Free Chemistry NEET Video Lectures for Biomolecules

00:00:25 P Singh from uh department of chemistry IT Delhi. I'm going to discuss about the uh biomolelecules. In this unit uh we are going to uh talk about different kind of biomolecules such as carbohydrates, proteins and uh nucleic acid. We are going to uh classify carbohydrates, protein, nucleic acid and vitamins based on their uh structures. And uh we are going to uh learn about uh uh differences between the uh DNA and RNA. Um these are the nucleic acid. And we are also uh going to appreciate the role

00:01:12 of biomolelecules in uh in the uh system. So uh first let's talk about the biomolelecules. Biomolecules are uh organic compound found in living system. found in living system. are we can say that living systems are uh built up of various complex uh biomolecules such as carbohydrates, proteins, nucleic acid lipids etc. Particularly carbohydrates and proteins are essential constituent of our food. essential constituent of our food and their interaction. Their interaction constitute logic of life processes.

00:03:16 Carbohydrates serve as a major source of metabolic energy. major source of metabolic energy. Now, so before discussing about carbohydrates, uh let's talk about that you know what are carbohydrates chemically? What is the question here? What are carbohydrates? Carbohydrates are usually defined as polyhydroxy poly hydroxy alihides alihides are ketones. Polyhydroxyldihides are ketones are the compounds that yield after the hydraysis polyhydroxyldihide aret. So again I would like to uh rephrase it

00:04:39 the definition of carbohydrate. Carbohydrates are usually defined as polyhydroxy alihides or ketones are the compound after hydraysis generates polyhydroxy alihides and ketones. The chemical structure of carbohydrates are commonly represented by fisser projection fer projection formula. Here I will show you two examples of carbohydrates. uh first one is glucose and the second one is fructose. Both these glucose and fructose have the molecular formula C6 H12 06 consistent with the journal formula

00:06:06 C6 H2O 6 That made early chemists think that basically carbohydrates are hydrates of carbon. Hydrates of carbon. Now let's look over the you know these structures fisser projection dlucose and uh you know um d fructose. So here I'm going to draw the fisser projection structure of dlucose. Here you can see that this molecule has uh four kyal center. and it has alihide in its framework. This is fer projection formula of dlucose. Now I will draw fer projection formula of d fructose. This is D

00:07:46 fructose. If you look over these two compounds, one is dlucose is um polyhydroxy alihide and uh d fructose is polyhydroxy ketone. Now I will talk about the classification of carbohydrates. Classification of carbohydrates. The term carbohydrates or saccharide or sugar are interchangeably used and saccharide comes from our early language. Uh if you look over uh in Sanskrit uh it is known as circara. Circara in Sanskrit and Seron in Greek, Saccharon in Greek and Sakaram in Latin. So term carbohydrates or saccharides are

00:09:31 sugars which are used interchangeably has been derived from our ancient languages. As I mentioned that in Sanskrit it is known as circara. In Greek it is known as saccharon and in Latin it is known as saccharum. We can classify it into uh two part. First one is simple carbohydrates. Simple carbohydrates. Simple carbohydrates are monosaccharides. Simple carbohydrates are uh monosaccharide and they can be also called as single sugar. single sugar. Second one is complex carbohydrate. Complex carbohydrates

00:10:58 contain two or more monosaccharide. contain two are more monosaccharide monosaccharides which are linked together. Now these complex carbohydrates uh can be further subdivided into three parts. First one is disaccharides. Disaccharides which contain two monosaccharide contains two monosaccharides. Second one is oligosaccharide. Oligosaccharide contains 3 to 10 monosaccharides. 3 to 10 monosaccharide monosaccharides. And the last one is polyaccharide. Polysaccharide which contains more than 10 more than 10 uh monosaccharide

00:12:57 units. So here we uh subdivided complex carbohydrates based on the number of monosaccharides in three subdivision disaccharide, oligosaccharide and polyaccharide. Disaccarides contains two monosaccharides. Aligosaccharide contains 3 to 10 monosaccharides and polyaccharide contains more than 10 monosaccharides which are linked uh with each other. To make you understand in a better way, I would like to write here a schematic representation where various monosaccharides are linked with each other and this

00:13:55 is getting hydrayed. After the hydraysis it will generate many monosaccharide units. Here in this polyaccharide M is a monosaccharide unit. Monosaccharide unit. It's a subunit I can say and here after the hydrarolysis it generates number of monosaccharides. This molecule is polyaccharide. So a polyaccharide where number of monosaccharide subunits are linked with each other is getting hydrayed and that generates that many number of monosaccharide after the hydraysis. Now I would like to classify

00:15:13 monosaccharides that what are monosaccharides? Let's talk about classification of monosaccharides. classification of monossaccharide. It can be classified in two way based on the number of carbon atom present in the molecule. Carbon atoms present in the molecule. Second, whether they contain an alihide or keto group. So two things we have to remember regarding the classification of monosaccharides. It can be classified based on the number of carbon atoms in the molecule. And the second thing that

00:16:38 it has an alihide r keto group. These are the two factors. Thus say a let's let's take example thus a monosaccharide containing three carbon atom with three carbon atom. is called as trios. Trios tri stand for three and O is stand for the sugar. Three carbon atoms trios. If it has four carbon atom, one molecule contains four carbon atom. Then it is called tetros. Please remember tet stands for the four O's stand for the sugar. If it has three carbon atoms then trios. If it has four carbon atom tro and if it

00:17:56 has five carbon atom then it is called pentos. Similarly it can go to hexos heeptos etc. Now a monossaccharide containing an alihide group, an alihide group is called LDOS. Alihide group is called LDOS. Whereas a monosaccharide containing a keto group is called ketos. Now it is it is clear that we have classified monosaccharide based on two criteria. If a monosaccharide is having three carbon atoms then it is called trios. If a monosaccharide is having four carbon atoms then it is called tetros.

00:19:28 Similarly five carbon atom then pentos and six and seven then hexos and heeptos etc. The another criteria is based on the functional group. If it has alihide functional group in its framework then it is called ldos. Whereas if it has uh ketone in its functional group u in its framework then it is called ketos. These two classification are frequently combined. A C4 L Eldos for example is called Eldot Tetros. LDO stand for the LDH. Eldo tetros. Eldot tetros. Similarly, a C5 ketos is called keto pentos.

00:20:49 Now I will show you few examples of these LDOS and ketos to make you understand in a better way. So let's take you know structure of an LDOS as I mentioned LDOS will have an alihide group and according to definition it will also have polyhydroxy framework. So to represent it I am making this structure. This is an LDOS. For ketos we need to have an a ketone group and polyhydroxy framework which I am denoting by this uh structure. This is a Now I will take an specific example such as an Eldo tetros.

00:22:05 In eldotros as I mentioned it will have an alihide group as well as it will have four carbon numbers because while discussing the classification of u monosaccharide we were focusing on two things. one is the number of carbon atoms and uh the other thing is the type of functional group does it has alihide or uh ketone. So here I am taking example of um eldotros. So eldo means it has alihide and tetros means uh it has four carbon atom. So and eldo tetros it has C4. Similarly I will take from ketos group

00:23:16 keto pentos ketos ketoentos uh means that it has like ketone in its framework and polyhydroxy C framework and since it is ketoentos it has like you know five carbon atoms 1 2 3 4 5. So this is a ketoentos ketoentos it's C5. Now we will take some practice problem uh that you know uh uh how many kyality centers are there in uh eldotros and in ketoentos. So let's take a look on the structure of eldetros. If you look over in the case of L2 tetros we have two chyal center one and two. Similarly in the case of a

00:24:39 ketoentos it has two chyal center one and two. Another problem we can think that how many stereo isomers are possible for these two monosaccharide for eldotros and for ketoentos. So as we know that it depends on the number of kyal center and uh um since it has like two kyal center. So four stereoisomers for both the molecules are possible. Now I will talk about DL designation of monosaccharide. DL designation of monosaccharide. The simplest monosaccharide are the glyceraldihide and uh dihydroxy stone. The simplest

00:26:08 uh monosaccharides are um com compounds glyceraldihide and di hydroxy acetone. Let me draw the structure of glyceraldihide and uh dihy dihydroxy acetone. Glyceraldihide has one chyal center and one alihide group in its scaffold. Whereas dihydroxyacetone has two hydroxile group and one ketone group. in its scaffold and based on the nomenclature we can tell them basically glyceraldihide is an eldotrios. Why it is eldrios? because it has alihide group and it has three carbon in its scaffold. And this dihydroxy stone is

00:27:38 a keto trios. Now because of the three carbon atoms and similar way ketone group we have named it ketotrios. Of these two compounds only glyceraldihide contains a kyality center. You can see here only glyceraldihide has one chyal center whereas dihydroxyacetone does not have uh any chyal center. Therefore, glyceraldihide exist in the uh ensumer farms and that are known to be uh I mean based on their absolute configuration uh r glyceraldihide and s glyceraldihide uh I will uh discuss in you know detail uh first I would like to

00:28:29 write their structure. So based on the absolute configuration the two glycerald deihides are possible because it has one kyal center. Uh first one is where the alihide group it attached to the carbon and hydroxile group and hydrogen. So this is the carbon which is a chyal with which you can see here one alihide group and CH2O is attached and one hydroxil and hydrogen is attached. This is plus glyceraldihide. Another example is We are. Now this is minus glyceraldihide. In plus glyceraldihide what is important

00:30:06 here that hydroxil is right side whereas in the minus glyceraldihide hydroxile is at the left side. This this is the you know basic difference between the plus and minus glyceraldihide for absolute configuration. I would like to remind you that you know um tan in gold pre-log u convention generally plus glyceraldihide plus glyceraldihide is known as R plus glyceraldihide. Whereas minus glyceraldihide is S minus glyceraldihide. Now this nomenclature is based on the you know absolute configuration and

00:31:27 before this nomenclature came in practice which is based on the absolute configuration. There was a another system which was introduced in 1906. in 1906 by MA Rosen of Ma Rosen of which is known as DL system. DL system. In DL system, plus glyceraldi dihide is known as uh D plus glyceraldihide is known as uh D plus glyceraldihide. Whereas minus glyceraldihide is known as L minus glyceraldihide. These two compounds moreover serve as configurational standards for the uh rest of the sugar molecules or you can

00:33:01 say that um for the monosaccharide. A monossaccharide which highest kyality center is having uh some configuration similar to the D plus glyceraldihide is known as the D sugar or if it has the um configuration similar to the L glyceraldihide then it is known as um L sugar. Now I will um explain it with the example. uh these two um so one who whose highest number kyalty center has the same configuration as the you know d it is called the duger d glyceraldihide with the d glyceraldihide and is called the duger one uh with the

00:34:03 uh having absolute configurence similar to the l glyceraldihide is called L sugar. Let me write here the uh structure of these two sugars. So first I will write the structure of u eldos uh a d eldo pentos as I mentioned that eldos so it it has to have eldhide in its scaffold and Now you see that it has highest kyality center. This is the highest kality center. So 1 2 3 4. Four is the 1 2 3 4. Four is four the highest kyalty center and this is five. This is a dldo pentos a d eldopentos. Another example of

00:35:32 ketos is an L ketohexos. Here again since it is ketoexos it has to have ketone group in its scaffold. And finally the carbon the last you know kyalty center containing carbon. Now here these two these are the highest numbered kyalty center. Sorry. Highest numbered kyalty center highest numbered kyalty center. Now let's compare it with the d glyceraldihide and l glyceraldihide. If you look over in the case of dlyceraldihide, it has resemblance with the deglyceraldihide that highest numbered kyalty center. So that's why it

00:37:19 is called d eldopentos. Whereas in the ketos case it is similar to L glyceraldihide. Hence it is called L keto hexos. L ketohexos. Now I would like to discuss some of the practice problem. classify the following monosaccharides. Here I'm writing some monosaccharide and based on the their absolute configuration based on their you know uh configuration of uh highest numbered kyalty center you have to uh classify them. So let me draw the fer projection formula of this example. This is one. Another one is

00:38:43 having the ketone group. So if we name it without the configuration we can say that it this first example is having like you know 1 2 3 4 5 carbon. So it becomes eldopentos and alihide group. So it becomes eldo pentos. The second example has 1 2 3 4 5 6 7 carbon atoms. So it becomes and ketone group in its scaffold. So it becomes ketos. And the third example which I want to introduce is eldo eldhexos. Now since we have to classify these monosaccharides uh based on the DL uh you know designation let's look over the

00:40:34 structure uh and look over the highest numbered kyality center in all these cases. Let's take first example. In this example, the highest numbered kyalty center has configuration similar to the dig glycerald deihide. So it becomes d. Then in second example again it has configuration similar to the d glycerald deihide. So it becomes d. And similarly in the third also it has configuration similar to the D glycerald deihide. So it becomes D. Now I will give you some more example to uh classify the uh

00:41:27 monosaccharide based on the uh their um you know uh configuration of highest uh numbered kyalty center. uh indicate whether each of the following these glycerald deihides are D or L glyceraldihides. Let me take the practice problem of uh glyceraldihide and we will identify that it has DRL uh configuration. So here I'm drawing the glyceraldihide. Now we need to identify that it is D or L glyceraldihide. Uh you would have learned in your studio class that one interchange of the substituent on a symmetric carbon atom

00:42:36 leads to the enansomer whereas the two interchange of the substituent leads to the same molecule. So here what I'm going to do that uh before comparing with the DRL glyceraldihide I will do two interchange. First interchange will lead to hydroxile group left hand side and second interchange will lead to exchange between the hydrogen and hydroxythyl group. Now let's compare it with uh d glyceraldihide dlyceraldihide and uh l glyceraldihide. Now I'm bringing again back that you know the

00:43:52 highest membered kyalty center when it is similar to the D then it is called uh D glyceraldihide and when it is similar to the L glyceraldihide then it is called uh L U sugar. Here in this case it is similar to the L as hydroxil is in left side. So it becomes L uh glyceraldihide. Now I will take another example again. we will do that two interchange because two interchange will give the similar uh compound. So let me first write it in the three-dimensional form. Now the first interchange will take place between the hydroxil and

00:45:24 CH2O group. Sorry, first interchange will take place between the hydrogen and uh alihide group. So and the second interchange will take place between the hydrogen and uh hydroxythyl group. So it becomes hydroxil here and hydrogen and then now let's compare it with the D and al glyceraldihide since hydroxil group in this part is left hand side. So it becomes L glycerelihide. Now I would like to talk about the configuration of LDOSes. Lot tetros have two asymmetric center. Therefore, four stereo isomers are

00:47:10 possible. Whereas eldopentos has three stereo centers. Hence u you know um eight isomers are possible whereas the eldhexos has four stereo centers. Hence 16 is true isomers are possible. So all these uh dependent the these uh is true isomers are possible based on the number of kyal centers available in the scaffolds. Uh I will like to stop here and in the next class I'm going to talk about the you know possible uh eldohhexoses possible eldopentosis and possible eldotrosis. Thank you very much.