Chem181- Topic6, 2 .docx - DR JOE SCHWARCZ Any discussion of agriculture these days really has to make reference to genetically modified foods A lot of

Chem181- Topic6, 2 .docx - DR JOE SCHWARCZ Any discussion...

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DR. JOE SCHWARCZ: Any discussion of agriculture these days really has to make reference to genetically modified foods. A lot of interesting potential in that area, but there's also no question that the very concept of genetic modification breeds fear in a lot of people. And much of that is due to a lack of understanding of what this technology is really all about. The truth is that we have been genetically modifying food since time immemorial. We'll go back to this Assyrian relief-- dates back to 870 BC. What we're seeing here is artificial pollination of a date palm with some pollen taken from another palm. And if you consider the grapefruit, one of our favorites, well, that's just a hybrid of oranges and pomelo. And that was a consequence of probably accidental cross pollination. And triticale which is commonly used these days for all kinds of baked goods, it's a hybrid of wheat and rye. All caused by cross pollination. And then modern science entered the picture and it became possible to take seeds of a plant and expose them, for example, to some sort of chemical or some radiation to cause mutations in the seed. That is, changes in the DNA, hoping that it would lead to some beneficial trait. Well, that was, of course, a very laborious process and the hope was that accidentally you would arrive at some genetics that were an improvement over any existing varieties. And, certainly, there were some good discoveries made in that area. However, today we can be very specific about the kind of genes that are introduced thanks to a technique called gene splicing. Genes are just fragments of DNA that code for specific proteins. And it's possible to take one of those little pieces of DNA and snip it out and introduce it into the DNA of another organism. And this is referred to as recombinant DNA technology. Basically, what we're doing is instilling a set of instructions because DNA tells the organism what sort of proteins to manufacture. Let's look at an example. Chymosin. That's an enzyme. Enzymes, of course, are just protein molecules, and chymosin is used in the making of cheese. You take milk, chymosin is added, the milk curdles, it separates into the curds and the whey, and you filter off the whey and you get the curds lef behind, and that's cheese. Well, traditionally, chymosin came from the stomach of calves. An extract of the stomach is known as rennet, and when that is added to milk, it curdles the milk and you get cheese.
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Scientists, however, have discovered the particular gene that is used to form chymosin. And it is possible to extract that from the cells of calves-- so we get the DNA of the calf-- and the specific fragment of the DNA that codes for chymosin has been separated. It can be put into a yeast cell, and then the yeast cell will churn out chymosin.
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