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Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
The key difference
DNA is a double-stranded molecule containing deoxyribose sugar that stores genetic information. RNA is a single-stranded molecule containing ribose sugar that carries the genetic code from the nucleus to ribosomes for protein synthesis.
DNA and RNA are both nucleic acids made of nucleotide building blocks, but they have important structural differences that relate to their distinct functions. At IGCSE level (Extended curriculum), you need to know the key structural and functional differences between these two molecules.
A–T and C–G (complementary base pairing holds strands together)
No base pairing within the molecule (single strand)
Location
Nucleus (in chromosomes)
Made in the nucleus, moves to the cytoplasm (ribosomes)
Function
Long-term storage of genetic information; carries the genetic code
Carries a copy of the genetic code from the nucleus to ribosomes for protein synthesis
Relative size
Very long molecules
Much shorter than DNA
Why DNA Is Double-Stranded
The double-stranded structure of DNA provides several advantages:
Stability: the two strands are held together by hydrogen bonds between complementary bases (A–T and C–G), making the molecule chemically stable for long-term storage of genetic information
Accurate replication: when DNA replicates before cell division, each strand acts as a template for building a new complementary strand, ensuring the genetic code is copied accurately
Error detection: if a base on one strand is damaged, the complementary strand can be used to repair it
The Role of RNA in Protein Synthesis
DNA cannot leave the nucleus because chromosomes are too large to pass through nuclear pores. Instead, a copy of the gene's code is made as a molecule of messenger RNA (mRNA). This mRNA is single-stranded and small enough to pass through nuclear pores into the cytoplasm, where it attaches to a ribosome. The ribosome reads the mRNA code and assembles amino acids in the correct order to build a specific protein.
Note: at IGCSE level you need to know that RNA carries the genetic code from nucleus to ribosome. The detailed mechanism of transcription and translation is an A-level topic.
Try a comparison question (3 marks)
State three differences between the structure of DNA and RNA. [3]
Show the answer and marking guidance
DNA is double-stranded; RNA is single-stranded
DNA contains the base thymine (T); RNA contains uracil (U) instead
DNA contains deoxyribose sugar; RNA contains ribose sugar
Original Cambridge-style practice written for this site.
Common comparison mistakes
When answering a compare question, write matched pairs rather than two separate descriptions.
Saying RNA contains thymine: RNA has uracil (U) instead of thymine (T)
Confusing ribose and deoxyribose: deoxyribose is in DNA (the "D"), ribose is in RNA
Claiming DNA leaves the nucleus: DNA stays in the nucleus; RNA carries the message out
Saying DNA is "the genetic code" while RNA "does nothing": RNA is essential for protein synthesis