3.1.1 From genetic information to protein function

Almost every process in a cell requires proteins. As you saw previously, antibiotics often exert their bactericidal and bacteriostatic effects by binding to proteins that are crucial to the structure or function of the bacterial cell.

The function of a protein is largely determined by its structure. Proteins are composed of building blocks called amino acids. The sequence of these amino acids determines the structure of a protein. The amino acid sequence of a protein is specified by the DNA sequence of a gene (Figure 19). So, there is a direct relationship between DNA and the structure and function of a protein.

Figure 19 The DNA sequence of a gene encodes the sequence of amino acids in a protein.

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This figure is a schematic diagram showing three genes 1, 2 and 3, at different locations within the genome. Each gene is expressed (via transcription and translation) as a chain of amino acids in a specific sequence – chains 1, 2 and 3 respectively. Each amino acid chain then folds up into a particular three-dimensional structure, determined by its amino acid sequence.

Figure 19 The DNA sequence of a gene encodes the sequence of amino acids in a protein.

In 1958, Francis Crick, who helped discover the structure of DNA, proposed an explanation regarding how genetic information, encoded in DNA, can be converted into a functional product, a protein. In the first phase, a strand of DNA is used as a template to produce a complementary strand of RNA (ribonucleic acid). This process is called transcription. The RNA strand is then translated into a sequence of amino acids to form a new protein.