Guaninecytosine

Guanine-cytosine refers to the base pairing between guanine (G) on one strand and cytosine (C) on the complementary strand of DNA or RNA. Guanine is a purine and cytosine a pyrimidine; together they form a strong, highly stable pair connected by three hydrogen bonds in standard Watson-Crick geometry. This pairing is one of the two canonical base-pairing schemes in nucleic acids, the other being adenine with thymine (in DNA) or adenine with uracil (in RNA).

In double-stranded nucleic acids, G-C pairs contribute significantly to helix stability. The three hydrogen bonds, along with favorable base-stacking interactions, make G-C-rich regions more thermostable than regions rich in A-T (or A-U) pairs, which have two hydrogen bonds. The relative abundance of G and C nucleotides influences the overall melting temperature of the molecule and can affect the structure and dynamics of the nucleic acid.

GC content is the percentage of nucleotides in a DNA or RNA molecule that are either guanine or cytosine. Variation in GC content across genomes influences DNA stability, replication, and gene density. GC-rich regions often correlate with regulatory elements such as promoters and CpG-rich islands in vertebrates, though patterns vary among organisms and genomic regions. In laboratory settings, extreme GC content can pose challenges for polymerase chain reactions, sequencing, and cloning due to amplification biases and temperature requirements.

Guanine-cytosine pairing is a fundamental, conserved feature of genetic information storage and transfer, with broad implications for biology and biotechnology.