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What Ae Heterocyclic Amines?

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Heterocyclic amines (HCAs) haves been known to cause colon cancer in animals and people. In a study done at Oregon State University, Stephanie Smith-Roe identified a gene that can keep people from being particularly vulnerable to these chemicals.HCAs are compounds that are formed when amino acids and creatine react at high temperatures, as often occurs in overcooked meat. There are at least 17 different HCAs, some of the most common being PhIP, IQ, and MelQx. Expose to HCAs can cause mutations in a cell?s DNA since they bind to the bases in DNA and make mismatches more likely. PhIP, for example, often attached to guanine, making it likely to mistakenly pair with adenine, thymine, or another guanine instead of cytosine.DNA is always at risk for errors to occur, so the body has ways to repair damage to the DNA or to kill damaged cells. One method is mismatch repair: DNA mismatch repair proteins recognize when a mismatch has occurred, and they remove the segment of the newly created stand of DNA containing the mismatch. Nicks occur in the strands of DNA being synthesized and they allow the proteins to recognize which strand to remove. DNA polymerase and ligase then create a new strand of DNA in place of the one removed.Smith-Roe found that the genes that code for these repair proteins are MLH1 and MSH2. Many people are born with a faulty copy of one of these genes, or one becomes turned off by an unknown process called hypermethylation. Often, this isn?t a problem because they have one good copy of the gene, but this one can also become disabled over time.When performing experiments on mice without the MLH1 gene, Smith-Roe found that they were four times as likely to develop precancerous lesions in their colons when exposed to HCAs as those with the functional genes. They also had three times as many permanent mismatches in their DNA, and their bodies didn't send the usual signal to kill the damaged cells (apoptosis). While the coupling of guanine to thymine or another guanine was often repaired, the mismatch-repair system often failed to correct guanine-adenine pairings.Luckily, for those lacking the gene, there are ways to limit HCA consumption. Since HCAs form at high temperatures, cooking meat for prolonged periods at these temperatures increases HCA formation. Adding starch or acidic marinades to the meat has been shown to limit HCA formation as well.

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