IB Biology Section 3.3 DNA structure

3.3.1 Outline DNA nucleotide structure in terms of sugar (deoxyribose), base and phosphate This is a picture of a DNA nucleotide structure. The green rectangle (nitrogenous base) can be adenine, guanine, thymine or cytosine. The sugar is a 5-carbon monosacharide. This is a picture of a DNA nucleotide structure. The green rectangle (nitrogenous base) can be adenine, guanine, thymine or cytosine. The sugar is a 5-carbon monosacharide.

3.3.2 State the names of the four bases in DNA Adenine Adenine Guanine Guanine Thymine Thymine Cytosine Cytosine Adenine matches with Thymine Adenine matches with Thymine Guanine matches with Cytosine Guanine matches with Cytosine

3.3.3 Outline how DNA nucleotides are linked together by covalent bonds into a single strand The phosphate heads from the nucleotide structure link together using covalent bonds. These form a single strand. The phosphate heads from the nucleotide structure link together using covalent bonds. These form a single strand.

3.3.3 Continued See page 83 diagram © of the Campbell book for the single strand structure of DNA See page 83 diagram © of the Campbell book for the single strand structure of DNA

3.3.4 Explain how a DNA double helix is formed using complementary base pairing and hydrogen bonds. The DNA base is linked to another DNA base through hydrogen bonding. This connects the DNA nucleotides, and gives it the double helix shape. The hydrogen bonds form the “rungs” of the ladder. The sugar and phosphate groups are called the “sides” of the ladder. The DNA base is linked to another DNA base through hydrogen bonding. This connects the DNA nucleotides, and gives it the double helix shape. The hydrogen bonds form the “rungs” of the ladder. The sugar and phosphate groups are called the “sides” of the ladder. Complementary base pairing: Adenine only forms hydrogen bonds with Thymine. Cytosine only forms hydrogen bonds with Guanine. They each have a specific “complementary base” to pair with. Complementary base pairing: Adenine only forms hydrogen bonds with Thymine. Cytosine only forms hydrogen bonds with Guanine. They each have a specific “complementary base” to pair with. Hydrogen bond: A special type of chemical bond that is incredibly strong and hard to break. Hydrogen bond: A special type of chemical bond that is incredibly strong and hard to break.

3.3.4 continued “Cellular DNA molecules have two polynucleotides that spiral around an imaginary axis to form a double helix” (page 82 Campbell Book) “Cellular DNA molecules have two polynucleotides that spiral around an imaginary axis to form a double helix” (page 82 Campbell Book) Also see page 84 of the Campbell book for structure of DNA as a double helix Also see page 84 of the Campbell book for structure of DNA as a double helix

3.3.5 Draw and label a simple diagram of the molecular structure of DNA

Vocabulary List Nucleotide Nucleotide Base Base Covalent bond Covalent bond DNA double helix DNA double helix Complementary base pairing Complementary base pairing Hydrogen bond Hydrogen bond Imaginary axis Imaginary axis Single strand Single strand

For further explanations, see page 18 in the Blue Book