Free Biology NEET Video Lectures for Molecular Basis Of Inheritance

00:00:39 [Music] I am Py Pradeshi PGT B Techchnology Kendra Vidal number three Delhi and today I'm going to make you learn about structure of DNA and the function of DNA. In this session, you will learn how the DNA has been synthesized, what are the different components of the DNA, how those components are being bonded with each other and what is the function of the DNA. So as we know DNA is blueprint of life. What is the meaning of blueprint? Blueprint means whatever the cell has to perform their function, whatever the cell has to

00:01:42 perform their activity that is under the control of the DNA. That means DNA directs the cell when the cell have to divide when the cells have to go undergo reproduction and other activities. That's why DNA is called the blueprint of life. Let's know something about the journey of the DNA. Today we know about the DNA because of the contribution of some of the scientist. Let us know some of some of them. The first of all the DNA was observed by a great scientist in 1868 Frederick Viser in the WBC cells of

00:02:30 pus and he named this compound as nucle. Later on Vin Chargef in 1950 gave the ratio which is also called Chargef ratio which states that in a particular DNA fragment number of purine will always be equal to number of parimedine. If suppose there are thousands adden nucleotide in a particular DNA fragment then there will be thousand thymine in that DNA. Similarly, the concentration of guanine will always be equal to concentration of cytosine in a particular DNA fragment. After this, Rosalyn Franklin

00:03:16 and Morris Wilkins gave the first picture of DNA with the help of X-ray crystalraphy. With the help of that, Watson and Crick determined the structure of DNA. And then finally Watson and Creek in 19 sorry uh 1953 discovered the structure of DNA what we learned today as double helical structure. Now what are the chemical composition of DNA? What are the different chemicals which form the DNA? We will see in the next coming slide. DNA is considered as biomolelecule. Why it is considered as biomolelecule? Because biomolelecules

00:04:04 are present in cells and control the different function of the cells. Like that DNA is also present in the cells and control various activities of the cells. DNA synthesize a protein and protein function various types of activities. DNA is composed of nucleotides. Various types of nucleotides combines together to form the DNA. That's why nucleotide is the monomeic unit of DNA. Now what are nucleotides? Nucleotides consist of three major components. One is sugar that is carbohydrate. Second one is nitrogenous

00:04:50 base. Third one is phosphate molecule. These three major components combines together to form one nucleotide and many of the nucleotides combines to form nucleic acid that may be DNA or RNA. Sugar and nitrogenous base combines together to form nucleotide and nucleotide combined with phosphate to form nucleotide. And I and I as told you many of the nucleotides combine to form nucleic nucleic acid which may be DNA or RNA. Now let's see which sugar makes the nucleotide or we can say makes the DNA.

00:05:40 There is deoxyibbos sugar as well as ribos sugar which constitutes the nucleic acid. As we know nucleic acid is of two type DNA and RNA. DNA stands for deoxyboubboucleic acid and RNA stands for ribboucleic acid. DNA is having deoxyibbos sugar while RNA is having ribos sugar. What is the major difference between these two sugar? Ribbo sugar and deoxyibbos sugar. If you can see in the picture ribos sugar is having five carbon that's why ribos sugar is considered as pento sugar. Here are the carbons. Carbon number one 2 3 four and

00:06:30 five. And this one is deoxyibbos sugar. It is also having five carbon that is it is a pento sugar. The major difference in between these two sugar ribos and deoxyibbos sugar is at the second number of carbon. In ribos sugar there is hydroxile group O group while in deoxyibbos sugar at second number of carbon there is deficiency of one oxygen molecule only hydrogen is there. That's why this is known as deoxy. It means deficiency of oxygen at the second number of carbon. And this is the major difference between

00:07:08 ribos sugar and deoxyibbos sugar. And deoxyibbos sugar is present in DNA. This is one of the major difference between DNA and RNA. If you can see this sugars are found in cyclic structure. What is the reason behind this? Why the carbohydrate molecule found in cyclic form? And the answer is formation of hemi acetyl and hemiital. Whenever the alcohol and alihide or alcohol and ketone combines together they form their respective compound which is called hemi acetyl or hemiital. This reaction is very much

00:07:51 simple. You can understand over here. The hydrogen of alcohol this hydrogen will transfer at the oxygen of carbonial carbon and it will form O. Similarly the fourth valency of this carbon will be satisfied by the remaining part of the alcohol that is R- O and this form the hemi acetyl. The same reaction will be here with the alcohol and ketone. The hydrogen of alcohol will transfer over the oxygen. It will form O. And the remaining part of the alcohol will combine with the carbon and complete its fourth valency

00:08:31 and make the hemical. The same reaction is occurring in the carbohydrate also. This O group will participate in the reaction. The hydrogen will transfer over the oxygen of the carbon and it will it will make O group and remaining part of this carbon will form a ring with this carbon number one and because of this hemi acetyl formation the carbohydrates are found in cyclic structure. This again you will learn in the biomolelecule chapter of class 11th. Next major component of DNA is nitrogenous bases. There are five types

00:09:10 of nitrogenous bases cytosine, thymine, uricil, guanine and ananinine. Commonly they have been classified into two categories pyramidine and purine. Pyramidine includes cytosine, thymine, uricil and purine includes guanine and adenine. Out of these five nitrogenous bases only four are present in the DNA and four are present in the RNA. Cytosin, thymine, guanine and adenine are present in DNA. Cytosin, uricil, guanine and adenine are present in RNA. The third major component of the DNA is phosphate molecule.

00:10:00 When we talk about DNA, there is just one phosphate in the DNA, this phosphate. But when the nucleotides combines together, when the nucleotides combines to form the DNA, while forming the DNA, while synthesizing the DNA, the three phosphate molecules are there in the nucleotides. But while making the bond, two of this phosphate will remove from the this triphosphate. And because of the breaking of the bond, whatever energies are being released out, that energy is utilized to make phosphodiester bond.

00:10:35 With the help of that energy, the one phosphate molecule will combine with the sugar molecule of the nucleic acid. Now let's see how these major components of the DNA or RNA combines together and what are the different bonds. First we will see how the sugar molecule combined with the nitrogenous bases. This is the deoxyibbos sugar which is present in the DNA. At the first number of carbon this nitrogenous base it may be adenine, cytosin, thymine or guanine. Urasil is not there in the DNA. So this nitrogenous base having NH

00:11:21 group over here. The the hydrogen of this NH group will bond with the O of the first number of carbon of the sugar. They will form the water molecule and the water molecule will released out from there and the remaining part of the nitrogenous base will attach over the first number of carbon to form the nucleotides. So combination of sugar molecule and nitrogenous base is called nucleotide and the bond which combine this together is n glycosidetic linkage. There are four types of nucleotides respectively in DNA as well

00:12:04 as in RNA. In RNA we have adinosine, we have guanosine, we have cytoine and uradine. Similarly in DNA we have two deoxyadinosine, we have two deoxy guanidine, we have two deoxytodine and thyidine. So these are the four types of nucleotides which further combine with the phosphate molecule to form the nucleotide. Here you can see how the nucleotides combine with the phosphate molecule to form nucleotide. This you already know. Okay, this sugar plus with the nitrogenous pair. This is the nucleide and this nucleotide will

00:12:50 combine with the phosphoric acid. Here you can see the hydrogen of the phosphoric acid and the alcohol of the fifth number of carbon they will interact with each other and they will form the water molecule. The water molecule will released out and the remaining phosphoric part will combine at the fifth number of carbon to form one nucleotide and this bond is called phosphoester bond. It is called phosphoester bond because whenever acid and alcohol reacts with each other they form esester and here

00:13:26 the acid is phosphoric acid which is reacting with the alcohol that's why this bond in between the phosphate and the sugar is called phosphodiester bond. Let's see how the nucleotide combined with the phosphate molecule. Here you can see this is the sugar molecule combined with the nitrogenous base to form one nucleotide and this phosphate molecule will interact with the alcohol of the fifth number of carbon. The hydrogen of phosphate molecule and the alcohol part of the sugar molecule they interact with

00:14:03 each other. they will form water molecule and the water will release out and the the remaining part of the phosphate will combine over the fifth number of carbon and they will form one nucleotide. So there are four types of nucleotides respectively in DNA as well as in RNA. In DNA there are datps, dctps, dttpps and dgtps. Like that in RNA there are ATP, CTP, UTP and GTP. So these nucleotides combines together to form DNA as well as RNA. These nucleotides combines to form DNA and these nucleotides combines to form

00:14:56 RNA. Now how two nucleotides combines together to form the polynucleotide chain. Here you can see this is one of the nucleotide molecule. This is the another DNA nucleotide molecule. The phosphate molecule of the second number of nucleotides will participate in the bond with the third number of carbon of the first nucleotide. Both this hydroxil molecule will interact with each other. They will form water and they the remaining part will combines together and this bond is called phosphodiester bond

00:15:40 because two alcohol is participating with one acid and they are forming phosphodiester bond. like that this third number of O is free for the bond formation and this ducleotide is having two terminals one is five terminal and another is three terminal that's why either it is DNA or RNA they have five prime end and three prime end because of the sugar molecule This is how the nitrogenous bases combines together. Adinine always combine with the thymine and vice versa. Thymine will combine always with adenine. Like that

00:16:35 guanine always combine with cytosine and cytosin always combine with the guanine. If we talk about DNA because DNA is double helical structure. They have two strands. So these two end strands combines together with the help of these bonds and this bond is called hydrogen bond. In case of adinine and thymine there are two hydrogen bond and in case of guanine guanine and cytosine there are three hydrogen bond and these two these hydrogen bonds helps the two strand of the DNA to combine together to

00:17:12 form two strands of the DNA. This is how the two strands of the DNA are being combined with the help of hydrogen bond. So there is hydrogen bond in between the two strands of the DNA or we can say in between the nitrogenous bases of the DNA. Now let's see some of the features of the model given by Watson and Creek. The first point related to this model is DNA is double standard helix. DNA has two chains twisted around each other on a common axis which is right-handed helix. You can see in the picture the

00:18:04 DNA is double stranded one this strand and other is this this strand which are twisted with each other. Second point of this model is be though both these two strands have polarity. Polarity means they have five prime end and three prime end. Both these two strands have this five prime end and three prime end. Next feature of this model is both the strands are antiparallel. Antipar means one strand will be in five prime to three prime and another strand will be in three prime to five prime end.

00:18:45 Both the strands cannot have the same ends. That means if one end is having five end in one strand the another strand there will not be five strand there will be three prime end. So both the strands are antiparallel in nature and both the strands move in 5 to 3 or 3 to 5 direction. The two chains are not identical but complimentary to each other. That means these two strands these two strands are not identical but both the strands are complimentary. Complimentary means if adenine nucleotide is there in one of

00:19:29 the strand in another strand there will be thymine thymine nucleotide adinine will always combine complimentarily with thymine and guanadine always combine with cytoine complimentarily the next point of this and creek model is each turn of helix is 3.4 4 nanometer. That means the complete turn one complete turn is having the length of 3 4 nanometer with 10 base pairs of the nucleotide. In this complete one turn there are 10 base pairs and the distance between two base pairs. Here you can see the distance between two base pair is

00:20:20 0.34 nanometer and the width of the DNA is 2 nanometer. Next point of this Watson and Creek model is each strand has hydrophilic deoxyibriophosph backbone on periphery and hydrophobic base strict inside means the phosphate and the sugar will be in the outer portion and the bases will be in inner side. Next feature of this model is the two strand of helix are held by hydrogen bond. Means as I told you earlier these two strands are bonded together with the hydrogen bond which is present in between the nitrogenous bases.

00:21:14 One complete turn, one complete turn of the DNA is having 10 base pairs. And the last charg rule which was given by Erin Charg in a particular DNA the concentration of adinine will always be equal to the concentration of thymine and the concentration of guanine will always be equal to cytosine. If suppose in a particular DNA fragment there are 10,000 adenine it means there will be 10,000 thymine also that is called chargap's role. Now there are some different forms of the DNA. The first form of DNA is

00:22:00 BDNA that is balanced DNA which was given by Watson and Creek which I told you in the last slide. Another DNA is ADNA that is alternate DNA. In the ADNA in one complete turn there are 11 base pairs while in BDNA there are 10 base pairs. The third form of DNA is cDNA having nine base pairs in one complete turn which is right-handed. Fourth form of DNA is DDNA having eight base pairs in one complete turn. And the last form of DNA is Z DNA zigzag DNA having 12 base pair in one complete turn. These are the four different types

00:22:49 of sorry five different types of DNA forms. Now let's see the different functions performed by the DNA. First DNA carries hereditary information. What is the meaning of heredatory information? The thing the molecule which get transformed from one generation to another is DNA. But what is there in the DNA which exactly is having the information related to living organism and that information is nothing that is the codes which synthesizes the protein and protein actually perform the various function in the

00:23:39 cells. The next function of DNA is it control various types of metabolic activities of the cells. Whenever cells has to undergo catabolic reaction the DNA will give the direction and whenever the cell has to go in anabolic reaction the DNA will give the direction and accordingly the DNA per the cells perform the different functions. The next function of DNA it enables cells to maintain grow and divide the growth and the division of the cells are under the control of the DNA. Next is DNA contribute to variation by

00:24:20 undergoing mutation. As you as we can see no one is similar in the phenotypic phenotypically we are not very much similar and that's because of the variation in the DNA. That's because of the mutation in the DNA. The next function of the DNA it brings about differentiation of cell. Differentiation of cells is different from division. Division means a cell divide to form similar type of cells. But in differentiation the cells divide to form different type of cells. They are not similar as that of the parental cell. So

00:25:03 these are the few function of the DNA. Now here are some differences between DNA and RNA with four types of nitrogenous bases. Cytosine, guanine, adenine and uricil. Thymine is not there in RNA. And in DNA, DNA is double stranded. They have cyc cytosine, guanine, adinine and thymine bases. So if you can see RNA is single stranded and DNA is double stranded. RNA is having a U CG as nitrogenous base and DNA is having a TCG as nitrogenous base. Here are some more differences. As I already told you in

00:25:58 the last slides, RN is having ribos sugar that's why RNA is called ribboucleic acid and DNA is having deoxyibbou that's why DNA is called deoxxyribboucleic acid. Adenine pairs with uricil. In case of transfer RNA and in case of DNA adenine pairs with thymine regions having complimentary nucleotides pairs and form hairpin loop like a structure and helical the whole RNA is not double stranded but some of the regions have complimentary sequences that's why they form hair pin like a structure.

00:26:42 RNA is genetic material in some of the viruses while DNA is genetic material in all the living organisms except some of the viruses. If we compare the length of the DNA and RNA, the length of RNA is very much shorter as that of the DNA. So these are the some differences between RNA and DNA. Now let's answer these questions. Group the following as nitrogenous bases and nucleioides adinine, cytoine, thymine, guanosine, uricil and cytosine. You have to group them. What are the different nitrogenous bases

00:27:33 in this listed molecules? And what are the different nucleotide in this listed molecule? And answer is adinine, thymine, uricil and cytosine are the nitrogenous bases while cytoine and guanosine are nucleotide. That means there is sugar and nitrogenous base. Next question. If a double stranded DNA has 20% of cytosine, calculate the percentage of addinine in the DNA. You can use charg rule for this answer. As we know according to chargef the concentration of adinine is equal to concentration of thymine and

00:28:25 concentration of guanine is equal to concentration of cytosine. In the question we have given 20% of cytosine. It means there will be 20% of guanadine and and this makes 40% of g plus c. So remaining 60% will be a plus d and this will be equally divided. So the answer will be 30% addinine will be there in this particular DNA fragment. The next question if the sequences of one strand of DNA is this then what will be the complimentary sequence? You can use the different points given by the warsing creek that adinine always

00:29:12 combined with thymine. Thymine always combined with adenine like that guanine always combined with cyto cytosine in the complimentary. So answer is this one you can see in the slide. Next question. Which bond exist between two nucleotides and which bond exist between two strands of the DNA. When we talk about two nucleotides which form the strands of the DNA, there is phosphodiester bond in between the alcohol and the acid part of the nucleotides. And if we talk about two strands of the DNA, there is hydrogen

00:29:55 bond with in between the nitrogenous bases of two strands of the DNA. This question you can answer yourself and this I can discuss in my next session. Thank you very much. We'll meet you soon in the next session. [Music]