It is the increase in absorbance (optical density ) of a material .Heat denaturation of DNA also called as melting causes the double helix structure to unwind to form a single strandard DNA. So, by the help of hyperchromicity one can distinguish between ss DNA and ds DNA .
Double stranded DNA denatures to form single stranded DNA and double stranded DNA absorbs less light (260nm wavelength). Therefore, when you take absorbance measurements of DNA that is converting from double to single strands (denaturing), you can see a rise in absorbance. Similarly, you can measure this effect as single strands re-anneal to become double strands, resulting in lower absorbance. The reason for the 'hyperchromatic shift' is that the aromatic rings of the nucelotide bases which absorb light energy at wavelengths of 260nm are partially hidden within the double stranded configuration. When the strands are separated, the bases are exposed and more readily absorb light.When DNA in solution is heated above its melting temperature (more than 80 c the ds DNA unwinds to form single strandard DNA. The bases become unstacked and can thus absorb light in the 260 nm wavelength region .When the bases becomes unstacked the wavelength of maximum absorbance doesnot change , but the amount absorbed by 37% . A double strand DNA dissociating to single strands produces a sharp cooperative transition .
Absorbance (A) is typically monitored at 260 or 280 nm for nucleic acids. Wavelength selection depends on nucleobase composition. GU‐ and AU‐rich sequences have maximum hyperchromicity at 260 nm and hyperchromicity near 0 at 280 nm; maximal hypochromicity for GC‐rich structures, on the other hand, occurs at 280 nm, although significant hypochromicity persists at 260 nm .
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Q. Hyperchromicity is -
a. Decrease of absorbance
b. Shift in UV upon hydrolysis
c. Increase in absorbance at 260 nm wavelength upon denaturation
d.Renaturation of ss DNA
Ans. c
Explanation - Absorbance of DNA is mainly due to nitrogen bases .Upon denaturation nitrogen bases exposed to the surface due to unstacked bases the absorbance increases . (Base stacking effect )
Q2. DNA shows hyperchromicity on
Double stranded DNA denatures to form single stranded DNA and double stranded DNA absorbs less light (260nm wavelength). Therefore, when you take absorbance measurements of DNA that is converting from double to single strands (denaturing), you can see a rise in absorbance. Similarly, you can measure this effect as single strands re-anneal to become double strands, resulting in lower absorbance. The reason for the 'hyperchromatic shift' is that the aromatic rings of the nucelotide bases which absorb light energy at wavelengths of 260nm are partially hidden within the double stranded configuration. When the strands are separated, the bases are exposed and more readily absorb light.When DNA in solution is heated above its melting temperature (more than 80 c the ds DNA unwinds to form single strandard DNA. The bases become unstacked and can thus absorb light in the 260 nm wavelength region .When the bases becomes unstacked the wavelength of maximum absorbance doesnot change , but the amount absorbed by 37% . A double strand DNA dissociating to single strands produces a sharp cooperative transition .
Absorbance (A) is typically monitored at 260 or 280 nm for nucleic acids. Wavelength selection depends on nucleobase composition. GU‐ and AU‐rich sequences have maximum hyperchromicity at 260 nm and hyperchromicity near 0 at 280 nm; maximal hypochromicity for GC‐rich structures, on the other hand, occurs at 280 nm, although significant hypochromicity persists at 260 nm .
Image source credit -https://in.pinterest.com/pin/490962796855257835/
Q. Hyperchromicity is -
a. Decrease of absorbance
b. Shift in UV upon hydrolysis
c. Increase in absorbance at 260 nm wavelength upon denaturation
d.Renaturation of ss DNA
Ans. c
Explanation - Absorbance of DNA is mainly due to nitrogen bases .Upon denaturation nitrogen bases exposed to the surface due to unstacked bases the absorbance increases . (Base stacking effect )
Q2. DNA shows hyperchromicity on
a.heating
b.cooling
c.crystallizing
d.lyophilizing
Ans. Heating
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