Deoxyribonucleic acid (DNA)

In the syllabus and the exam

DNA is the molecular thread running from the cell structure chapter, where it is located inside the nucleus, through cell division, where it is copied before mitosis and meiosis, to genetics, where its sequence determines an organism's genes and alleles, so questions on DNA can appear anywhere across these connected chapters. Candidates at SPM level are expected to know that DNA has a double helix structure, that it is found packaged into chromosomes within the nucleus, that it carries the genetic instructions passed from parent to offspring, and that a gene is a specific section of a DNA molecule that codes for a particular characteristic or protein. A frequent error is confusing the terms DNA, gene and chromosome, treating them as interchangeable, when in the correct hierarchy a chromosome is a structure made of a very long, tightly coiled DNA molecule, and a gene is just one specific segment along that DNA molecule; candidates should be able to place all three terms in this order in a structured answer. Another common mistake is describing DNA as being found only in the nucleus, overlooking that a small amount of DNA is also present in mitochondria and chloroplasts, a detail occasionally tested in higher-order questions about cell organelles and inheritance. Candidates should also be able to state, in simple terms, that the sequence of bases along a DNA molecule is what ultimately determines the sequence of amino acids in a protein, giving a direct line from DNA structure to the physical characteristics an organism actually shows.

Example

A DNA molecule is shaped like a twisted ladder, or double helix, with two long strands held together by pairs of bases that carry the instructions for building and running an organism.

Related terms

ChromosomeGeneNucleus

Source:SRC-DSKP-EN