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### Simple Formula to Calculate the number of phosphodiester bond in a DNA molecule with Practice problems

How to calculate the number of phosphodiester bond in a DNA molecule with Practice problems

1. How many phosphodiester bonds are present in the following DNA molecule?
5'-CTAGAG-3'
3'-GATCTC-5
a) 6  b) 11  c) 12  d) 10
Suppose, no. of base pairs in DNA is ‘n’
You can answer any question like this using the given formula
No. of base pairs =6
No. of phosphodiester bonds in a DNA molecule = 2n-2
Where n=No. of base pairs (bp)
=(2x6)-2=12-2=10
2. How many phosphodiester bonds are present in a DNA with 50 bp?
a) 100  b) 99  c) 200  d) 98
If the no. of base pairs in DNA is ‘n’
No. of base pairs=50
No. of phosphodiester bonds in a DNA molecule = 2n-2
=(2x50)-2=100-2=98

3. In a DNA molecule the no of phosphodiester bonds are 1200. Find the number of base pairs?
a) 600  b) 601  c) 602  d) 1199
If the no. of base pairs in DNA is ‘n’
No. of base pairs=?
No. of phosphodiester bonds in a DNA molecule = 2n-2
=2n-2=1200
2n=1200+2=1202
n=1202/2=601

4. How many phosphodiester bonds are present in a ssDNA with 50 bases?
a) 100 b) 99  c) 200  d) 49
No. of phosphodiester bonds in a single strand of DNA= n-1
Where n is the no. of bases/nucleotides (incase of single stranded DNA or RNA)
ssDNA =n-1 phosphodiester bonds
=50-1=49
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