in this video I want to talk about the urea cycle so before we actually talk about the urea cycle we have to think about what happens if there's too much nitrogen around well we and other organisms need to get rid of it as simple as that there's too much nitrogen want to get rid of it so how did different animals get rid of nitrogen well some have ammonia and ammonium which they just allows you to diffuse away so fish and amphibians are like that these ammonia and ammonium ions of course water soluble they just diffuse away into the water now we as humans have this thing called urea hence the name for the urea cycle we create this compound here two things that are important about urea that we want to keep in mind are that it's non-toxic and that it's water soluble and we'll talk about why those two points are important in just a second now some reptiles and birds get rid of this product here which is uric acid so this is for reptiles and birds and this uric acid is not water-soluble it's water insoluble but we're not going to focus too much on that or this we want to focus on urea so like I mentioned urea this molecule here is non-toxic and it's water soluble it's non-toxic and that makes sense because this is the way that we're getting rid of our excess nitrogen our excess nitrogen specifically is excess ammonium ion right which is toxic to us so if we can take an a toxic molecule and incorporate it into some other molecule to make it non toxic then we're going to be able to do that that's a good thing so that's essentially what's happening with urea it's also that it's water soluble that makes sense because we have to flow through our blood which is of course mostly water so let's talk about the overview of the urea cycle the purpose of course like I mentioned is to get rid of excess ammonia my are so basically is getting rid of toxic compound which is basically detoxification so this excess ammonium ion travels through the blood to the liver specifically where the urea cycle occurs now this ammonium ion is carried through the blood by glutamate or going to mean with in the form of those amino groups on these compounds so now once it's in the liver the excess ammonium will join carbon dioxide and along with some ACP to make this molecule here which is called carbamoyl phosphate so this carbamoyl phosphate the red portions that I've drawn the amino group here in this carbonyl group come from the ammonium ion and the carbon dioxide respectively and this phosphate cut one comes from the ATP the enzyme that catalyzes this step is called the carbamoyl phosphate synthetase one or cps one and this enzyme is basically regulated in such a way to control the amount of ammonium or excess nitrogen that flows and into the urea cycle after being created after a carbonyl phosphate is created so essentially once I cover on a phosphate is created it goes to the urea cycle and the urea cycle has a bunch of different energy it's a few of which I've drawn here this one here you should recognize as a particular amino acid so the amino group here carboxyl group here and this R R group here this is a spar take this thing here this intermediate you should recognize as an intermediate of another pathway the TCA cycle this thing is called fumarate of course the end product is this urea here so notice I've drawn it some portions right in some portions blue the red portions are to indicate that this this portion this red portion here came from the red portion of carbamoyl phosphate which of course is this ammonium ion here this carbon dioxide this amino group here is blue it's actually the same as this blue amino group here from aspartate so something to keep in mind and I'll talk about the specific reactions of the urea cycle in the next video so how is this urea once it's created in the liver how is it excreted well I wrote here made here so it's obviously gonna start in the liver it's going to go to the blood which is good because urea is water-soluble in the blood is mostly water we mentioned that earlier let's close to the blood it goes to the kidneys because the kidneys are involved in excreting waste products and urine is produced and then urine is what we release or excrete to the outside of our bodies some some urea is also excreted in sweat so you can sweat out urine not urine you sweat out urea I hope that video was a helpful introduction to the urea cycle one last thing I'm a tutor if you live in Southern California feel free to contact me via email at MOOC University at gmail.com for more details check out the description below thanks for watching