OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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What are chromosomes composed of?

Short pieces of RNA
Coiled DNA molecules
Proteins only
Fatty acids and proteins

The correct answer is: Coiled DNA molecules

Chromosomes are composed of coiled DNA molecules, which are organized and packaged together with proteins. This coiling and packing is crucial because it allows the long strands of DNA to fit into the cell nucleus, and the associated proteins help in structural support and regulation of gene expression. Each chromosome is made up of a single, very long molecule of DNA, which carries genetic information essential for the development, functioning, and reproduction of all living organisms. While proteins indeed play a role in the structure of chromosomes, coiled DNA is the primary composing element, making this answer the most accurate choice.