hello and welcome to the review of lippincott's biochemistry textbook today we're going to go over chapter seven which is an introduction to carbohydrates if you enjoyed the video please don't forget to give it a like and subscribe to the channel as it helps us out greatly and if you'd like to support the channel you can do so through the patreon link within the description so carbohydrates are the most abundant organic molecules in nature we predominantly think of carbohydrates as our food stuff as it provides a lot of energy for us to be able to do movements but that has other functions as well like a storage form of energy and then also serving as a part of the cell membrane as well now when it comes to classifying the actual structure of a particular carbohydrate there are various ways to do it so for instance there is monosaccharides which just means one simple sugar it is the basic building block of a carbohydrate this can be classified according to the number of carbon atoms it contains so you can see on the side here figure 7.1 you can see if there's three carbons then it's a trios and an example is glyceralderide whereas the glucose which is the most common or the one you always think of as sugars that has six carbons and there's a hexose another way to classify a monosaccharide is by the carbonyl group whether it contains an aldehyde or a keto group so if it's an aldehyde group for the carbonyl group it's an aldos whereas if it's a keto group then it's a ketose now the carbonyl group if you don't know what that is that's basically that one carbon atom that has a double bond to an oxygen so you can see the edhaldehyde group over here we have the functional carbon that has that double bond to the oxygen at the c1 position whereas the keto group this carbonyl group is in the c2 position in these two examples here now disaccharides just means that there's two monosaccharides whereas oligosaccharides means there's three to ten monosaccharides and then when we have more than ten monosaccharides all linked together then that is a polysaccharide and that can be multiple hundreds of sugar units in length so getting to some definitions isomers is a molecule or structure that has the exact same chemical formula but multiple structures so the example of that is fructose glucose mannose galactose these are all isomers of one another because they all contain six carbons 12 hydrogens and six oxygens but yet their structure is all different which obviously gives them different uses now isomers that differ in configuration around only one specific carbon atom is called an epimer and you can see an example of that over here in figure 7.4 where galactose and glucose a c4 epimers of one another because that's where it differs so the one carbon at c4 position is slightly different than the two whereas glucose and mannose are c2 epimers because it's the c2 position carbon which is different and then lastly enantiomers these are just mirror images of one another so this is where you get the l and the d form of a particular molecule so it's the same molecule it's just its mirror image so over here figure 7.5 you can see that we have a glucose on either side but it's just a mirror image of itself so l glucose on the left d glucose on the right d stands for dexter which just means right so the left form and then the right form or d now this is important because enzymes in particular biological processes may only be able to use one of these forms it may either be the l or it may be the d form and we're able to switch them through enzymes called isomerases they're able to interconvert the two types of enantiomers now if that's not confusing enough there's one more way to classify these ones and that's by what's called an enema now this is when the keto group reacts with the hydroxyl group of the same sugar so you create a cyclic form of the sugar and then the carbonyl carbon becomes asymmetric and that asymmetry creates an anima so the example is down here figure 7.6 here we have glucose in the middle now once we create a ring using this carbonyl carbon here so we connect the c1 carbon with the c5 carbon via an oxygen molecule we create these two different types of anomals we've got the beta version and the alpha version as well all you can see is that the main difference is that the oh group is flipped onto the other side so it's not a mirror image of itself it's just another way that you can see this molecule if you show it in the actual ring form over on the b side here over here you can see this is the glucose when it's in its open chain form and sugars is only less than one percent of sugars that actually exist in this open form or this acyclic form once it actually forms the cyclic form then we create an anima so you can see the oh can be on top or on the bottom so whether it's beta or whether it's alpha so then you end up with alpha or beta d glucopyronese remember the d just means it's the right side version of the glucose molecule so it gets a little confusing once you try to take into account all of those different factors but those are what each of those terms mean it's important because the enzymes that actually break these down or utilize these molecules they will specifically only go after let's say just the beta d glucopyrinase here it will only do that one particular type of sugar now a reducing sugar is when that we have a particular type of sugar where it's carbonyl group and its cyclic form is not bound to another sugar via a glycosidic bond a glycosidic bond is just what binds two monosaccharides together so basically this guy right here or all of these cyclic forms they are reducing sugars because our carbon here not at the one position is not in a glycosidic bond so it's able to open and act as a reducing agent so then this is a reducing sugar as soon as this binds for a glycosidic bond to another monosaccharide then it is no longer a reducing sugar so all monosaccharides are going to be reducing sugars because they all are in a single form and then most but not all disaccharides are not going to be reducing sugars the reason why it's not all of them is because our disaccharide doesn't have to form its glycosidic bond at the c1 carbon it may be elsewhere at the c4 carbon let's say and then this guy is still available to be a reducing sugar so when a glycosidic bond is formed it needs an enzyme called glycosyl transferases now when it comes to naming these bonds or these molecules you have to start with the first sugar involved in the bond and start with its anomeric hydroxyl group so just really saying if it's the alpha configuration that's involved in the bond in the bond is an alpha bond if it's the beta configuration then it's a beta bond just to keep it nice and simple there now you can also form glycosidic bonds to non-carbohydrate structures so it can be purine pyrimidine bases aromatic rings which are like steroids bilirubin proteins and then also lipids now if that sugar is attached to an nh2 group then the bond is called an n glycosidic link whereas if the group is bound to an oh group then it's an o glycosidic link and all sugar glycosidic bonds are o type linkages so that's the basics of our carbohydrates next we're going to go into the basics of dietary carbohydrate digestion so the two main sites of carbohydrate digestion occur in the mouth and then the intestinal lumen usually the proximal intestine now it occurs due to glycosidases which hydrolyze these glycosidic bonds the final product being monosaccharides that can then be absorbed into the small intestine now the reason why it only occurs in the mouth and then there's a gap in the stomach and then in the intestine is because the stomach is highly acidic to break down the starting of our proteins so that highly acidic environment actually destroys any amylases or any type of enzyme that's actually going to break down carbohydrates so there's temporarily no breakdown of carbohydrates within the stomach so within the mouth the major dietary polysaccharides are of plant origin being starch and animal origin being glycogen now we're unable to break down the other main polysaccharide and plants called cellulose the animals which are able to break down those are our hindgut fermenters so cows horses etc they are able to actually break down those cellulose within their intestinal tracts whereas people carnivores etc we can't break down that cellulose so we break down starch we break down glycogen and it all starts off in the mouth with salivary alpha amylase which breaks down just those major products into various oligosaccharides it does not break down disaccharides into monosaccharides so it mainly stops at the oligosaccharide level once you've gone through that highly acidic stomach the pancreas then secretes alpha amylase once again which now breaks down those oligosaccharides down into our disaccharides so it releases iso maltese maltese sucrase lactase trilas all of which break down these disaccharides down into monosaccharides so for example sucrase breaks down sucrose into glucose and fructose lactase breaks down lactose into galactose and glucose now those monosaccharides can then get absorbed by the upper jugenum so the starting point of your intestine just after your duodenum but there is slight differences so galactose and glucose gets taken up by active secondary transport meaning that it requires the active transport of sodium ions first and then the energy gathered from that sodium again pumped against its concentration gradient is utilized to bring in glucose and galactose via sglt-1 fructose on the other hand uses an energy and sodium independence transporter called glute5 and then all three of them once they're inside the enterocyte which is the first cell lining within the intestine then transports into the circulation into the portal system via glute 2 another transporter they're not able to just passively diffuse across membranes they need a protein transporter now we can have abnormalities in the degradation of anti-saccharides if we have an abnormality in any of these disaccharide daisies so for instance the most common one is lactose intolerance because after about two years of age it can be natural for you to lose your natural lactase because technically you shouldn't have a demand for milk at that age so then you can no longer break down lactose which comes from milk and then the increased carbohydrate within your large intestine acts as an osmotic agent which then brings water with it so then you have a propensity for diarrhea and then bacteria in your large intestine also ferments it and produces a lot of carbon dioxide and hydrogen gas which is associated with cramps diarrhea and flatulence as well so that's the more common example of an issue with a particular disaccharidase so lactose intolerance occurring in up to 60 percent of adults and then we also have other congenital disorders such as the su-craze iso maltese deficiency which is an autosomal recessive disorder where you can't break down sucrose so then you end up with those same issues and the treatment is just to reduce the amount of sucrose that you eat and enzyme replacement therapy you can diagnose it with oral tolerance tests just giving the sugar so you can how you respond and you can also measure the production of hydrogen gas within your breath so that is the end of this chapter there is a summary portion here feel free to pause it there and then there's also questions on this side as well so pause it there if you'd like to see those questions without the answers and then there's the answers on the right there so feel free to drop a comment i hope you enjoyed this content otherwise we'll see you in the next video