BIOD 101 Module 4 Problem Set

BIOD 101 Module 4 Problem Set Compare and contrast purines and pyrimidines and provide examples of each. Answer: Purines contain two carbon-nitrogen rings and four nitrogen atoms, while the pyrimidines contain one carbon-nitrogen ring and two nitrogen atoms. Adenine and guanine are purines, and thymine and cytosine are pyrimidines (See section 4.1 in module). Describe the structure and arrangement of DNA. Answer: DNA is a double helix, which means it is composed of two helical strands. The two strands are held together by the ‘rungs’, which are madeof complementary pairs. The pairs are held together by weak hydrogen bonds. Just as the nucleotides are paired in a complementary fashion, the strands are also arranged in a complementary- type pattern and are said to be antiparallel. In this antiparallel arrangement, the strands are oriented with one strand being in the 5’→3’ orientation and the other strand inthe 3’→5’ orientation (See section 4.1 in module).