DNA Structure
1 Fig. 5.1.1 below represents a piece of DNA (deoxyribonucleic acid).
a) Colour the sugars, phosphates, adenine, thymine, guanine and cytosine in colours of your choice and
label them.
Use information in your textbook to help you do this.
b) Draw a box around ONE nucleotide and label it
You should have included a base, a sugar and a phosphate.
c) Label a hydrogen bond
Use information in your textbook to help you do this.
2 Write a description of the structure of DNA. Make sure that you use the following key words in your
description.
Hydrogen bonds, complementary base pairing, anti-parallel, pentose sugar, 3` 5`’, sugar-
phosphate ribbon chains, backbone, nitrogen-containing base(s), double helix, purines,
pyrimidines, covalent bonds, polynucleotides, phosphodiester bonds.
DNA is a large molecule. It is a polymer or polynucleotide, made of repeating units, or monomers,
called nucleotides. Each nucleotide consists of a pentose sugar, deoxyribose, a phosphate and a
nitrogen-containing base. The bases are the purines adenine and guanine, and the pyrimidines
cytosine and thymine.
The nucleotides are joined in such a way that the large DNA molecule has two anti-parallel sugar-
phosphate ribbon chains as the backbone. There are phosphodiester bonds, which are covalent bonds,
between the sugar and phosphate groups. One chain runs 3` to 5` and the other runs 5` to 3`.
Slung between these ribbon chains, like rungs if a ladder, are the pairs of bases. A purine (2-ring
structure) always pairs with a pyrimidine(1-ring structure) so that the rungs are of the same width.
These bases pair up according to complementary base-pair ruling, adenine with thymine and guanine
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1 Fig. 5.1.1 below represents a piece of DNA (deoxyribonucleic acid).
a) Colour the sugars, phosphates, adenine, thymine, guanine and cytosine in colours of your choice and
label them.
Use information in your textbook to help you do this.
b) Draw a box around ONE nucleotide and label it
You should have included a base, a sugar and a phosphate.
c) Label a hydrogen bond
Use information in your textbook to help you do this.
2 Write a description of the structure of DNA. Make sure that you use the following key words in your
description.
Hydrogen bonds, complementary base pairing, anti-parallel, pentose sugar, 3` 5`’, sugar-
phosphate ribbon chains, backbone, nitrogen-containing base(s), double helix, purines,
pyrimidines, covalent bonds, polynucleotides, phosphodiester bonds.
DNA is a large molecule. It is a polymer or polynucleotide, made of repeating units, or monomers,
called nucleotides. Each nucleotide consists of a pentose sugar, deoxyribose, a phosphate and a
nitrogen-containing base. The bases are the purines adenine and guanine, and the pyrimidines
cytosine and thymine.
The nucleotides are joined in such a way that the large DNA molecule has two anti-parallel sugar-
phosphate ribbon chains as the backbone. There are phosphodiester bonds, which are covalent bonds,
between the sugar and phosphate groups. One chain runs 3` to 5` and the other runs 5` to 3`.
Slung between these ribbon chains, like rungs if a ladder, are the pairs of bases. A purine (2-ring
structure) always pairs with a pyrimidine(1-ring structure) so that the rungs are of the same width.
These bases pair up according to complementary base-pair ruling, adenine with thymine and guanine
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