Pearson Edexcel · GCSE · Biology
Course version: 1BI0 · Version from Sept 2016
Describe DNA as a polymer made up of: a two strands coiled to form a…
Full specification wording
Topic 3 – Genetics: 3.4 Describe DNA as a polymer made up of: a two strands coiled to form a double helix b strands linked by a series of complementary base pairs joined together by weak hydrogen bonds c nucleotides that consist of a sugar and phosphate group with one of the four different bases attached to the sugar
DNA is a polymer — a large molecule built from many repeating units called nucleotides.
Checked against the Pearson Edexcel 1BI0 specification (opens in a new tab) on .
- Point 2 of 20
Study notes
From the checked teaching notes for this specification point.
The idea
DNA is a polymer — a large molecule built from many repeating units called nucleotides. Each nucleotide has three parts: a sugar, a phosphate group, and one of four different bases attached to the sugar. The nucleotides join to form two strands. These two strands are coiled together to make the double helix shape. The two strands are held together because bases on one strand pair with complementary bases on the other, and each base pair is joined by weak hydrogen bonds. So a good description covers all three ideas: the double helix of two coiled strands, the complementary base pairs held by weak hydrogen bonds, and the nucleotide made of sugar, phosphate and one of four bases.
What earns the marks
- DNA is a polymer made of many nucleotides.
- A nucleotide consists of a sugar, a phosphate group and one of four different bases attached to the sugar.
- DNA has two strands coiled to form a double helix.
- The two strands are linked by complementary base pairs.
- Base pairs are joined by weak hydrogen bonds.
Common mistakes and how to put them right
Saying DNA has a single strand.
Put it right: It has two strands coiled into a double helix.
Describing strong covalent bonds between the base pairs.
Put it right: The base pairs are joined by weak hydrogen bonds.
Leaving out the phosphate group when describing a nucleotide.
Put it right: A nucleotide is sugar, phosphate and a base.
Saying there are two bases.
Put it right: There are four different bases, one attached to each sugar.
Exam tips
- Use the three-part structure: nucleotide, double helix, base pairing.
- Name the bond as a weak hydrogen bond.
- State that there are four different bases and that pairing is complementary.
Try the lesson
The start of the Topic 3 – Genetics: 3.4 Describe DNA as a polymer made up of: a two strands coiled to form a double helix b strands linked by a series of complementary base pairs joined together by weak hydrogen bonds c nucleotides that consist of a sugar and phosphate group with one of the four different bases attached to the sugar lesson, made from checked teaching notes for this specification point.
Have a go first
Which three components together make up a single nucleotide in a DNA molecule?
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