In this video, we're going to begin talking in more detail about monosaccharides. Recall from our previous lesson videos, we already mentioned that monosaccharides are individual carbohydrate monomers, and that makes them the simplest form of sugar. Now, sugars have names that generally end with the suffix -ose. So, really, anything that ends with -ose, the likelihood is that it's going to be a sugar. For example, glucose ends with the suffix -ose, and so glucose is a sugar. Now, monosaccharides can actually be grouped in several different ways. Moving forward through our lesson, we're going to talk about all of the different ways that monosaccharides can be grouped. I'll see you guys in our next lesson video when we talk about how monosaccharides can be grouped either as aldoses or ketoses. I'll see you guys there.
Monosaccharides - Online Tutor, Practice Problems & Exam Prep
Monosaccharides
Video transcript
Monosaccharides
Video transcript
So monosaccharides can be classified into 2 groups based on the nature of their carbonyl group, and those two groups are either an aldose or a ketose. Now notice that both aldose and ketose end with the suffix -ose, so we know that these are sugars. And, again, these two categories of sugars are going to be classifying the monosaccharides based on their carbonyl groups. And so an aldose is going to be a sugar whose carbonyl group is an aldehyde. And recall that aldehydes can be abbreviated with CHO. And then, of course, a ketose is going to be a sugar whose carbonyl group is a ketone.
And so if we take a look down below at our image over here on the left-hand side, we're showing you the difference between an aldehyde and a ketone group. And so recall that aldehydes have the H here in them, and so that reminds us that they're going to be carbonyl groups that are attached to a hydrogen. And so they're going to be found at the end of a molecule. And then, of course, ketones don't have that H in them, and so they're going to be attached to another R group. So they're going to be found in the middle of a molecule.
And so, if we take a look at our images over here of our monosaccharides, we can see this one over here on the left is Glyceraldehyde and notice that even in its name it tells us that it has an aldehyde group. And so, what we can say is that glyceraldehyde is an aldose. And then if we take a look at this sugar over here, notice it is Dihydroxyacetone and this one has its carbonyl group right in the middle. So it has 2 R groups going either way. And so that makes this sugar right here a ketose. And so we can classify all of our monosaccharides either as aldoses or as ketoses based on again the nature of the carbonyl group. So that concludes this introduction to aldoses and ketoses and we'll be able to get practice as we move along through our course.
Monosaccharides
Video transcript
Alright. So now that we already know from our last lesson video that monosaccharides can be grouped based on the nature of their carbonyl groups, either as aldoses or ketoses. In this video, we're going to talk about how monosaccharides can also be grouped based on the number of their carbon atoms. And so, monosaccharides that have 3, 4, 5, and 6 carbons are respectively called trioses, tetroses, pentoses, and hexoses. And so these prefixes here are revealing the number of carbon atoms that these monosaccharides have. Now, these highlighted prefixes can also be preceded by the prefixes "aldo" or "keto" to respectively indicate an aldose or a ketose. And so if we take a look down below at our image, we can classify the following monosaccharides based on both the number of the carbon atoms that they have and based on the nature of their carbonyl groups. And so if we look at this first sugar over here, we can see that it has a total of 1, 2, 3 carbon atoms and this is going to make it a triose, "tri" meaning 3. This sugar right here has 4 carbons. So, this is going to be a tetrose. This one here has 5. So, it's going to be a pentose. This one has 6. It's going to be a hexose and this one over here has 7 carbon atoms making this a heptose. And so really these are the prefixes that I would suggest committing to memory to indicate the number of carbon atoms that the monosaccharides have. Now, as we mentioned up above, we can also attach the prefixes "aldo" to indicate that all of these sugars that are bracketed here are going to be aldoses since they have the CH2O aldehyde group. And then of course, this sugar over here is going to be a ketose because notice that it's going to have, a carbonyl group that is not at the end. Instead, it's going to be in the middle here and it has 2 R groups branching off. And so, technically, we can call all of these sugars aldotrioses, aldotetroses, aldopentoses, or aldohexoses. And then, of course, this sugar over here is going to be a ketoheptose. And so, now that we can understand how to group monosaccharides based on both the number of the carbon atoms and the number of their carbonyl groups, we can get some practice applying these concepts in our next few videos. So, I'll see you guys there.
Select the appropriate label for each of the three following monosaccharides:
Problem Transcript
Monosaccharides
Video transcript
Alright. So now that we've already learned how to group monosaccharides based on the nature of their carbonyl groups, and based on the number of carbon atoms that they have, in this video, we're going to move on to how to assign numbers to all of those carbon atoms of linear monosaccharides. And so later in our course, we'll focus on cyclic monosaccharides. But in this video, we're focused on linear monosaccharides. And so, the carbon atoms in linear monosaccharides are numbered based on the positioning of the carbonyl group. Or in other words, they're numbered based on the positioning of the aldehyde or ketone group. And so the key is that the carbonyl carbon atom, that's part of either the aldehyde or ketone should always be assigned the lowest possible number. And that way, we can designate the numbered carbon atoms as C1 for the first carbon, C2 for the second one, C3 for the third carbon, and so on. And so in our example, we're going to appropriately number the carbon atoms in each of the following 3 linear monosaccharides, starting with glucose over here on the far left. And again, the key to assigning numbers to the carbon atoms of linear monosaccharides is right here in this second line. And that is that we want the aldehyde or ketone to be assigned the lowest possible number. And so, when we take a look at glucose's structure, we can see that it has an aldehyde group. And that is the CH2O and it's up at the top. So, we want this carbon atom right here to be assigned the lowest possible number when we're trying to assign numbers to all of the carbon atoms. And so, of course, that means that this carbon is gonna be number 1 and all of the other carbon atoms that go down are sequentially going to be carbon 2, carbon 3, carbon 4, carbon 5, and carbon 6. And so this is the appropriate numbering of the carbon atoms in the glucose molecule. So let's move on to mannose over here, and again, we can see that it has an aldehyde group here at the top just like glucose. And so we want the carbon atom of this aldehyde group to be the lowest possible number. So we're gonna give it a one again and then again, we're going to assign each of the atoms going down sequentially as carbons 2, 3, 4, carbon 5, and carbon 6. So the numbering is very similar to the carbon numbering of glucose. So then, of course, we can move on to our last but not least monosaccharide over here, and we're just gonna number these carbon atoms from bottom to top just like we did for the previous 2. Right? No. Not right. So remember that the key to assigning numbers to the carbon atoms of linear monosaccharides is that we have to identify the aldehyde or ketone and then assign the lowest possible number. And so we can see that the fructose molecule on this page has its ketone group towards the bottom of the Fischer projection. And so if we were to number the carbon atoms from top to bottom, like what we did with both mannose and with glucose, then notice that the ketone carbon atom is assigned carbon number 5. However, if we number the carbon atoms from the bottom towards the top, then notice that the ketone carbon atom would be assigned carbon number 2. And of course, 2 is lower than 5 and 2 would be the lowest possible number. And so that means that we're not going to be numbering the carbon atoms from top to bottom on this fructose molecule. Instead, we're gonna be numbering from the bottom to the top. And so the carbon numbering that you see here is the correct carbon numbering for this fructose molecule on this page. And so, again, the main takeaway here is that when we are assigning numbers to the carbon atoms of linear monosaccharides, we want to look for the aldehyde or ketone and make sure that the carbon atom is assigned the lowest possible number. And so we'll be able to get some practice applying the concepts that we've learned in this video in our next practice video. So I'll see you guys there.
Number the carbon atoms in the following linear form of fructose below: