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Gene Expression Part 1: Reading Genes to Make Proteins

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Expression of Acetolactate Synthase Enzyme

The gene encoding the enzyme acetolactate synthase (ALS) is essential for organisms that need to make their own supply of the amino acids leucine, isoleucine and valine. The ALS enzyme is needed in the cell to catalyze a reaction in the chemical pathway used to make these three amino acids. There are 20 different amino acids making up the subunits of proteins. All proteins are made from differing combinations of the amino acids (Fig. 6,7) Therefore if you are going to make proteins you need to either make amino acids first or consume amino acids in your diet. Animals consume some of their amino acids (the essential amino acids) but plants and bacteria are able make all their own amino acids.

Fig.6: Amino acids are made from simple atoms and always have an amino end and an acid end Fig.7: Proteins or polypeptides are made by connecting amino acids together Fig: 8. The parts of the gene; the promoter and termination sequences control transcription while the coding region encodes the protein..

The ALS gene is not found in animals but is found in plants and bacteria. The ALS gene consists of several thousand nucleotides of DNA and like all genes has three main parts, the promoter, coding region and termination sequences (Fig. 8, gene sequence abbreviated for demonstration). Each part plays a role in controlling gene expression. The promoter is the on/off switch of the gene, the coding region determines what protein will get made and the termination sequence signals where the gene information ends. Each of these will now be described more fully.


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