when we break down amino acids inside our liver we essentially remove that Alpha amino group and what we have left over is a carbon skeleton so in this lecture and the next several lectures what I'd like to focus on is the fate of that carbon skeleton so when we metabolize amino acids and we form that carbon skeleton by removing that Alpha amino group what exactly happens to that carbon skeleton so all the carbon skeletons that we form when we metabolize the 20 different types of amino acids inside our liver cells all those carbon skeletons lead to one of seven different molecules and all these seven molecules are intermediates of the metabolic pathway the metabolic system that allows us to generate high energy ATP molecules so let's recall some basic facts about metabolic path way so let's begin with the citric acid cycle so this is our citric acid cycle and inside our liver the point of the citric acid cycle is to help us generate oxaloacetate why because oxaloacetate is ultimately the starting material to produce glucose via glucogenesis as it takes place inside our Li cell so if we can form any one of these intermediate molecules that can ultimately help us form oxaloacetate and that can lead to glucose production now inside our liver we can actually use pyruvate to basically form oxaloacetate and this pathway is catalyzed by the enzyme pyruvate carboxylase and so what that means is we can use pyruvate to actually help us generate glucose because if we transform pyruvate to oxaloacetate we can then use this in glucogenesis to help us form glucose now what about this pathway here so if we take pyruvate the second fate of pyruvate is to undergo decarbox so the enzyme pyua decarboxylase transforms pyruvate into acetal coenzyme a now what happens to ACL coenzyme a well we can use acetyl coenzyme a to help us generate fatty acids but we can also use acetyl coenzyme a to help us generate Ketone bodies so by transforming acetyl coenzyme a to aceto ACL coenzyme a this ultimately can be transformed into Ketone bodies now one fact that you have to remember is acety coenzyme a cannot be used at least inside humans to actually generate glucose molecules and what that means is even though it seems like we can can use AAL coenzyme a transform it into citric acid cycle ultimately form oxaloacetate and then form glucose via glucogenesis that is not actually true and the reason is the following when we use acetal coenzyme a and we feed it into the citric acid cycle we actually use up a single oxaloacetate so we use a single oxyacetate combined with acet coenzyme a and we form citrate and so ultimately even though we do form oxaloacetate at the end we use up one oxaloacetate at the beginning and the net result is zero so what that means is we cannot use ail coenzyme a to help us form glucose in our liver now let's focus on all these different amino acids so basically if we metabolize an amino acid and the car Caron skeleton of that amino acid is used to form any one of these intermediates here or pyruvate these are known as glucogenic so glucogenic amino acids are those amino acids that when metabolized help us form intermediates that ultimately lead to the production of glucose so that includes all these these these these and these so for example let's take tryptophan tryptophan if it follows a specific pathway that will ultimately lead to the production of pyruvate now pyruvate basically goes this way via the pyruvate carboxilate enzyme that forms oxaloacetate and that then helps us form glucose via glucon neogenesis now if we look at aspartate for example aspartate can be transformed into oxaloacetate and we add actually looked at this example in in a previous lecture and then the oxyacetate goes on to form glucose via glucogenesis so all of these amino acids are known as glucogenic now if we look at these these and these ultimately helps us form these two molecules and so these can then be used to form Ketone bodies so these are known as ketogenic so all of these are ketogenic now the only ones that are solely strictly ketogenic are actually Lucine and lysine why well because tryptophan if it follows one pathway we can form acetyl coenzyme a in which case it's ketogenic in a different pathway it can form aceto ACL coenzyme a again it's ketogenic but in this pathway it helps us form p pate and pyruvate goes this way to help us form glucose now we can also go this way of course and this will be ketogenic but if we look strictly on this pathway this pathway is gluc glucogenic so tryptophan is both glucogenic and ketogenic so the only ones which are only ketogenic are Lucine and lysine this is the list of all the glucogenic only we have 14 and this is the list of both ketogenic and glucogenic so as we saw earlier we have tryptophan but we also have isoline phenol alanine and tyrosine so uh my suggestion if you're going to memorize these memorize these two and these four but don't memorize this because if you memorize these two you know the other 14 which essentially must be glucogenic only now one caveat however is the way have listed is I have 14 glucogenic and four under both sometimes you're going to see three anine listed under both so that means we have 13 here not including three anine and five here including three anine and that's simply because of the way you define glucogenic so if you define glucogenic one way the three ends up being here if you define a different way the 3en ends up being here now now that's really not too important what's important here is to notice that the majority of the amino acids that are metabolized inside our liver actually end up being metabolized into glucose because 14 or in some cases 13 essentially end up being transformed into glucose and then that glucose can be used to help our cells generate high energy ATP molecules so in the next several lectures we're basically going to look at the actual Pathways that lead to all these different intermediates when we actually metabolize the 20 amino acids