 So, now after this talking about this carbohydrate protein, let's talk a little bit about nucleic acid. So, we all know this nucleic acid, somehow it's connected through this kind of double helical bundle, okay. And what we know that this kind of bonding generally can be found in DNA and then the DNA is storing our information which actually opens up during the information passing phenomena, transcription and translation and all those things it transfer its information to mRNA, which also having some chirality and this mRNA actually interacts with the ribosome and that actually creates the protein molecules that we actually require. So, this whole process how the DNA interacts with RNA, it interacts with the ribosome and over there how the protein molecules are actually synthesized, this full system is known as the central dogma of biology. So, that is how the information is passes on. Now, think about that because we are chemists, we are not biologists, so we want to understand like, wait a while, how it is actually happening there. So is the DNA going to open up and interact with the mRNA all the time or it opens up at particular certain conditions? The answer is it opens up only at a particular condition, just wait a minute, sorry about the background noise, so this DNA molecule actually senses some changes in the environment of the biology and only when it actually opens up. So, those kind of phenomena which actually adds to the opening of the DNA, sometime that in generally known as the transcription factors and what are those transcription factors? They can be physical conditions like temperature, like someone actually having some wrong metabolism, the body is heating up, it actually sensed by the DNA and they actually try to stop it by creating some protein molecules which might going to help you out. It might be pH, it might be the oxygen concentration, it might be the carbon dioxide concentration and so on and so forth. So, this can be physical in nature and they can be chemical in nature. pH, I would say it is probably chemical in nature because it is actually nothing but sensing the proton concentration of the solution because all our, for example, cellular system is generally tried to be near neutral condition 6.5 to 7.5, but sometime if the cell is having some malfunctionality, for example, cancerous cells, they actually become very much acidic in nature, it can go even close to 3 or 4, so at that time the biology senses is and try to respond to it. So, how this biological response happen, the DNA somehow detects it or other co-factors somehow detects it and that detection is also coming through a molecular recognition. So, that means this transcription factor, how it is interacting with this DNA, it is actually nothing but a molecular recognition in certain cases. And over here, again the chiral nature of the DNA and chiral nature of that particular chemical can be very crucial for ensuring that we are actually responding to the correct call, not any false alarms. So, that is why the molecular recognition, even the DNA and RNA are very important. And additionally what is recently has been found that DNA and RNA are not only acting as the simple gene information transfer agents, they can also act as an enzyme. So, for an example, there are certain numbers of systems known as RNA enzymes or sometime it is also known as ribozymes, so you can take a look into that. So, these are very crucial and they actually play a huge role during the gene splicing. So, sometime the genes has to be restored, has to be modified during the evolution and whatever the things happening with the gene and the structure and its conservation or its modification, even some of the RNAs are playing a huge role on controlling like which particular portion of the DNA or RNA I have to cut it out, which particular group I have to look into. Even over there, it is going through a molecular recognition and again the chiral nature of the RNA molecules which is a very important factor. So, recently it is found it is not only the RNA, but the DNAs even which is known as a very robust material, it is found that DNA can also even participate in catalysis or some chemical reaction in certain cases. So, those are also known as DNA enzymes. So, what they do? They sometimes also do the similar work like the cleave or functionalize. For an example, you need to put a phosphate group in one particular portion so that it can recognize a particular molecule as a transcription factor. So, for that you have to functionalize the DNA or RNA segment with the phosphate group and this DNA does this reaction through an acid based reaction. So, this kind of and cleave a particular DNA at a certain place so that it can respond to a particular condition. So, those kind of things and even sometime repairing of the DNAs or RNAs. So, those kind of things are happening over there. And again for these particular interactions you have to do that at particular certain conditions. You cannot miss even by one base pair and during that how the molecules is certain that this is the thing I have to follow. The DNA and RNA not only use their own chirality, but also the change of the chirality on the backbone of the nucleic acid they are actually reacting on and both this chirality plays a huge role to find out exactly what is happening and how it can be controlled. So, that is why molecular recognition is a huge important factor and biology interacts through the molecular recognition. So, it is not only the protein not only the carbohydrate even the RNAs and DNAs have a huge role to play. And now you look into that one step back and take a look into that. We have protein in biology. We have carbohydrate in biology. We have DNAs and RNAs in biology and all of them use chirality as one of their very important tool to do the molecular recognition. And this molecular recognition is very important not only for their metabolism, but also you can say that is how the biology is interacting with the surrounding atmosphere, right? So biology we found it is having a chiral environment. So now, as Rishabh has earlier told us today that if you do a reaction with a chiral environment because biology it is doing its reaction with an enzyme, carbohydrate, protein, DNA, RNA, that environment is chiral and if it does a reaction over there, you are going to see a difference of their chiral preference. You are actually going to see a enantiomeric excess. So in biology if you throw a set of enantiomers in the same concentration or same equivalent, if the biology interacts with them, they are not going to interact with the same, with the same rate, with the same extent of the reaction. That will be different. And at the end, you will say one enantiomer is reacting more than the other. So you are going to create enantiomeric excess. So that means it is not only that I have to create synthetically a chiral environment, but if I allow the biology to interact with something, I am expected to see some enantiomeric excess. Everybody agrees to this particular point or not? If anybody has any question, please let me know because this is a very crucial point. That biology is chiral and that is why when it is going to interact with a set of chiral molecules, it is going to distinguish between them. It is going to create an enantiomeric excess. So with that thing in mind, we are going to go to the next system. And this particular system that the biology can detect chirality and uses chirality and can invoke enantiomeric excess, keep that thought in mind, we will come back to this point just before we conclude today's class. Now with all those things in mind, I am going to define only the amino acids today. The carbohydrates and RNAs and DNS, we will discuss later parts. The carbohydrate probably we are not going to discuss, DNA RNA we are going to discuss a little bit later point. So amino acids, all the natural amino acids, which is also you can say it is alpha amino acids because over here you have a carbon, you have a carboxylic acid, you have a R group, you have an amine group and you have a hydrogen. So these are the common structure of all the alpha amino acids found in the biology naturally. So over here, first we will try to understand this alpha amino acids we found, how we can find out whether it is a L amino acid or a D amino acid. This is alpha, Greek term and this is capital L, how to differentiate that. So for that you have to just remember the simple rule called corn. So what is corn rule? So over here what you have to do is simply put the carbon, draw it into a telegeometry, put the hydrogen on the back, that is the first thing, hydrogen on the back that means it should take the back most position, the weight spot. Then put the groups, carboxylic acid group, R group, NH2 group and then follow the corn, the corn stand for carboxylic acid, then R, then the amine group, just find out exactly how these groups are oriented and put it 1, 2, 3. So over here this is 1, this is 2, this is 3. Hydrogen on the back and then orient carboxylic acid, R group and NH2 group as 1, 2, 3. This is not exactly the CIP rule, this rule defined much earlier than the CIP rules, so it is a little bit qualitative in nature. Over there this carboxylic acid, COR in group you just find out and see how they are connected. So put 1, 2, 3 and see how they are connected. So over there you can see they are connected anticlockwise. So if they are connected anticlockwise that will be an A-lamine acid. And the same system, say carboxylic acid, hydrogen and now say I exchange the R with NH2. So now find the corn, carboxylic acid at the top, R over here, C over here. So now connect there in the clockwise. If it is clockwise it is going to be a D-amin acid, okay? So that is you figure it out, L-amin acid and D-amin acid. So in the exam if I ask you the question like draw this L-amin acid, if I ask you to draw the structure you have to ensure that you have drawn that in the particular orientation. Because this L and D is actually showing their spatial orientation, specific spatial or three dimensional orientation and it has to be correct. It has to follow this simple corn rule. Put the hydrogen on the back, carboxylic R and NH2 group such a way that they can be connected in the anticlockwise then it is L. If it is connected in the clockwise it is D, fine? Now most of the amino acid found in biology, majority of them are L-amin acids. So very rarely you see or you counter a D-amin acid. We will come into that later when the D-amin acid can be found. So it is mostly found in L-amin acid and the D-an L-amin acid can be interconvert among themselves. We will come into that later typically via hydrolysis. Okay, so now what we are going to cover? There are 20 naturally occurring amino acid. So I am going to draw the structure, general structure of it. I will put out their name and how they actually expressed with three letter and one letter code. Because this will be important in the later part of the class. So over there I am going to say this particular code that means you have to understand which particular amino acid I am talking about. So for that what I am going to do over here is the following. I am going to draw the structure, general structure of the L-amin acid. So the rest of the thing will be same, what will be the changing thing will be the R group. So over there I am going to write the structure of the R group, the name of the amino acid, the three letter code and the one letter code. So they are actually explained in either of the way. So the first set of the system I am going to talk about are known as the aliphatic amino acid. That means the R group is typically an aliphatic group. So the first example of that is when R is equal to nothing but a hydrogen. So now you can imagine if I put a hydrogen in the place of R that is not going to be a chiral molecule anymore. Because it is going to have a sigma plane going through that carboxylic acid group carbon and NH2P. So that is the only a chiral amino acid. And the name of this amino acid is glycine. Three letter word gly, one letter word G. So that means if I want to give you an example like this will be a protein group and over there this is a GGG chain. That means you have to understand I am saying there will be glycine, glycine, glycine connected to it. The second one is the next one you can think about put a methyl group over there in the place of R. The rest of them are same. This is known as alanine. Three letter code ALA, one letter code A. The next one comes an isopropyl. The name of this is valine. Three letter word VAL, one letter word V. Then the chain actually extends a bit and extra CH2 group added over here. This is known as leucine. Three letter word LEU, one letter word L. And then there is a another amino acid which is nothing but very similar to the structure but an isomer of that. So what happens over there one of the CH3 ships over here and then it is CH2 CH3. So you can say one of the CH3 over here ships down and this is isomer. So it is known as isoleucine. So in the name it is saying that is isomer of leucine. Three letter word ILE, one letter word I. So these are the five different amino acids can be found in biology which is having simple aliphatic groups in its structure as an R group. Next, again I am just drawing the group I am drawing and over here I am mostly following this R group. So again I am going to write the name over here. So the structure over here first, then the name of the amino acid, the three letter code and the one letter code. So after aliphatic we look into aromatic groups. That means there is an aromatic group present over there. The simple one we found it is a CH2 and then a phenyl group because putting a phenyl group very close to will be a little bit tricky. So biology finds out that let us put a CH2 spacer in between them and you can say that this is nothing but alanine derivative where alanine was CH3 but instead of one hydrogen I am putting a phenyl group. So that is why the name comes phenyl alanine, three letter word PHE, one letter word F because it pronouns with like F pronunciation, F phonetics. Why does not PHE it will come into that just when we will be completing this part. Then comes this particular CH2 group then this particular heterodermatic system which is nothing but an indole group present over here and the name of this is tryptophan, three letter word TRP, one letter word W. Again why not T will come into that very soon. The next one is come a phenol group. The name of this is tyrosine, three letter word TYR, one letter word Y. So these are the three different aromatic compounds we can have over here. Then comes some of the polar systems. So one of the beginning ones comes CH2OH. So these are the structure of this R group over here I am drawing CH2OH. If alcohol group the name is serine, three letter word SER, one letter code S. Then comes a variation of it where it forms a secondary alcohol. First it was a primary alcohol, then it is a secondary alcohol, OH group comes a little bit closer. The name of that is 309, three letter word THR and that is where the one letter word T was used. So that is where tryptophan or tyrosine does not get their one letter code with T. They have to be happy with Y and W respectively. So these are the two different polar groups we can have. And additionally we can have two other compounds which are can be the amide bonds CH2 and then an amide bond. And this name is asparagine, three letter code ASN, one letter code N. And then there will be another variation of it where instead of one carbon there are two carbon in between and then we have the amide bond. And the name of the system is glutamine and the three letter code is GLN, one letter code is Q. So with this we complete the aromatic and polar set of the molecules. Then we actually move towards the acidic set of the molecule. And over here again it should draw the structure. So in the acidic group is nothing but the same amide bonds we have drawn earlier, their acidic group. Instead of amide put an acid group and that will be the system so I am going to have. So it will be CH2CWH which is known as aspartic acid, three letter form ASB and it is carboxylate form it is known as aspartate. One letter code D because A is already been taken and then this extra C is to connecting between them. It is known as the glutamic acid or known as the glutamate in its carboxylate form, three letter of GLU, one letter word E. So these are the two different acidic group you can have. Then comes the basic groups. Over there you can have the interesting structures, four CH2 chains and then a primary amine group. There is a long chain and then you are having a primary amine this is known as lysine, three letter word level S and one letter code K and then you can have another one from the same basic group it is known as arginine where you have the three CH2 groups and then you have over here a guanidine group over here and this particular set is known as arginine, three letter word ARG, one letter word R and then the another one we have in the basic format which you can also consider in the aromatic format but you put it in the basic format because it mostly plays its role in the basic system where you have a imidazole group over here. So this is nothing but a imidazole group. The name of the system is actually histidine laminate acid HIS and H. So these are all the acidic and basic groups falls into the natural amino acids and we have only a few of them left. I am going to draw them structure and three letter one letter. So for that we are going to have other two molecules which are actually having we put it as a special group but you can also consider it in the polar group which actually has thiol groups present CH2SH the name of the system is cysteine, C letter word C by ES, one letter word C and then you can have another version of thiol but not exactly thiol but a thiol ether and this is known as methionine, MET, one letter M and then there is another version which is very rarely found but it is having very important factor present in the terms of enzymatic activity. It is a selenium version of the cysteine instead of sulfur you have a selenium and the name is selenocysteine C letter word ACC, one letter word U and with all them considering almost all of them and one important amino acid which is very important and a little bit different structure present is this one where it is actually a secondary amine completes a circle because it is more like a completes a circle complete make a cycle out of it. So it is a two degree amine present instead of one degree amine commonly present and the name of this amino acid is proline, C letter word PRO, one letter word P and this is very important to develop the turns into the protein structure because generally amino acids when they form they form in a linear fashion but if you want to create a turn you put proline over there and due to the background the structure of this proline backbone you automatically create a turn. So that is why creating a turn in the protein structure especially say on these regions so prolines are actually been used over there. So these are the different amino acid structures. So today we learn mostly about the molecular recognition how it is important and we found that biology use molecular recognition a lot and they use chirality as one of their tool and we also know about the different amino acid structures. Those will be very much important for your exams and assignments. So with that we will stop over here the next class we will start off from there and then you find out some interesting facts that how the biology interacting with this chirality can affect and can be used even as a sign of life in the real world. So that we will discuss later so we will stop it over here if anybody has an equation please go ahead and I am stopping recording.