Deoxyribose 5' & 3' Ends

The building blocks of DNA are individually made up of deoxyribose sugar, a base, and phosphate groups. Position of each carbon on the deoxyribose are numbered 1’ through 5’. The hydroxyl group bound to the 1’ carbon of the sugar, shown as a red sphere linked to a white sphere, is replaced by the DNA base adenine. Then the 5' hydroxyl group is sequentially replaced by three phosphate groups, shown in red and green. Notice that the hydroxyl group at the 3’ end of the sugar remains in place. The final structure shown here is that of dATP, one of four DNA building blocks.

Question 1: What are the components in each building block of DNA?
  1. Deoxyribose sugar, a base, and phosphate group
  2. Glucose sugar, a base, and phosphate group
  3. Deoxyribose sugar, a base, and sulfate group
  4. Glucose sugar, a base, and sulfate group


Answer 1

Answer - (a) Deoxyribose sugar, a base, and phosphate group

Question 2: What are the three groups that replace the 5' hydroxyl group in DNA?
  1. Carboxyl groups
  2. Carbonyl groups
  3. Phosphate groups
  4. Sulfur groups


Answer 2

Answer - (c) Phosphate groups

Question 3: In the example, the hydroxyl group at the 1' carbon of the sugar is replaced by _________.
  1. Thymine
  2. Adenine
  3. Guanine
  4. Cytosine


Answer 3

Answer - (b) Adenine