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DNA stands for deoxyribonucleic acid. The four bases in DNA are adenine (A), thymine (T), guanine (G) and cytosine (C). Free GCSE Biology notes and 11 FAQs.
The Structure of DNA is part of Reproduction in GCSE Edexcel Higher Biology.
3 min
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GCSE Edexcel Higher
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DNA stands for deoxyribonucleic acid. The four bases in DNA are adenine (A), thymine (T), guanine (G) and cytosine (C). Free GCSE Biology notes and 11 FAQs.
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Use this lesson to stay inside Reproduction while connecting the detail back to the wider Topic 3: Genetics topic.
Read the core explanations from The Structure of DNA before testing yourself from memory.
Your DNA contains the instructions for everything about you - your eye colour, height, even how your cells make proteins. But what exactly is this molecule that carries such important information?
Think of DNA like a very long necklace made from just four different types of beads. These 'beads' are called nucleotides, and they're the building blocks that repeat over and over to make the DNA polymer.
Trap: Many students think DNA is made of amino acids like proteins. Actually, DNA is made of nucleotides - completely different building blocks with a sugar-phosphate backbone.
DNA contains exactly four different bases. These are the 'letters' of the genetic code, and their sequence determines what information the DNA carries.
The four bases are:A - AdenineT - ThymineG - GuanineC - Cytosine
Remember them with the phrase: "All Teachers Get Coffee" (A, T, G, C). Each base attaches to the sugar part of a nucleotide, making four different types of nucleotide possible.
Picture DNA as a twisted ladder. The sides of this ladder are made from alternating sugar and phosphate sections - this forms the backbone of DNA.
The pattern repeats: sugar → phosphate → sugar → phosphate → sugar → phosphate, and so on. Attached to each sugar is one of the four bases (A, T, G, or C). This creates the sequence that stores genetic information.
The sugar-phosphate backbone is the same throughout DNA - only the bases change. It's like having identical lamp posts (the backbone) with different coloured lights (the bases) attached to each one.
DNA doesn't exist as a single strand - it forms a double helix with two complementary strands. The bases on opposite strands pair up in a very specific way.
The base pairing rules are:A always pairs with TC always pairs with G
Think of it like a zip - the teeth on one side only fit with specific teeth on the other side. If one strand has the sequence ATCG, the opposite strand must be TAGC.
Worked example: Finding the Complementary DNA Sequence
If one DNA strand has the sequence ATCGTA, what is the sequence of the complementary strand?
Answer: TAGCAT
DNA questions appear regularly in GCSE exams. Here's how to tackle them and avoid the most common pitfalls.
Exam depth extension: In the structure of dna, connect what is dna made of? to the four dna bases using clear cause-and-effect statements. When you explain biological processes, include what changes, why it changes, and the consequence for cells, organisms, or populations. If calculations appear, show each step, include units, and end with a sentence that interprets the result in biological context.
Command word focus: When asked to 'describe' DNA structure, state what it's made of and how it's arranged. When asked to 'explain' base pairing, give the rules AND why they're important for DNA replication.
Mark-winning phrases:"DNA is a polymer made from nucleotides""Each nucleotide consists of a sugar, phosphate group and base""The backbone consists of alternating sugar and phosphate groups""Complementary base pairing: A with T, C with G"
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
DNA stands for deoxyribonucleic acid. It is a polymer made from four different nucleotides that stores genetic information in cells.
The sugar-phosphate backbone is the side of the DNA ladder, made from alternating sugar and phosphate sections. It is the same throughout DNA, and one of the four bases (A, T, G or C) is attached to each sugar.
The four bases in DNA are adenine (A), thymine (T), guanine (G) and cytosine (C). They are the letters of the genetic code, and their sequence determines what information the DNA carries. A memory phrase is All Teachers Get Coffee.
Complementary base pairing is the specific pairing of DNA bases on opposite strands, where adenine (A) always links to thymine (T) and cytosine (C) always links to guanine (G). So if one strand has the sequence ATCG, the opposite strand must be TAGC.
DNA is a polymer made from four different nucleotides. The nucleotides are the repeating units, like beads on a very long necklace, and they repeat over and over to make the DNA polymer.
A double helix is the structure of DNA: two complementary strands twisted together like a twisted ladder. The bases on opposite strands pair up, with A pairing with T and C pairing with G.
The sugar in DNA is deoxyribose. Each nucleotide consists of a deoxyribose sugar, a phosphate group and one of four bases attached to the sugar.
Adenine (A) always pairs with thymine (T) on the opposite DNA strand, and cytosine (C) always pairs with guanine (G). This is called complementary base pairing.
DNA is made of nucleotides, not amino acids like proteins. Nucleotides are completely different building blocks, joined to form a sugar-phosphate backbone with bases attached.
To find a complementary DNA strand, go through the original sequence base by base: A pairs with T, T with A, C with G and G with C. For example, the complementary strand to ATCGTA is TAGCAT.
The four DNA bases can be remembered with the phrase "All Teachers Get Coffee" for A, T, G and C. These stand for adenine, thymine, guanine and cytosine, the letters of the genetic code.