Numerical Problems/ISC/Class 12
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
Numerical Problems - Biotechnology
A plasmid DNA is 5000 base pairs (bp) long. A restriction enzyme EcoRI recognizes a 6-base pair recognition sequence. Assuming the bases are randomly distributed and occur with equal frequency, approximately how many EcoRI recognition sites would you expect to find in this plasmid?
Solution:
The probability of finding a specific 6-base pair sequence (like EcoRI's GAATTC) is (1/4)^6, since there are 4 possible bases (A, T, C, G) at each position.
Probability = (1/4)^6 = 1/4096
Expected number of sites = (Length of DNA) / (Probability of recognition sequence) Expected number of sites = 5000 bp / 4096 bp/site ≈ 1.22 sites
Therefore, you would expect to find approximately 1 or 2 EcoRI recognition sites in this plasmid.
You have 100 ng of a plasmid vector (5 kb) and you want to ligate an insert DNA fragment (1 kb) into it. For optimal ligation, a vector:insert molar ratio of 1:3 is desired. How much insert DNA (in ng) should you add to the ligation reaction?
Solution:
First, calculate the moles of vector DNA:
Moles of vector = (Mass of vector in ng) / (Molecular weight of vector in ng/mole) Molecular weight is proportional to size in kb.
Moles of vector (relative) = 100 ng / 5 kb = 20 ng/kb
Now, calculate the desired moles of insert DNA based on the 1:3 molar ratio:
Desired moles of insert (relative) = 3 * Moles of vector (relative) Desired moles of insert (relative) = 3 * 20 ng/kb = 60 ng/kb
Finally, calculate the mass of insert DNA needed:
Mass of insert = Desired moles of insert (relative) * Size of insert in kb Mass of insert = 60 ng/kb * 1 kb = 60 ng
Therefore, you should add 60 ng of insert DNA to the ligation reaction.
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