Consider the following segment of DNA:
       5'-...ATGCCAGTCACTGACTTG...-3'
       3'-...TACGGTCAGTGACTGAAC...-5'

How many phosphodiester bonds are required to form this segment of double-stranded DNA?

Key Concepts

Phosphodiester Bonds

Phosphodiester bonds are covalent linkages that connect the 5' phosphate group of one nucleotide to the 3' hydroxyl group of another nucleotide in a DNA strand. These bonds form the backbone of the DNA molecule, providing structural integrity and allowing for the formation of long chains of nucleotides. Each bond is crucial for maintaining the continuity of the DNA strand.

Double-Stranded DNA Structure

Double-stranded DNA consists of two complementary strands that run in opposite directions, known as antiparallel orientation. Each strand is composed of nucleotides linked by phosphodiester bonds, and the strands are held together by hydrogen bonds between complementary bases (adenine with thymine, and guanine with cytosine). Understanding this structure is essential for calculating the number of bonds in a given segment.

Counting Nucleotides

To determine the number of phosphodiester bonds in a segment of DNA, one must count the nucleotides present. Each nucleotide contributes one phosphodiester bond to the backbone, except for the last nucleotide on each strand, which does not form a bond with a subsequent nucleotide. Therefore, the total number of bonds is equal to the total number of nucleotides minus one for each strand.