Back when I was in school, I was told that aspartame is a so-called “left-handed” sugar; that is, it’s built as a mirror-image of ordinary sugars, and that’s why our bodies don’t process it. All our enzymes (or whatever they are, I’m a little fuzzy here) are right-handed, built to handle right-handed proteins and sugars, etc., which is what all the foods we eat make. If this isn’t correct, please enlighten me!
Anyway, my question is about left-handed sugars and bacteria. Are there bacteria in our ordinary environment that can consume left-handed sugars, or are they all right-handed too? And therefore, does diet soda cause cavities and tooth decay in the same way that regular soda does? It seems to me that if there are only right-handed bacteria living in my mouth, then they wouldn’t chew holes in my diet-soda covered teeth (though obviously the acid would still effect the enamel).
I really do brush my teeth and don’t drink a lot of soda; this is a hypothetical question and I’m not trying to find a way to avoid brushing.
Well, your school done you wrong. Aspartame is not “left-hand sugar”. It’s made from two common amino acids. It is broken down in the body into aspartic acid, methanol, and phenylalanine. And small amounts of formic acid and formaldehyde.
Dang! Stupid school. And here I thought that was one of the few pieces of useful information I’d retained from there. I’m telling you, the older I get the worse I realize my pre-college education was, it’s very depressing.
Are you sure you’re not misremembering what you were taught? As QtM said, aspartame is not a sugar at all, but fructose (also known as levulose) is a “left-handed sugar”. (It’s the mirror image of dextrose.)
AFAIK it still contributes to tooth decay, though.
Fructose is not the mirror image of glucose. Glucose is an aldose (most highly oxidized carbon in position 1), Fructose a ketose (most highly oxydized carbon in position 2)
You have the right idea, but backwards - all of our proteogenic amino acids are “left-handed” (levorotary, or L) and all of our common sugars (if not all of the sugars) are “right-handed” (dextrorotary, or D). The human body is set up only to process the correct-handed molecules.
Also, as others have pointed out, aspartame is made up of amino acids (L-amino acids, in fact), not sugars, but the same idea applies - if you could make the enantiomer (mirror image) of sucrose (sugar), it would have a different (maybe better, maybe worse) sweetness as well as different metabolism.
Bacteria in general are much more versatile than humans. Many bacteria can process D-amino acids (the “unnatural” one), and as a matter of fact, penicillin and vancomycin antibiotics rely on the fact that D-alanine is essential for bacterial cell walls.
L-sugars are a lot harder to deal with. Why? Because sugars have 3-4 different chiral (handed) centers, while amino acids only have 1-2. Bacteria make D-alanine by taking L-alanine and inverting its single chiral center - they’d need 3-4 equivalent enzymes to convert a L-sugar to a D-sugar.
Yes, but not for any of the reasons listed above. Diet sodas cause cavities because they actually do have calories - but because artificial sweeteners are more potent than sugar (aspartame is 180x as sweet as sugar), there’s very little material for bacteria to grow on. You’ll still have bacteria food all over your teeth (remember aspartame is made up of L-amino acids, which everyone can process), but just 180x less. Chances are the phosphoric acid is worse for your teeth than the sugary stuff at that point. Or maybe your own spit.
Yes, you’re quite right of course. (Organic chem was a few years ago!)
Sucrose is made up of dextrose (glucose) and levulose (fructose), right? And dextrose rotates polarised light to the right while levulose to the left, hence the names.
I was confusing it with L-glucose. That’s the stereo isomer of D-glucose (dextrose), and it was considered as a low-calorie sweetener, because it’s not metabolised in the same way (link). But I don’t think it’s used commercially. I do wonder, though, if the OP was thinking of L-glucose.
