The Chemistry of Life

Topic 3

Starting with a blank piece of paper, draw a diagram of a DNA molecule. One strand has the base sequence of: CTGGAT. Include the details on the parts of the nucleotides (phosphate group and sugars).

3.3 DNA Structure

• Nucleotides are the building blocks of DNA

• Nucleotides are made up of a deoxyribose sugar, a nitrogenous base, and a phosphate.

DNA Bases

• The four bases in DNA are:• Adenine (A)• Thymine (T)• Cytosine (C)• Guanine (G)It is not necessaryto memorize thestructures of these.

DNA Structure

• The DNA nucleotides are linked together by covalent bonds into a single strand. The bonds between the phosphate group and the sugar are covalent. They make up the “backbone” of the DNA’s ladder shape.

DNA Structure

• The double helix shape is formed using complementary base pairing and hydrogen bonds.

• Adenine bonds with Thymine and Cytosine bonds with Guanine.

• Weaker than covalent bonds, hydrogen bonds in the center of the helix. They join the complementary base pairs.

Phosphodiester bond (linkage)

Discovery of the Structure of DNA• Watson and Crick are the two scientists

who were credited with the discovery of the structure of DNA. The didn’t do it alone though…There were two research teams that were competing and working together to discover the structure.

• Watson and Crick used the data of Rosalind Franklin to discover the structure. This data was shared without her consent. To what extent was their discovery dependent on this data?