1.) A restriction recognition site is repeated 1 times on a circular DNA molecul
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Question
1.) A restriction recognition site is repeated 1 times on a circular DNA molecule. If you treat this DNA molecule with this restriction enzyme, how many DNA fragments will you get?
a. 1
b. 2
c. 3
d. Restriction enzyme does not cut a circular molecule
2.) In an agarose gel DNA electrophoresis, the DNA fragments are separated based on their
a. Size
b. Electrical charge
c. Nucleotides sequences
d. Density
e. All of the above
3.) DNA molecules are usually separated using agarose gel rather than polyacrylamide because:
a. Agarose polymerizes faster than acrylamide gel
b. Polyacrylamide gel has pore size larger than the size of DNA molecules
c. Agarose gel do not have pores on tis matrix and can hold large DNA molecules
d. Agarose gel has larger pore size similar to the size of DNA molecules
4.) Restriction endonucleases
a. Randomly recognize and cut DNA sequences
b. Hydrolysis the phosphodiester bond of DNA backbone
c. Recognize specific sequence on double stranded DNA
d. A and B
e. B and C
Explanation / Answer
1) Option 'b' is the correct answer.
2 fragments will be formed if a DNA containing 1 repeat of retriction recognition site is treated with a restriction enzyme. When a restriction enzyme comes in contact with its target sequence, it will make a double stranded cut in the DNA molecule. If the restriction site is repeated only once in a circular plasmid, it means that there are 2 target sequences in the circular DNA for enzyme. Thus, the restriction enzyme will make cuts at 2 sites in the circular DNA to yeild 2 separate DNA fragments.
2) Option 'a' is the correct answer.
In agarose gel electrophoresis, DNA fragments are separated according to their size. A solution of DNA molecules is placed in a gel. Because each DNA molecule is negatively charged, it can be pulled through the gel by an electric field. Small DNA molecules move more quickly through the gel than larger DNA molecules.
3) Option 'd' is the correct answer.
Agarose gel has a pore size simialar to DNA molecule of size around 100 bp and 25 kb. DNA fragments smaller than 100 bp are more effectively separated using polyacrylamide gel electrophoresis. A polyacrylamide gel is thinner and has a lower pore siz. Polyacrylamide gels have a rather small range of separation, but have very high resolving power.
4) Option 'e' is the correct answer.
Restriction endonucleases recognize particular base sequences, called recognition sequences or recognition sites, in their target DNA and cleave that DNA at defined positions. The fundamental reaction catalyzed by restriction endonucleases is the hydrolysis of the phosphodiester backbone of DNA. Specifically, the bond between the 3? oxygen atom and the phosphorus atom is broken. The products of this reaction are DNA strands with a free 3?-hydroxyl group and a 5?-phosphoryl group
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