one of the topics that are commonly taught in a biochemistry course are nucleic acids now you might be wondering what exactly are nucleic acids and there are two forms of nucleic acids i'm sure you heard of them dna and rna dna stands for deoxyribonucleic acid rna is simply ribonucleic acid but both of these are different types of nucleic acids as you can see dna is a double-stranded nucleic acid it forms an alpha helix whereas rna is a single stranded nucleic acid so that's one difference between the two there are other differences now dna is mostly located in the nucleus particularly in eukaryotes whereas rna you could find it outside of the nucleus and dna basically its function is to store the genetic information it serves as the library of the cell whereas rna it can be used to transfer genetic information from one part of the cell to another and it can also be used to synthesize protein there's different types of rna you have ribosomal rna transfer rna and messenger rna so if you see trna that's transfer rna if you see mrna that's messenger rna and then rrna is ribosomal rna dna and rna are both polymers now you might be wondering what exactly is a polymer a polymer is basically a long molecule made up of tiny units called monomers and the monomers that make up dna and rna are known as nucleotides now there's different types of nucleotides but they all have three basic parts to it so each nucleotide has a pentose sugar a five carbon sugar a nitrogenous base and a phosphate group so p stands for phosphate s is for sugar b is for base now in dna the type of sugar that we have is a five carbon sugar known as deoxyribose now i'm going to compare it to rna so you can see the difference rna has a ribose sugar instead of a deoxyribose sugar it still has a nitrogenous base and it has a phosphate group but the difference is an extra hydroxyl group now let's go ahead and number the carbons on the ribose sugar this is carbon 1 that's where the nitrogenous base is attached to carbon 2 3 4 and carbon 5 is outside of the pentose ring and that's where the phosphate group is attached to so in dna notice that we don't have a hydroxyl group on carbon 2 and so that is why it's called deoxyribose it's a deoxyribose sugar because it's lacking in oxygen whereas in rna you have a ribose sugar that's why rnase is called ribonucleic acid but dna is called deoxyribonucleic acid but besides that they both have a phosphate group and a nitrogenous base now let's focus on the nitrogenous bases found in dna and in rna so dna contains the bases adenine guanine cytosine and thymine in rna the bases are adenine guanine cytosine but instead of thymine it's uracil and so that's another difference between rna and dna it's a typical test question so make sure you're aware of that difference so uracil is found in rna and thymine is found in dna now the nitrogenous bases that we've been talking about can be divided into these two categories purines and pyrimidines now the purines contain two rings one of the ring is basically a six membered ring and the other one is a five-membered ring pyrimidines on the other hand contain only one ring and it's a six membered ring now the purines they need to be aware of are adenine and guanine the pyrimidines include cytosine thymine and uracil now let's talk about drawing these structures and also how to number them for some of you you may need to be able to draw these structures on your tests and for those of you who don't need to memorize it you can fast forward this section or you can sit back relax grab a bag of popcorn and just enjoy the show so let's start with the purines on the left side i'm going to draw adenine and on the right side i'm going to draw guanine now in the first ring they both contain two nitrogen atoms and four carbon atoms in the second ring they also contain two nitrogen atoms so both adenine and guanine has that uh that same structure so if you start with the base structure it can help you to remember how to draw these two purines now both adenine and guanine they have a double bond in the middle and they have another double bond in this position and here as well now let's talk about where they're different by the way there's a hydrogen here so that's an h if you don't see a hydrogen that means that there's a lone pair on the nitrogen now adenine has an nh2 group on this position right here so that's where it's different relative to guanine guanine has an nh2 group towards the right and at the same time it has a carbonyl group in this location so if you remember that it can help you to draw these two structures so that's the difference between adenine and guanine now let's talk about numbering the rings so this nitrogen represents number one and then you need to count it in a counterclockwise direction so this is two three four five six then you move on to the five member ring this is seven and we're going to count it in a clockwise direction so this is eight and this is nine now what you need to know with purines is that when you attach them to a ribose they will be connected let me draw a ribose ring i'm just going to draw a box to represent the ribose just to keep it simple but what i want you to take from this is that the ribose ring is attached to the nitrogenous base at position 9 when dealing with purines the permanent is different but for purines the ribose is attached to the n9 position so it's the ninth position on a nitrogen atom on a purine ring so you may need to know that for a test maybe not it depends on if the teacher is going to quiz you on that fact i don't know now let's move on to the pyrimidines so there's three structures that we need to draw now let's start with the first one so once again we're gonna have a six membered ring with two nitrogen atoms and four carbon atoms just like we had in the case of the purines we only have a six membered ring here but we're not going to have the five-member ring for the pyrimidines but the structure of the membered ring is very similar so on the left i'm going to draw let's start with thymine and then in the middle i'm going to draw uracil and then cytosine so all three of these nitrogenous bases they have the same general structure the six-membered ring as you can see it's very similar now let's talk about the way we're going to count it so this is going to be number one and we're going to count it in a clockwise direction so this is two three four five and six now the ribose will be attached to the nitrogenous base at the n1 position so make sure you uh keep that in mind if you're taking notes i'm gonna get rid of the numbers but you can add it in your notes so this is going to be a hydrogen in the case of thymine and we're going to have a double bond between positions five and six and the same is true for the rest of them now for thymine we have a carbonyl group at position four and another carbonyl group at carbon two and here we have a hydrogen so that's thymine now uracil looks very similar to thymine with one key difference thymine has a methyl group but your cell does not and so that's the difference between thymine and uracil your cell has a hydrogen if you don't see it it's an invisible hydrogen but it's there now in the case of cytosine we have a carbonyl group on carbon 2 just like thymine and uracil so they're similar in that respect however we do have something different in cytosine and that is we have an nh2 group on carbon four and so that's how cytosine differs from thymine and uracil it has this nh2 group in this position in addition to that it also has a double bond between positions three and four so those are the three pyrimidines that you may need to know and just remember uracil is found only in rna thymine is found only in dna and cytosine is found in both dna and rna now here's a question for you what is the difference between a nucleotide and a nucleoside what would you say perhaps you heard of the word nucleoside what really is a nucleoside well let's go back to nucleotides we know that a nucleotide has three parts as mentioned before it has a ribose or a deoxyribose sugar it has a nitrogenous base which could be a pyrimidine with one ring or a purine with two rings and it also has a phosphate group now in the case of a nucleoside it doesn't have three parts a nucleoside has two parts it has the five carbon sugar and it has the nitrogenous base it does not have the phosphate group so this is a nucleoside it's the sugar and the nitrogenous base but once you add the phosphate group to a nucleoside then it becomes a nucleotide so make sure you understand the difference and also the name in so let's say this is cytosine which is one of the three pyrimidines we talked about now by itself cytosine is a nitrogenous base now let's focus on the nomenclature so this is cytosine when you add the ribose sugar to it it becomes the nucleoside and it's called citidene in the case of rna but in the case of dna it's deoxycitine and it really depends on the presence of the oh group on carbon 2. so this is one two three four five there's always going to be an o h group on carbon three but if we don't have an o h group on carbon two it's called deoxycitadine if we do have it then it's called acidine now let's think about this if the nitrogenous base is called cytosine and if the nucleoside is called citadine what is the name of the nucleotide that contains the cytosine nitrogenous base so it's going to sound weird but it's called citadelate chances are you probably don't need to know that for your tests but for those of you who may need to know it that's what the nucleotide is called so when you hear the word cytosine it's not referring to this entire nucleotide but rather just the base that's in the nucleotide but if you hear acetylate that's the entire nucleotide so here is a summary that can help you with the nomenclature of nucleosides and nucleotides on the left we have the nitrogenous base adenine once we add a ribose sugar to it it becomes adenosine and then if we add the phosphate group it becomes added excuse me wow i said that wrong adenylate looking at guanine the situation is similar as a nucleoside it's guanosine and as a nucleotide with the phosphate group guanolate now the nitrogenous base thymine once we add a ribose sugar to it it becomes thymidine or thymidine if that's how you say it but since thymine is found in dna chances are it's going to be added to a deoxyribose sugar and so it becomes deoxytimidine and instead of thymodylate it becomes deoxy feminically in dna my pronunciation of these names may not be the best so don't quote me on that you can look it up yourself but these are the names that corresponds to the nitrogenous base the nucleus sides and the nucleotides now let's talk about namin nucleosides how would you name this particular nucleoside so the first thing we need to do is identify the type of nitrogenous base that we have now based on the structures that we drew earlier what kind of base do we have well first is it a purine or is it a pyrimidine now if you recall pyrimidines are nitrogenous bases that have only one ring so because this is a two ring nitrogenous base we have a purine now there's two parents you need to be familiar with and that's adenine and guanine so which one is this is this adenine or guanine so this particular nitrogenous base is called guanine now what does it become once we add a sugar to it guanine plus the ribose sugar becomes the nucleoside guanosine and so that's what we have here this is position one two three four five six seven eight nine so as we can see the purine is attached to the ribose at the knife position on the nitrogen atom now what happens to the name if we put let's say a methyl group on carbon 8 how do we name this particular nucleoside well this becomes eight methyl guanosine now what if we remove a hydroxyl group let's say if we replace this with a hydrogen as in the case of dna what does it become now so now we have a deoxyribose and so this is going to become deoxyguanosine this is carbon 1 on the ribose sugar this is 2 3 4 and this is carbon 5. so now the way we're going to name it i'm running out of space here so let's see if i can fit in it's going to be 8-methyl dash 2-deoxy guanosine because we don't have the oxygen or the hydroxyl group rather on carbon 2 of the rival sugar so now it's deoxy guanosine and so that's a simple example of how you can name a nucleoside with a purine ring let's try another example so how can we name this particular nucleoside so first let's start with the nitrogenous base now we have a one ring nitrogenous base so that means it's a pyrimidine and we have three options it's either cytosine thymine or uracil now looking at the nh2 at the top only one of those three pyrimidines have the nh2 on the top and if you remember this is the nitrogenous base cytosine now combined with the ribose sugar it becomes the nucleoside called citadine and so that's the name of this particular nucleoside now how will the name change if we add a methyl group to that carbon so we need to number it this is one two three four five six so this becomes six methyl citadine and so that's how we can name it and also remember that the ribose is attached to the pyrimidine ring at the n1 position for the purine it was the n9 position so just keep that in mind now let's shift our focus to name in nucleotides so we're going to have our ribo sugar our nitrogenous base and a phosphate group so how can we name this particular nucleotide so the nitrogen is base that we have this is g and so that's guanine when we combine it with the sugar it becomes a nucleoside called guanosine but now how do we name it once we have the phosphate group so it becomes guanolate when the phosphate group is at position five another way in which we can name this particular nucleotide is we can start with the name of the nucleoside guanosine and then specify the location of the phosphate so we could say guanosine dash five dash monophosphate because we have one phosphate attached to the ribose sugar and so that's how we can name this particular nucleotide now let's try another example so this time the nitrogenous base that we're going to use is adenine and the phosphate group is going to be placed in a different position so you can also see phosphate represented this way so how can we name this particular nucleotide so given the base adenine once we combine it with the sugar it becomes the nucleoside adenosine now the phosphate group is located on carbon 3 of the ribose ring so to put it together we're going to start with the name of the nucleoside adenosine and then specify the location of the phosphate group so adenosine dastery dash mono phosphate and so that's how we can name that particular nucleotide now let's try another example so we're going to use the same nitrogen is base adenosine but this time we're going to have multiple phosphate groups so let's say if we have three of them how do we name it now so we're going to start by naming the nucleoside so if we combine the ribose sugar and the nitrogenous base that is called adenosine now we have three phosphate groups and so it's going to be called triphosphate trifi3 and it's located on carbon 5. so it's adenosine dash 5 that's triphosphate now this particular nucleotide has a common name and so sometimes the 5 is just ignored because it's a very common molecule and so it's simply referred to as adenosine triphosphate and perhaps you heard of it as this molecule atp so that's adenosine triphosphate now there's some other ones for instance if you hear the word adp it stands for adenosine diphosphate so instead of having just one phosphate group or three now you have two phosphate groups so that's adenosine diphosphate and if you hear the abbreviation amp this is adenosine monophosphate so there's just one phosphate group instead of two or three so what i'm going to do at this point is draw a representation of a dna strand so here we have our sugar attached to a phosphate group and then this is going to be attached to a nitrogenous base so let's put cytosine in it and over here it's going to be attached to another phosphate group and then that's going to be attached to another ribose sugar actually deoxyribose since we're dealing with dna and so this is going to be adenine this time and then we're going to have another phosphate group and let's put thymine in this box now at this point go ahead and draw the complementary strand on the right side using the left side as a starting point so first let's draw the nitrogenous bases that will pair up with c a and c and then attached to each nitrogenous base we have the sugar but notice the direction of the sugar how it's like pointed up for the complementary strand it's going to be pointed down so we're going to draw it this way and then we're going to have a phosphate group attached to it and here we have another phosphate group and then another sugar unit we're going to talk about the connectivity of the phosphate group shortly i just want to complete this first so what bases will go in these boxes now what you need to know is that c cytosine will always pair up with g guanine so we need to put g inside this box adenine a will always pair up with thymine and dna and t will pair up with a now the next thing you need to put are the hydrogen bonds located between these base pairs and so it's the hydrogen bonds that keep the two strands in dna attached to each other so there's three hydrogen bonds connecting c and g now between a and t there are two hydrogen bonds holding them together now if you recall from chemistry hydrogen bonds exists whenever hydrogen is attached to elements such as oxygen nitrogen or fluorine and an h bond is basically an intermolecular force that exists between separate molecules now for those of you who may want to review on that um if you do a youtube search type in intermolecular forces organic chemistry tutor you should see a video that will give you a review on intermolecular forces and dipole interactions and things like that now on the left side and also on the right side this is known as the sugar phosphate backbone and it makes sense you have your phosphate groups on the left attached to the sugar units now on the sugar this is carbon one two three four and 5. so notice that the phosphate group is attached to carbon 3 and carbon 5 of the sugar units and so this is called a 3 five phosphodiester linkage and it's a covalent linkage a covalent bond is whenever two atoms are connected to each other by means of sharing electrons so whenever two elements or two atoms come together by sharing electrons they form a covalent bond now the next thing i want to mention is that these two strands these complementary strands they are anti-parallel to each other so the strand on the left it runs in the five to three direction now the strand on the right it goes in the opposite direction so if we focus on the top sugar unit this is carbon 1 2 3 4 5. so notice that it's going in the five to three direction but any other way so thus these two strands are anti-parallel they run in opposite directions and so these are some basic things that you need to know if you have a test coming up you never know which one of these facts you might be tested on so just make sure you know that stuff now i have one more question for you consider this particular strand of dna write the sequence for the complementary strand feel free to pause the video and try it complementary to 5 is 3 and you need to know that a pairs up with t and c pairs up with g so here we have a we're going to pair it up with thymine and here we have t and let's pair it up with adenine and c we're going to pair it up with guanine and a is going to go with t g we're going to pair it up with c and so forth so this is the complementary strand that's how you can write the sequence by knowing this piece of information well that's basically it for this video hopefully you found it to be helpful and if you want more videos like this feel free to subscribe and don't forget to click the notification bell so you can receive updates on any videos i'm going to post in the future thanks again for watching