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At a wavelength of 260 nm, the average extinction coefficient for double-stranded DNA is 0.020 (μg/mL) −1 cm −1, for single-stranded DNA it is 0.027 (μg/mL) −1 cm −1, for single-stranded RNA it is 0.025 (μg/mL) −1 cm −1 and for short single-stranded oligonucleotides it is dependent on the length and base composition.
In biochemistry, the molar absorption coefficient of a protein at 280 nm depends almost exclusively on the number of aromatic residues, particularly tryptophan, and can be predicted from the sequence of amino acids. [6] Similarly, the molar absorption coefficient of nucleic acids at 260 nm can be predicted given the nucleotide sequence.
Once a reference signal is acquired, it is compared to the transmitted light Is of the measured sample. In order to calculate the associated extinction coefficient μ t, Beer's law can be applied as follows: I s = I o exp(-μ t d), where d is the sample thickness. The extinction coefficient is therefore: μ t = -ln(I s /I o)/d.
Sodium dodecyl sulfate (SDS), a common detergent, may be found in protein extracts because it is used to lyse cells by disrupting the membrane lipid bilayer and to denature proteins for SDS-PAGE. While other detergents interfere with the assay at high concentration, the interference caused by SDS is of two different modes, and each occurs at a ...
A variable pathlength cell is a sample holder used for ultraviolet–visible spectroscopy or infrared spectroscopy that has a path length that can be varied to change the absorbance without changing the sample concentration.
where λ is a wavelength, is the optical path length of the cuvette which contains the solution of the N compounds (chromophores), , is the molar absorbance (also known as the extinction coefficient) of the ith chemical species at the wavelength λ, c i is its concentration. When the concentrations have been calculated as above and absorbance ...
Extinction coefficient refers to several different measures of the absorption of light in a medium: Attenuation coefficient , sometimes called "extinction coefficient" in meteorology or climatology Mass extinction coefficient , how strongly a substance absorbs light at a given wavelength, per mass density
The following table is a representative sample of Erwin Chargaff's 1952 data, listing the base composition of DNA from various organisms and support both of Chargaff's rules. [17] An organism such as φX174 with significant variation from A/T and G/C equal to one, is indicative of single stranded DNA.