When papers or articles say that all proteinogenic amino acids are 'levorotatory' or 'L', they often make a point of saying that only half of them are truly, optically levorotatory. All of them (except glycine) are called 'L' because of their 'opposing' configuration to glyceraldehyde, the original molecule deemed to be dextrorotatory...
Well, all sugars used by living things are supposedly 'R', or so I keep reading....
Are they similar in configuration to glyceraldehyde, or actually dextrorotatory to light?