AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Each nucleotide consists of a common sugar and phosphate group with one of…
Full specification wording
DNA structure (biology only): Each nucleotide consists of a common sugar and phosphate group with one of four different bases attached to the sugar.
A nucleotide is the building block of DNA.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 2 of 19
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A nucleotide is the building block of DNA. Every nucleotide has the same two parts: a sugar molecule called deoxyribose and a phosphate group. Attached to the sugar is one base, and there are four possible bases: adenine (A), cytosine (C), guanine (G) and thymine (T). Because the sugar and phosphate are common to all nucleotides, the four nucleotides differ only in which base is attached. In a DNA strand, the sugar of one nucleotide bonds to the phosphate of the next, forming a repeating sugar-phosphate backbone. The bases project from this backbone and pair with bases on the opposite strand. When describing a nucleotide, always include all three parts: sugar, phosphate and base.
What earns the marks
- A nucleotide contains a sugar called deoxyribose.
- A nucleotide contains a phosphate group.
- The sugar and phosphate are common to all nucleotides.
- One of four different bases is attached to the sugar.
- The four bases are adenine, cytosine, guanine and thymine.
- Nucleotides differ from each other only in the base they contain.
Common mistakes and how to put them right
Saying the base is attached to the phosphate.
Put it right: The base is attached to the sugar.
Listing only two components of a nucleotide.
Put it right: A nucleotide has a sugar, a phosphate group and a base.
Believing each nucleotide has a different sugar.
Put it right: The sugar is common to all four nucleotides.
Exam tips
- Draw or describe a nucleotide with the base attached to the sugar, not the phosphate.
- Name the sugar as deoxyribose to show precise knowledge.
- Use the phrase 'common sugar and phosphate group' when contrasting the four nucleotides.
Try the lesson
The start of the DNA structure (biology only): Each nucleotide consists of a common sugar and phosphate group with one of four different bases attached to the sugar. lesson, made from checked teaching notes for this specification point.
Have a go first
In a DNA nucleotide, which part is attached to the sugar and can be one of four different types?
Listen
A nucleotide is the building block of DNA. Every nucleotide has the same two parts: a sugar molecule called deoxyribose and a phosphate group. Attached to the sugar is one base, and there are four possible bases: adenine (A), cytosine (C), guanine (G) and thymine (T). Because the sugar and phosphate are common to all nucleotides, the four nucleotides differ only in which base is attached. In a DNA strand, the sugar of one nucleotide bonds to the phosphate of the next, forming a repeating sugar-phosphate backbone. The bases project from this backbone and pair with bases on the opposite strand. When describing a nucleotide, always include all three parts: sugar, phosphate and base. A strong answer earns marks for these points. A nucleotide contains a sugar called deoxyribose. A nucleotide contains a phosphate group. The sugar and phosphate are common to all nucleotides. One of four different bases is attached to the sugar. A common slip: Saying the base is attached to the phosphate. Instead, the base is attached to the sugar. Exam tip: Draw or describe a nucleotide with the base attached to the sugar, not the phosphate.
See it
Key words
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Nucleotide components
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Common sugar and phosphate
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Four bases attached to sugar
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Sugar-phosphate backbone
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See every definition
- Nucleotide components
- Each nucleotide consists of a common sugar and phosphate group with one of four different bases attached to the sugar.
- Common sugar and phosphate
- The sugar and phosphate are common to all nucleotides, so the four nucleotides differ only in which base is attached.
- Four bases attached to sugar
- Attached to the sugar is one base, and there are four possible bases: adenine, cytosine, guanine and thymine.
- Sugar-phosphate backbone
- In a DNA strand, the sugar of one nucleotide bonds to the phosphate of the next, forming a repeating sugar-phosphate backbone.
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