LECTURE 09 From DNA to Protein

LECTURE 09 From DNA to Protein - 2:010 Principles of...

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2:010 Principles of Biology Lecture 9 From DNA to Protein Two lectures ago we covered the evidence that DNA is the genetic material. It contains the information necessary to determine the physical characteristics of the organism. One main piece of evidence is the observation that when pieces of DNA are taken up by a cell it could change the characteristics of the cell. This process is called transformation and we saw that it occurs in bacteria. We will later see that it also can occur in eukaryotic cells. These segments of DNA contain units of information that determine the characteristics of the cell and the organism. These units are called genes . One of the major questions in biology was What do these genes do? How do they determine phenotype (expressed, observed characteristics) of a cell or organism? We also previously said tht the most abundant macromolecules in the cell are proteins. They do all the tasks required by the cell to keep it alive and functioning. They catalyze chemical reactions, control the chemical composition of the inside of the cell and provide structure. Proteins directly determine the characteristics of the cell. Therefore, there must be some relationship between the DNA genetic material and the proteins present in the cell. In the early 1900’s Archibald Garrod, a British physician, provided the first clues to answer this question. He observed that certain human diseases ran in families and therefore, were inherited. Therefore, some change in the gene, representing a malfunction of the gene led to the disease. He hypothesized that disease symptoms arise from the inability to make a particular enzyme. He was particularly interested in a disease called alkaptonuria, which is like arthritis but in which the urine turns black. This is the result of the secretion of high levels of a chemical which is normally present at very low levels. He hypothesized that there is normally an enzyme that catalyzes a reaction involving this molecule (alkapton = homogenistic acid). Malfunction of this enzyme enables alkapton to accumulate to dangerously high levels producing the symptoms of the disease. 1
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This proposal was based on Garrod’s knowledge of metabolism, which is the sum of all of the chemical reactions occurring inside the cell. Metabolism involves the synthesis ( anabolism ) and the breakdown ( catabolism ) of all organic molecules inside the cell. These usually occur in a series of steps where the product of one reaction is the substrate of the next. The Red X is the malfunctioning enzyme and E is alkapton.
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