8- The same DNA strand is added to three tubes. Each tube contains environmental
ID: 143140 • Letter: 8
Question
8- The same DNA strand is added to three tubes. Each tube contains environmental conditions that are similar to the other tubes with the exceptions listed below. Tube 1 and 2 are incubated at 35°C while tube 3 is incubated at 90°C Tube 2 is at pH 6 while tubes 1 and 3 are at pH 13. Tube 3 contains 10mM KCI while tubes 1 and 2 contains 1mM KCI. You then add the DNA solutions to cuvettes and stick them in a spectrophotometer set to 260nm. For which tube do you expect to see the highest absorbance value? A. Tube 1 B. Tube 2 Questions 9-11 apply to the data bellow.Explanation / Answer
8. DNA is made up of AT and GC base pairs. As temperature increases, the DNA starts unwinding. AT base pairs melt at 700C while GC base pairs melts over 1000C. Hence, AT rich basepair regions will unwind faster than GC rich regions. When both strands of DNA unwind and separate, it is known as denaturation. Melting temperature (Tm) is the temperature, at which DNA is half-unwound. This Tm is around 900C for naturally occurring DNA.
When DNA is exposed to high concentration of alkali, there is breakage of phosphodiester bonds as well as breakage of hydrogen bonds between nitrogen bases, resulting in denaturation. Moderate alkali concentrations will cause the disruption of hydrogen bonding between base pairs and deprotonation. Neutral pH will allow the hydrogen bonds to reform. A slightly acidic pH of 6 will not denature DNA. However, high pH of 13 will cause denaturation of DNA.
DNA is a polyanionic molecule. Low concentration of salt will favor denaturation. At high salt, the negative charges of phosphate present in DNA is shielded by the cations. Hence, the repulsive forces between the antiparallel strands of DNA are removed. 10 mM KCl is higher than 1 mM KCl. Hence, 1 mM KCl will favor denaturation while 10 mM KCl will favor renaturation.
Denatured DNA absorbs more ultra violet light than double stranded DNA. This is due to the stacking interaction between bases in double stranded DNA.
Tube 1: 350C, pH 13 and 1mM KCl
pH 13 and 1 mM KCL will induce denaturation but 350C will promote renaturation.
Tube 2: 350C, pH 6 and 1mM KCl
1mM KCl promotes denaturation, while 350C will not (as temperature is lower than Tm). The pH 6 will also favor renaturation.
Tube 3: 900C, pH 13 and 10 mM KCl
As 900C is the Tm of DNA, it will cause denaturation. Similarly, pH 13 will also cause denaturation. However, 10 mM KCl will cause renaturation.
Tube 3 will have highest absorbance, as higher temperature increase rapidly denatures DNA. As denaturation is fastest in tube 3, it will have the highest absorbance. Along with it, an extreme pH will also induce denaturation. Salt will have lowest effect on DNA.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.