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I've learnt in chemistry that gaining electrons means reduction, while losing electrons means oxidation. But why is it in Biology textbooks I sometimes come across the term gaining hydrogen??

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  • $\begingroup$ An example would be nice. It's all about context. And they are confusing terms. An oxidizing agent gets reduced when oxidizing something else etc. $\endgroup$
    – AliceD
    Mar 19 '15 at 7:58
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    $\begingroup$ Additionally I think this topic is better suited at chemistry.stackexchange. $\endgroup$
    – Chris
    Mar 19 '15 at 9:04
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    $\begingroup$ No only biology, this notion is there in organic chemistry as well. Remember reduction of alkenes? One of the most common 'reducing agents' used in organic chemistry is LiAlH₄ $\endgroup$
    – WYSIWYG
    Mar 19 '15 at 11:44
  • $\begingroup$ So in a system of two compounds participating in a redox reaction: an oxidizing agent accepts electrons, and thus the oxidizing agent becomes reduced, and the other compound which loses electrons becomes oxidized. A reducing agent donates electrons, itself becomes oxidized, and reduces the other compound. In lots of biological reactions, you can stylize the gain or loss of hydrogen as the gain or loss of an electron, because hydrogen generally donates its sole electron to any given bond. $\endgroup$
    – CKM
    Mar 19 '15 at 22:06
  • $\begingroup$ The definition of electron acceptance and donation came later. Previously oxidation was just addition of oxygen and reduction meant removal of oxygen/addition of hydrogen. $\endgroup$
    – WYSIWYG
    Mar 20 '15 at 11:43
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Hydrogen can accept electrons or donate them, so it can get a bit confusing. For instance, hydrogen donates electrons from a reducing agent. For example, in biology, consider cellular respiration. A co-factor will carry electrons often by reducing an atom with a nitrogen.

Consider NADP+ to NADPH.

enter image description here

The nitrogen atom on the Pyridine group has an oxidation state of +1. When it picks up a hydrogen, to become NADPH, the oxidation state will go to 0 by gaining electrons brought by the hydrogen. Although the hydrogen doesn't bond to the nitrogen directly, it breaks the double bond on the para carbon (The carbon on which the new hydrogen is attached) at the top of the ring, and thus distributes the electrons to the nitrogen.

EDIT - Hydrogen comes from some reducing agent, not a free hydride I'm sure.

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    $\begingroup$ Are you able to annotate the drawing of NADP so that I can follow your explanation better? Thanks :) $\endgroup$
    – Teige
    Mar 19 '15 at 10:33
  • $\begingroup$ I agree with @Teige - a reaction instead of a single molecule would help. $\endgroup$
    – AliceD
    Mar 19 '15 at 12:40
  • $\begingroup$ There is no Hydride-Anion present in any living cell. $\endgroup$
    – Chris
    Mar 19 '15 at 16:38
  • $\begingroup$ Oxidation state and charge are not the same thing. The pyridine in NAD+ is positively charged, but that does not mean that it is +1 oxidation state. $\endgroup$
    – jerepierre
    Mar 19 '15 at 19:57

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