This course is part of a series taught by Kevin Ahern at Oregon State University on General Biochemistry. For more information about online courses go to ecampus.oregonstate.edu 1. DNA consists of a double helix. Each strand of the helix is a polymer of nucleotides joined together in phosphodiester linkages that have alternating sugar-phosphate-sugar-phosphate links. On the inside of the double helix are the complementary base pairs held together by hydrogen bonds. The arrangement of the double helix is in an ‘anti-parallel’ fashion, meaning that one strand oriented in the 5′ to 3′ direction is directly paired to a complementary strand oriented in the 3′ to 5′ direction. Phosphodiester bonds involve linkage between the 5′ phosphate group of the incoming nucleotide and the 3′ hydroxyl of the previous nucleotide in the chain. 2. DNA contains four bases – A,T,C, and G arranged with A paired with T and G paired with C on the internal portion of the double helix. Hydrogen bonds stabilize these base pairs – two for the AT pair and three for the GC pair. Thus, GC pairs are harder to break than AT pairs. 3. DNA has a major and a minor groove arising from asymmetric glycosidic linkages between the deoxyribose sugar and each base in the double helix. 4. DNA has three major forms – A,B, and Z. The A and B forms are right-handed helices, whereas the Z form is a left-handed helix. The B form of DNA is the most prevalent one and contains about 10.5 bases per turn of the helix. 5. Z-DNA …
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