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Current time:0:00Total duration:9:46

Video transcript

this video we're going look at the biological redox reactions of alcohols and phenols over here on the Left we have the ethanol molecule so this is a our two carbon alcohol the carbon that we're most concerned with is this carbon right here which has one bond to this oxygen atom and in the liver ethanol is oxidized to ethanal so over here on the right is the ethanol molecule a two carbon aldehyde and once again we're concerned with that carbon in yellow and so one easy way to tell that ethanol was oxidized to ethanal is to see that on the Left we have one bond of that carbon to oxygen and over here on the right we now have two bonds of that carbon to oxygen so an increase in the number of bonds to oxygen is oxidation you could also assign oxidation states to this carbon and you will see that there's an increase in the oxidation state of that carbon and then you could also think about electrons right so Leo the Lion goes ger loss of electrons is oxidation gain of electrons is reduction and so if I think about these electrons here in magenta you can see that those electrons are lost from the ethanol molecule so loss of electrons is oxidation ethanol is oxidized if ethanol is oxidized something else must be reduced that's how redox reactions work and what's reduced is nad plus over here on the left so this is nad Plus which stands for nicotinamide adenine dinucleotide the adenine is hiding in this R portion and we have a nitrogenous base ring with an amide functional group over here on the right for the nicotinamide portion of the molecule plus one formal charge on this nitrogen gives us nad plus so this is nicotinamide adenine dinucleotide nad plus and since ethanol is oxidized nad plus must be reduced so reduction means gaining of electrons and so nad plus is going to gain those electrons in magenta from ethanol so if we think about a possible mechanism if I took these electrons between the oxygen the hydrogen and move them in here that would form our double bond between the carbon and the oxygen but there many bonds to to this carbon right here so the electrons in magenta are going to move to this carbon down here on NAD+ to this carbon that would push these electrons over here and now I'd push these electrons here off onto the nitrogen so if we if we showed what happened with the movement of all of those electrons right over here on the right this carbon right here at the top already had a hydrogen bonded to it right and it gained another hydrogen with two electrons the two electrons were the ones in magenta right here so this this hydrogen right here is this hydrogen and the electrons magenta move over there to our ring and then we would also have right pi electrons moved over here and then we had a lone pair of electrons move off onto the nitrogen like that and then we still had some PI electrons over here on the right and so this molecule is called n a d H right so it's gained it's gaining the equivalent of a hydride right it hydrogen with two electrons and so we can see that nad plus gains two electrons and gains of gaining electrons is reduction so nad plus is reduced to NADH since nad plus is is reduced it allows ethanol to be oxidized and so we would refer to nad plus as an oxidizing agent right it is the oxidizing agent for ethanol even though it itself is being reduced so that's something that confuses some general chemistry students sometimes all right so now over here we have the NADH molecule and this this reaction is catalyzed by an enzyme and the enzyme is alcohol dehydrogenase okay so this is the catalyzed by the alcohol dehydrogenase enzyme like that and this reaction is reversible so if we think about the reverse reaction right we think about ethanol being reduced to ethanol and so if ethanol is reduced to ethanol NADH would be oxidized to nad plus and so let's think about a mechanism where we could oxidize NADH and reduce the ethanol if I took this lone pair of electrons in the nitrogen and move it back in here alright that would push these electrons off over here and now the electrons in magenta on this on this bond right here would attack this carbon right here so the electrons in magenta right we could think about the electrons in magenta right as being right here and you can think about that as being a hydride right so a hydrogen with two electrons giving it a negative 1 formal charge and even though we sweep saw and we've seen in some earlier videos that hydride isn't necessarily the best nucleophile you can think about this as being a nucleophilic attack if it makes it easier for you because this carbon right here would be partially this carbon right up here would be partially positive and right so the negatively charged electrons would attack that carbon and in doing so that would push these pi electrons off to then to then grab this proton here and that would give you your ethanol molecule and that would convert NADH back into an ad plus so you could think about NADH right as being oxidized it is losing it is losing two electrons right the electrons in magenta loss of electrons is oxidation and since NADH is the agent for the reduction of ethanol to ethanol you would say that NADH would be the reducing agent for this example and the best way to remember that NADH is the reducing agent is it is the one that has the hydrogen on it so it has the hydride which is capable of being the agent for the reduction so therefore NADH is the reducing agent this NAD+ NADH conversion and vice versa is extremely important in biochemistry this happens in numerous biochemical reactions and so it's important to understand what's happening with those electrons on these molecules let's look at another biochemical example of redox and here we have on the Left phenol alright so this is our phenol molecule and once again we're most concerned about this carbon the ones that's attached to this oxygen and there are many ways to oxidize phenols and so oxidized phenol like like the Jones reagent with sodium dichromate sulfuric acid and water would be I would be capable of oxidizing phenol to this molecule over here on the right which we call benzoquinone right so this is this right here is a benzoquinone molecule and just real fast you could see that you know this carbon right now has two bonds of carbon to oxygen of carbon to oxygen so it has been oxidized so phenol can be oxidized to benzoquinone using numerous organic reagents once you make benzoquinone you could reduce that to this molecule over here on the right which is called hydroquinone so there are there are several again organic reagents that can reduce benzoquinone to hydroquinone hydroquinone let me change that spelling there and then from hydroquinone right you could oxidize hydroquinone back to benzoquinone pretty easily and so once again in organic chemistry there are lots of reagents that can do these these redox conversions and in the body you're usually talking about the NAD+ NADH system alright so so we've just studied that and if we look here at this molecule you can see it's a it's a quinone right so so you can see the benzoquinone portion of this molecule and this is called ubiquinone you be referring to the fact that this is ubiquitous this compound is found in everywhere it's found in all the cells in nature and the other name for this would be coenzyme q and so this is this is a very important part of the electron transport chain and if we look at you beacon own going to this molecule over here on the right you can see this is uh this is like a hydroquinone analog here so this is you be quinol and so this these carbons right are being reduced right from this from this chemical reaction that I've drawn here so ubiquinone is being reduced to you be quinol and so if you equidome is being reduced something else must be oxidized all right so the NADH is being oxidized to n d-plus and so the nadh right it's the one that has this this hydride on here which can serve as the reducing agent so here NADH is acting as the reducing agent the agent for the reduction of ubiquinone to the ubiquinol molecule over here on the right and so this is this is just an oversimplification of part of the electron transport chain alright where you're transporting electrons which eventually leads to oxidative phosphorylation and also ATP synthesis which of course gives us gives us energy and so this isn't meant to be an exhaustive detail of those biochemical processes but it's just to show you how you can analyze biochemistry using using a simple knowledge of organic chemistry and the importance of NAD+ and NADH in biological systems