DNA structure, replication, and genetic information

DNA as genetic code in living organisms

DNA (deoxyribonucleic acid) is the genetic code molecule found in living organisms. It is present in most cells (such as skin, muscle, and nerve cells) and is inherited from parents. DNA is made of two polynucleotide strands arranged as a double helix, where each “rung” consists of paired nitrogen bases. The base-pairing rules are A with T and C with G, held together by hydrogen bonds, allowing DNA to store information in the order of these bases. DNA instructions are used to make proteins, often through enzymes. Genes are DNA sections that contain instructions for producing polypeptides. Because DNA stays in the nucleus, cells copy (transcribe) DNA into RNA—especially messenger RNA (mRNA)—which can leave the nucleus and be read by ribosomes. Ribosomes translate mRNA codons (triplets of bases) into amino acids, with transfer RNA (tRNA) helping match amino acids to codons. DNA replication copies the double helix by separating strands and using base pairing to build new complementary strands; errors during copying can cause mutations, which may be harmful, neutral, or beneficial and can drive evolution. Cells also repair DNA damage using different enzyme-based pathways, depending on the type of damage (such as mismatched bases, chemical damage, UV damage, or double-strand breaks). The overall understanding of DNA’s role in heredity and its structure was built through key experiments and discoveries, including the identification of DNA as genetic material and the development of the double-helix model.

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DNA double helix and nucleotide pairing

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