The Structure and Replication of DNA

Inside the nucleus of every cell is a molecule that carries the instructions for life. This molecule, called DNA, stores the information needed to build proteins and control cell activities. DNA is made of smaller units called nucleotides. Each nucleotide contains three parts: a sugar, a phosphate group, and a nitrogen base. There are four types of bases in DNA: adenine (A), thymine (T), cytosine (C), and guanine (G).

The structure of DNA is often described as a double helix, which looks like a twisted ladder. The sides of the ladder are made of alternating sugar and phosphate molecules. The “rungs” of the ladder are formed by pairs of nitrogen bases. These bases follow a specific pairing rule: adenine always pairs with thymine, and cytosine always pairs with guanine. This pattern is important because it allows DNA to store information in a consistent and organized way.

Before a cell divides, it must copy its DNA so that each new cell receives a complete set of instructions. This process is called DNA replication. During replication, the double helix unwinds and the two strands separate. The hydrogen bonds between the base pairs break, leaving each strand exposed.

Each original strand then serves as a template for building a new strand. Free nucleotides in the cell attach to the exposed bases following the base-pairing rules. For example, if one strand has a sequence of A-T-C, the new strand will form with T-A-G. Enzymes help join the nucleotides together to form the new strands.

At the end of replication, two identical DNA molecules are formed. Each molecule contains one original strand and one newly made strand. This ensures that genetic information is passed from one cell to the next with high accuracy. Because of this process, cells can divide and organisms can grow, repair damage, and reproduce.