DNA as genetic code in living organisms

Summary

DNA (deoxyribonucleic acid) is the molecule that carries the genetic code in living organisms. It is found in most cells (such as skin, muscle, and nerve cells) and contains instructions that cells use to make proteins, many of which are enzymes. DNA is inherited from parents, so children share traits with them; a person’s DNA is a combination of DNA from both parents. Structurally, DNA is a double helix made of two polynucleotide strands, with “rungs” formed by nucleotide base pairs. In DNA, adenine (A) pairs only with thymine (T), and cytosine (C) pairs only with guanine (G), held together by hydrogen bonds. This base-pairing creates a code written in the order of bases. Genes are sections of DNA that contain instructions for making proteins. Because DNA stays in the nucleus, cells copy DNA information into RNA (such as mRNA), which ribosomes read using codons (triplets of bases) to assemble amino acids into proteins; tRNA helps match amino acids to codons. DNA can be copied through DNA replication, and errors during copying can cause mutations (such as deletions, insertions, substitutions, or duplications), which may be harmful, neutral, or beneficial and can drive evolution. Cells also use multiple repair mechanisms to fix DNA damage.

Key Points

• 1

  DNA stores genetic instructions in a double-helix structure and is inherited from parents.

• 2

  Base pairing follows A–T and C–G rules, and the order of bases forms genetic “codes” used to make proteins.

• 3

  DNA replication and mutations (plus DNA repair systems) are central to heredity, variation, and evolution.