1. Topic 3.3 DNA Structure
3.3.1. Outline DNA nucleotide structure in terms of sugar (deoxyribose), base and phosphate.
• A DNA nucleotide is composed of deoxyribose, a phosphate group and a nitrogenous base
(adenine, guanine, thymine, or cytosine). The phosphate group is covalently bonded to the carbon
of the deoxyribose, and the nitrogenous base is attached to the deoxyribose on the opposite side.
3.3.2. State the names of the four bases of DNA.
• Adenine
• Guanine
• Thymine
• Cytosine.
3.3.3. Outline how DNA nucleotides are linked together by covalent bonds into a single strand.
• backbone: deoxyribose - phosphate - deoxyribose - phosphate
• nitrogenous base attached to deoxyribose
3.3.4. Explain how a DNA double helix is formed using complimentary base pairing and hydrogen
bonds.
Complementary base paring:
• A = T: adenine forms two hydrogen bonds with its complementary base, thymine
• G = C: guanine forms three hydrogen bonds with its complementary base, cytosine
Hydrogen bonds:
• the combination of hydrogen bonds between A = T and G = C hold the two strands of DNA
together
• each strand forms a helix, the two strands together form a double helix
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2. 3.3.5. Draw and label a simple diagram of the molecular structure of DNA.
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