GC-content - Determination of GC Content

Determination of GC Content

GC content is usually expressed as a percentage value, but sometimes as a ratio (called G+C ratio or GC-ratio). GC-content percentage is calculated as

whereas the AT/GC ratio is calculated as

.

The GC-content percentages as well as GC-ratio can be measured by several means, but one of the simplest methods is to measure what is called the melting temperature of the DNA double helix using spectrophotometry. The absorbance of DNA at a wavelength of 260 nm increases fairly sharply when the double-stranded DNA separates into two single strands when sufficiently heated. The most commonly used protocol for determining GC ratios uses flow cytometry for large number of samples.

In alternative manner, if the DNA or RNA molecule under investigation has been sequenced then the GC-content can be accurately calculated by simple arithmetic or by using the free online GC calculator.