Answer the following DNAgenome questions a A dsDNA molecule

Answer the following DNA/genome questions
a) A dsDNA molecule is analyzed and found to have 16% G content. What are the percentages of each remaining base in this molecule?
b)Some viruses carry their genome as RNA instead of DNA. In some viruses, this RNA is double stranded, and in some it is single stranded. Virus particles from two different RNA viruses were purified, their genomes were extracted and analyzed for purine base content. One virus had 18% A and 22% G; the second virus had 32% A and 18% G. Which of these viruses must have a single stranded genome?
c)Which of the following sequences is the most likely candidate to be recognized by a restriction enzyme?

1. TTCCAAGG

2. AGGCCT     

3. ATTCCG        

4. TATGCG         

5. ATGC

Solution

a. We have to apply the Chargaff\'s rule to find out the percentage of Nucleotides in any given dsDNA. Chargaff\'s rule is very simple, which states that

A+G=C+T (amount of purines is always equal to amount of pyrimidines)

hence the total percentages of nucleotides in any given dsDNA is equal to 100%. In the above question it is clear that the Guanine is 16%, hence the amount of Cytosine is also 16% since Guanine always binds to Cytosine with triple bonds. Lets apply Chargaff\'s rule,

A+G=C+T

A+G+C+T=100%

A+16+16+T=100%

A+T=100-32

A+T=68

Adenine always binds to thymine with a double bond, hence amount of adenine is equal to amount of thymine. So adenine constitute 34% and thymine consitutes about 34%.

So the amount of other bases is Adenine=34%, Cytosine=16% thymine= 34%.

b. This questoin is also based on the Chargaff\'s rule, which states that the total base percentage is equal to 100, i.e if amount of Adinine, Guanine, cytosine and thymine (Uracil as in RNA) is added, it sums to 100%.

In the above question,

Virus-1 has, 18% of Adenine, and 22% Guanine. ( by rule Uracil must also be 18% and Cytosine must be 22% in any double stranded RNA)

A+G+C+U=100%

Let us substitute the amount of bases,

i.e A=18, G=22 U=18 and C=22, if we add all the 4 bases, 18+22+18+22=80. which does not satisfy the Chargaff\'s rule becuase the amount of bases is not equal to 100%.

Virus-2 has, 32% of Adenine, and 18% Guanine. ( by rule Uracil must also be 32% and Cytosine must be 18% in any double stranded RNA)

A+G+C+U=100%

Let us substitute the amount of bases,

i.e A=32, G=18 U=32 and C=18, if we add all the 4 bases, 32+18+32+18=100. which satisfies the Chargaff\'s rule becuase the amount of bases is equal to 100%.

Therefore Virus-1 has single stranded RNA and Virus-2 has Double stranded RNA.

c. Resrtiction Enzymes always recognises the palindromic sequences, i.e sequence which reads same from both the 5\' and 3\' end. if we look at the above options, OPTION 2 is a perfect palindromic sequence. only option 3 is a perfect sequence recognised by the restriction enzymes.