- Adenine (A) always pairs with Thymine (T).

- Guanine (G) always pairs with Cytosine (C).

- Uracil (U) pairs with Adenine (A) in RNA.

* Nucleotides are the building blocks of DNA and RNA. Each nucleotide consists of a sugar molecule, a phosphate molecule, and a nitrogenous base.

* The four nitrogenous bases used in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T).

* RNA contains uracil (U) instead of thymine.

* The sequence of nucleotides in a DNA or RNA molecule determines the genetic information it carries.

* The genetic information encoded in DNA and RNA is used by cells to produce proteins.

Proteins carry out most of the functions in the cell, including structural support, metabolism, and reproduction.

* The rules of complementary base pairing ensure that DNA and RNA molecules can form stable structures that can accurately store and transmit genetic information

* During DNA replication, the two strands of the double helix separate and each strand serves as a template for the synthesis of a new strand.

* New nucleotides are added to each strand in a complementary fashion, with A pairing with T and G pairing with C.

* This ensures that the two new DNA molecules are identical to the original molecule.

* During RNA transcription, one of the strands of DNA serves as a template for the synthesis of a new RNA molecule.

* New nucleotides are added to the RNA molecule in a complementary fashion, with A pairing with U, G pairing with C, and T pairing with A.

* This ensures that the RNA molecule has the same genetic information as the DNA molecule, but in a form that can be used to produce proteins.