Question

If there are 20 nucleotides in a polynucleotide chain, then what is the number of phosphodiester bonds?

• A. 21
• B. 20
• C. 19
• D. 18

Hint:

Remember, in polynucleotides, the phosphodiester bond connects the 3' carbon of one nucleotide to the 5' carbon of the next nucleotide, forming a long chain of nucleotides.

Answer 1

The Correct Option is C

A polynucleotide chain is composed of nucleotides linked together through phosphodiester bonds. In such a sequence, each nucleotide is connected to the next by a phosphodiester bond. If there are 20 nucleotides in the chain, the number of phosphodiester bonds can be calculated by understanding that:

• The first nucleotide does not connect to any previous nucleotide, so no phosphodiester bond is needed before it.
• Each subsequent nucleotide (from the second onward) forms one phosphodiester bond to the previous nucleotide.

Therefore, the number of phosphodiester bonds is equal to the number of nucleotides minus one:

Number of phosphodiester bonds = Number of nucleotides - 1

For 20 nucleotides:

Number of phosphodiester bonds = 20 - 1 = 19

Thus, the correct answer is 19.