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#molar absorptivity

2 public questions tagged with this topic.

What is the correct absorbance for a 0.1 mM solution with ε=6220 and l=0.5 cm?

Numerical application of Beer-Lambert law enables concentration or absorbance prediction using A equals ε c l. Given ε 6220 M-1 cm-1 characteristic of NADH at 340 nm, c 0.1 mM which equals 1×10^-4 molar, and path length 0.5 cm, multiplication proceeds: 6220 times 1e-4 equals 0.622, multiplied by 0.5 equals 0.311. Rounded to two decimals yields 0.31 absorbance units within optimal photometric accuracy range. Such calculations essential for enzymology, monitoring NADH formation, adjusting substrate levels to maintain linearity and avoid detector saturation while ensuring measurable signal change for kinetic quantification.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

The molar absorptivity of tryptophan is approximately:

Molar extinction at 280 nm for individual aromatic amino acids determined from free amino acid spectra in neutral pH water. Published values approximate phenylalanine 200, tyrosine 1490, tryptophan 5500-5600 M-1 cm-1, making tryptophan strongest contributor to protein A280. Variations arise from solvent polarity, pH and nearest neighbor effects in polypeptide chain. Among provided choices 3000 represents order magnitude closest to true value, emphasizing tryptophan dominance compared with others near 1000-2000. Knowledge of these coefficients enables calculation of protein extinction from sequence using Edelhoch method, essential for concentration determination without standard curve.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.