MBGuru

R/S naming system is based on the Cahn–Ingold–Prelog rules, while the L/D naming system is based on the Fisher projections. These two naming systems are independent of each other. Of all naturally occurring L-amino acids, Cysteine and Selenocysteine are the only ones that are in R configuration, the rest of them are in S.

Draw a line that goes through the furan ring Oxygen atom and splits in half the bond that connects Carbon atoms 3 and 4, that would be the ones closest to you and each one of them is conected to a -OH group. C4-----C3 Now spin the top molecule by 180 degrees and you will get the one on the bottom. But this time C4 will be to your right and C3 to your left.

Strictly speaking the output of Glycolysis is NADH + H+. Why is that? The oxidized form of the NAD cofactor, NAD+, can only accept a hydrogen (H) and an electron in order to be converted in its reduced form NADH. Since a compound loses 2 hydrogen atoms (each atom consisting of a proton and an electron) where does that extra proton (H+) go if it is not accepted by NAD+? It joins the environment, the solution in which the reaction occurs. So a reaction in which a compound is oxidized by an enzyme that uses NAD as cofactor should be written as Compound-H2 + NAD+ -> Compound + NADH + H+ and the reduction reaction should be Compound + NADH + H+ -> Compound-H2 + NAD+ NAD+ is often presented as NAD, while NADH + H+ (or most commonly NADH) as NADH2. For mass relations purposes in that equation the authors had to use NADH2 to show where the second hydrogen for the lactic acid comes from. Yet that equation is still not good, it has to be written as 2C3H4O3 + 2NADH2 --> 2C3H6O3 + 2NAD