Purine or pyrimidine bases of the two strands of DNA molecule are joined together by ... ................. bonds.

Explanation

To answer the question regarding how purine or pyrimidine bases of the two strands of a DNA molecule are joined together, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Components of DNA**: DNA is composed of two strands that run in opposite directions (anti-parallel) and are made up of nucleotides. Each nucleotide contains a sugar, a phosphate group, and a nitrogenous base.

2. **Understand the Types of Bases**: The nitrogenous bases in DNA are categorized into two groups: purines and pyrimidines. Purines include adenine (A) and guanine (G), while pyrimidines include cytosine (C) and thymine (T).

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