Question

1. What is an absorption spectrum? 2. In what two ways is spectrophotometry useful? 3. What is an extinction coefficient? 4. Why do proteins have a ower extinction coeficiant hn nudeclc cd that all proteins have the same extinction coefficient? Why or why not?

Answer 1

1.An Absorption spectrum is a spectrum of radiant energy whose intensity at each wavelength is a measure of the amount of energy at that wavelength that has passed through a selectively absorbing substance.

The absorption of radiation by a substance can be quantified with an instrument called a Spectrophotometer.

In 1881 German plant physiologist T.W. Engelmann placed a filamentous green algae under the microscope and illuminated it with a tiny spectrum of visible light.And he observed that bacteria congregated around the portion of filament illuminated by red and blue light.

2.The use of spectrophotometry is you can glean a lot of useful information based on how things interact with light.The most common uses for spectrophotometry for which I'm aware is for determining concentration and giving clues to chemical structure

The best use for simple spectrophotometry is determining an unknown concentration of a known compound. As it turns out absorption or transmittance varies linearly with molar concentration of a compound.

3.Extinction coefficient refers to several different measured of the absorption of light in a medium.

  •Attenuation coefficient, called extinction coefficient in meteorology or climatology

  •Mass extinction coefficient,how strongly a substance absorbs light at a given wavelength,per mass density.

  •Molar extinction coefficient, how strongly a substance absorbs light at a given wavelength,per molar concentration

4.This because the nucleic acids that make up DNA and RNA absorb strongly at 260nm.A ratio of about 2.0 is considered "pure" for RAN while a ratio of 1.8 is considered "pure" for DNA .Lower ratios indicate the presence of protein.