Phase-contrast microscopy generates image in which degree of darkness or brightness of a region of specimen depends on the refractive index of that region.

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#Unit 13. Methods in Biology

In a chiral medium the molar absorptivity of LCP and RCP light are different so they will be absorbed by the medium in different amounts. 

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#Unit 13. Methods in Biology

Differential absorption of the two circularly polarized lights resulted in elliptically polarized light and CD is represented in terms of molar ellipticity(θ).

θ = 3298    ϵ

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#Unit 13. Methods in Biology

β-sheets shows a negative bands at 218nm and a positive one at 196nm.

Random coils has a positive band at 212nm and a negative one around 195nm.

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#Unit 13. Methods in Biology

CD can be used to estimate the structure of unknown proteins and monitor conformational changes due to temperature, mutations, heat, denaturants or binding interactions

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#Unit 13. Methods in Biology

CD spectra is used to

determine whether proteins are properly folded, 

estimate the fraction of the protein that is folded in either of the common secondary structures, and

monitor transitions between the folded and unfolded states.

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#Unit 13. Methods in Biology