1. Questions

Biology

9. The restriction endonuclease AluI leaves blunt ends on DNA fragments after digestion. These blunt ends
a) form hydrogen bonds with the blunt ends of other fragments produced by AluI
b) are fully base paired
c) have only one unpaired base
d) always include the base adenine
e) require a polymerase enzyme to bond them to the other blunt ends
MY ANSWER: d

10. You digest a piece of DNA that is 49000 base pairslong, with a restriction endonuclease having a recognition site four base pairs long. Approxiamately, how many fragments would you expect to be produced?
a) 20
b)98
c)192
d) 256
e)331
MY ANSWER: e
11. Consider the ends of the DNA fragments shown below . They have been produced by digestion of a single sequence of DNA usinga number of restriction endonucleases
1) 5’A 3’
3’TTCGA5’
2) 5’G 3’
3’CAGCT5’
3) 5’AATTC3’
3’ G5
4) 5’TCGAC
3’ G5’3’
5) 5’GGG3’
3’CCC 5’

Which of these ends are capable of annealing and being joined by DNA ligase?
a) 1 and 2
b) 1 and 5
c) 2 and 4
d) 5 and 3
e) 3 and 4
MY ANSWER: d

12. By mistake, DNA fragments were loaded onto a gel using a buffer with a PH so low that all the phosphate groups of the DNA nucleotides were protonated (i.e…had H+ ions added to them.) Subsequent electrophoresis failed to separate the fragments. This was because
a) the voltage difference across the gel was inadequate
b) the double- stranded fragments became single-standed and all migrated very swiftly to the positive pole
c) the fragments joined together into one huge molecule
d) the fragments had very little charge, and thus were not attracted to the positive pole
e) the fragments became circular

MY ANSWER: b

13. Restriction endonuclease digestion of a DNA sequence yielded fragments to the following size
1) 5.2kb
2)0.8kb
3)1.2kb
4)3.8kb
5)3.1kb
After gel electrophoresis, what would be the order in which these fragments would be found- --the last fragment listed being the furthest from the negative pole.
a) 1,2,5,4,3
b) 2,3,4,5,1
c) 1,3,5,2,4
d) 3,2,4,5,1
e) 1,4,5,3,2
MYANSWER: e