So now that we know that one of the components of a single nucleotide monomer is the Nitrogenous Base, in this video, we're going to focus on the 5 Nitrogenous Bases. And so once again there are 5 different Nitrogenous Bases and these 5 nitrogenous bases can be grouped together as either pyrimidines or as purines. The pyrimidines are single-ringed molecules, whereas the purines are double-ringed molecules. If we take a look at our image down below on the left-hand side, notice that we're showing you the nitrogenous bases, which can once again be grouped into these two groups, the pyrimidines, which we have over here on the left-hand side, and the purines, which we have over here on the right-hand side. And notice that the pyrimidines, as we mentioned above, are all single-ringed molecules, so they only have one single ring, whereas the purines over here are all double-ringed molecules, so they all have 2 rings like what we see here. These are called nitrogenous bases for a reason because they have plenty of nitrogen atoms, as you can see, what I'm highlighting right here. All of these nitrogen atoms make these bases pretty nitrogenous, and that's why we call them nitrogenous bases. It's also important to note, that each of these nitrogenous bases has a name, and so you can see we have cytosine, thymine, and uracil are the pyrimidines, And then we have Adenine and Guanine as the purines. Each of these nitrogenous bases' names has a unique first letter. For instance, cytosine's first letter is unique. It's the only one that starts with a 'c' and so we can use the first letter 'c' to abbreviate cytosine. Thymine's unique first letter is 't', uracil's unique first letter is 'u', adenine's unique first letter is 'a', and guanine's unique first letter is 'g'. We can abbreviate these nitrogenous bases just by using one letter. Notice that when we introduced pyrimidines up above that we made the 'y' here in pyrimidines interactive for you guys to fill out yourselves as you watch this video. The reason that we're emphasizing this 'y' here is because notice that most of the pyrimidines, which have a 'y' in them, also have a 'y' in themselves. So, cytosine and thymine have 'y's in them, which make them pyrimidines. Notice that the purines, such as adenine and guanine, do not have a 'y' in them and so, they're going to be batched over here. The only exception to this 'y' is going to be uracil. Uracil is a pyrimidine even though it doesn't have a 'y'. But if you can just remember this one exception, then that'll help you batch these nitrogenous bases into the correct groups. What you'll also notice is down below the image, we have these memory tools to also help you group and batch these nitrogenous bases. So when you think of pyrimidines, that kind of sounds like pyramids. And when you think about pyramids, you think about the Egyptian pyramids. And of course, we all know that underneath the Egyptian pyramids there are creepy tombs under those pyramids. Here we have an image of the creepy tombs under the Egyptian pyramids. You can think that the 'c' in creepy is for the 'c' inside cytosine, the 't' in tombs is for the 't' in thymine, and the 'u' in under is for the 'u' in uracil. By remembering pyrimidines, thinking about pyramids, you'll think about the creepy tombs under the pyramids and you'll be able to group these nitrogenous bases no problem. On the other hand, the purines, all you got to do is think about pure as gold. Here we got this guy. He's got some gold in his hand, and he's thinking pure as gold. What you can see here is that the 'a' in 'as' is for the 'a' in adenine, and the 'g' in gold here is for the 'g' in guanine. By remembering that purines are pure as gold, you'll be able to determine these, adenine and guanine are purines no problem. Another important thing to note here is that thymine is a nitrogenous base that is uniquely found only in DNA, whereas uracil, on the other hand, is a nitrogenous base that is uniquely found only in RNA. In RNA structure, what we'll see is that all of the 't's are going to be replaced with 'u's. 'U's, once again, are specific for only in RNA, whereas 't's are specific for only in DNA. So that's an easy way for us to be able to identify if a strand is DNA or RNA just by looking to see if 't's or 'u's are being used. This leads us to talk a little about DNA structure here because, in DNA structure, the nitrogenous bases on different DNA strands are going to base pair together. The base pairing works in this fashion where adenines or 'a's are always going to pair with thymines or 't's, and cytosines or 'c's are always going to pair with guanines or 'g's. A purine is always going to be paired up with a pyrimidine. 'a's pair with 't's. Once again, the pyrimidine of cytosine is always going to be paired up with a purine of guanine. They always pair up pyrimidine with a purine. If we take a look at the image over here on the right-hand side, notice that it's focusing in on DNA base pairing. DNA is made up of 2 strands. What you'll see is that there's one strand over here on the left and there's another strand over here on the right. These two strands connect to each other via interactions between the base pairs, where once again 'a' always pairs with 't' and 'c' always pair with 'g'. Notice that the 'a' over here on this strand is always going to pair with 't's on this strand and vice versa, And the 'c's on this strand are always going to pair with the 'g's on this strand over here and vice versa. Once again, adenines will always pair with thymines, and cytosines will always pair with guanines and so this is really important to note here. This here really concludes our introduction to the 5 nitrogenous bases and we'll be able to get some game practicing applying these concepts as we move forward. I'll see you all in our next video.