Question

18 15 16 17 7- What is the concentration of DNA whereby a 1:100 dilution has an observance reading of 0.015 at 260 nm? a. 6 ug mL b. 60 ug/mL c. 75 ug/mL d. 750 ug/mL 8- When measuring the concentration of RNA by spectrophotometry at 260 nm, the absorbance reading is multiplied by the dilution and a conversion factor of a. 20 6.30 c. 40 d. 50 9-DNA is isolated from a clinical sample. The absorbance at 260 nm is 0.489, and the absorbance at 280 nm is 0.257. Is this sample of sufficient quality for use in subsequent analysis? a. Yes b. No c. Cannot be determined with the given data. d. Can be determined with the given data 10- Isolation of RNA is difficult due to its ability to degrade quickly. What is the main reason for RNA being especially labile, or unstable? a. Stability of RNA at high temperature b. Negative charge of RNA c. Presence of RNAase d. Single strand nature of RNA

Answer 1

7. Answer is option C, 75ug/ml

formula is Concentration = (absorbance at 260/ pathlength) x conversion factor x dilution factor

= 0.015/1 x 50ug x 100 = 75ug/ml

8. Conversion factor for RNA at 260nm is Option C - 40,

this is the standard value for ssRNA at 260nm.

9. The calculation for estimating the purity or quality of DNA uses the

formula DNA purity (A260/A280) = 0.489 / 0.257 = 1.9

A good quality DNA will have a (A260/A280) ratio of 1.7 - 2.0,

According to this standard the DNA obtained from clinical sample is in the range of 1.7-2.0 (1.9), therefore it has sufficeint quality to be used for subsequent analysis.

10. Answer is option C - Presence of RNase

RNA has 2'-hydroxyl group on the pentose ring. This hydroxyl group makes RNA less stable than DNA because it is more susceptible to hydrolysis. And phosphodiester bonds form in liquid hence makes it unstable. Apart from this extractions of samples have RNase contaminations in the sample which is a main reason of RNA degradation