a base. The two strands of a DNA molecule are held together by hydrogen bonds between complementary bases, forming the double helix.
What earns the marks
- DNA is a polymer made of repeating monomer units called nucleotides.
- Each nucleotide consists of a phosphate group, a deoxyribose sugar and a base.
- Nucleotides join by condensation reactions between the phosphate of one nucleotide and the sugar of the next.
- The sugar-phosphate backbone is formed by the alternating sugar and phosphate components of adjacent nucleotides.
- The four bases (A, T, C, G) can be in any order along the strand, and their sequence carries genetic information.
Common mistakes and how to put them right
Thinking that a nucleotide contains only a base.
Put it right: A nucleotide also contains a phosphate group and a deoxyribose sugar.
Confusing nucleotides with amino acids.
Put it right: Nucleotides are the monomers of DNA, while amino acids are the monomers of proteins.
Believing that all nucleotides in DNA are identical.
Put it right: They share the same sugar and phosphate but can have different bases.
Exam tips
- When describing DNA as a polymer, always name the monomer as a nucleotide and list its three components.
- Use the term condensation reaction to explain how nucleotides join and water is released.
- Link the repeating nucleotide structure to the sugar-phosphate backbone and the base sequence.
Try the lesson
The start of the DNA structure (biology only): The DNA polymer is made up of repeating nucleotide units. lesson, made from checked teaching notes for this specification point.
Have a go first
The DNA polymer is made up of many repeating units. What is the name of each repeating unit?
Listen
DNA is a polymer built from many repeating monomer units called nucleotides. Each nucleotide has three parts: a phosphate group, a deoxyribose sugar and one of four bases (A, T, C or G). Nucleotides join together in a condensation reaction between the phosphate of one nucleotide and the sugar of the next, forming a sugar-phosphate backbone. The base attached to each sugar can vary, so the sequence of bases along the polymer stores genetic information. For example, a single DNA strand can be represented as a chain of nucleotides, each contributing a sugar, a phosphate and a base. The two strands of a DNA molecule are held together by hydrogen bonds between complementary bases, forming the double helix. A strong answer earns marks for these points. DNA is a polymer made of repeating monomer units called nucleotides. Each nucleotide consists of a phosphate group, a deoxyribose sugar and a base. Nucleotides join by condensation reactions between the phosphate of one nucleotide and the sugar of the next. The sugar-phosphate backbone is formed by the alternating sugar and phosphate components of adjacent nucleotides. Exam tip: When describing DNA as a polymer, always name the monomer as a nucleotide and list its three components.
See it
Key words
Say what each word means before you turn the card.
Nucleotide
Try answering aloud or in your head before turning the card.
Condensation reaction
Try answering aloud or in your head before turning the card.
Sugar-phosphate backbone
Try answering aloud or in your head before turning the card.
Base sequence
Try answering aloud or in your head before turning the card.
See every definition
- Nucleotide
- A repeating monomer unit of the DNA polymer, made up of a phosphate group, a deoxyribose sugar and one of four bases.
- Condensation reaction
- The reaction in which nucleotides join together between the phosphate of one nucleotide and the sugar of the next.
- Sugar-phosphate backbone
- The structure formed by the alternating sugar and phosphate components of adjacent nucleotides joined together.
- Base sequence
- The order of the four bases along the strand, which stores genetic information.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of DNA structure (biology only): The DNA polymer is made up of repeating nucleotide units.
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge