Youtor
Introduction to nucleic acids
>> YOUR LINK HERE: ___ http://youtube.com/watch?v=lqeVl3H5mzI
See full presentation with speaker notes at: • https://docs.google.com/presentation/... • SCRIPT: • Alright so today we’re going to briefly talk about nucleic acids, a class of biomolecules that includes DNA and RNA. We’re going to touch on what DNA is made of as well as some related enzymes that affect DNA at the molecular level. • To start off, I think this quote here best sums up the importance of nucleic acids, since they really are essential to life as we know it. • We have here a spinning image of the characteristic double helix structure of DNA, and we’ll be talking about how this structure is assembled and broken down in all living things. • But first, we need to understand the smaller parts that make up this structure. These are the blue parts that you’re seeing toward the center of this helix. I’m of course talking about nucleotides • So, the individual units that make up DNA and RNA are called nucleotides, and these structures can be broken down into even smaller units, since they have a phosphate group, a sugar ring, and a nitrogenous base. This sugar and phosphate group, this one and this one, make up the outer parts of DNA, which is often called the sugar-phosphate BACKBONE of DNA. The nitrogenous bases here make up the interior of DNA. • DNA is coded into the different kinds of nitrogenous bases we see at this level. Five major nitrogenous bases are listed on the right here. If we want to see what a nucleotide looks like with each of these nitrogenous bases, we just have to place them in place of this base here, so let’s try that. • Now we have five nucleotides based on the five nitrogenous bases we have listed on the right. These bases can be broken down into two groups. We have the pyrimidines, which are the nucleotides with nitrogenous bases with one ring structure. And we have the purines, which have two ring structures. Again, purines, like guanine or adenine, have double ring structures, while the pyrimidines, like cytosine, uracil, and thymine have two rings. • There are a couple mnemonics for remembering these purine and pyrimidine categories. For purines, we say they are PURE AS GOLD, where the Pu comes from purine, the A in AS for adenine, and the G in gold for Guanine. For pyrimidines, we say CUT THE PYE, where the C-U-T in cut is all three pyrimidines, and the misspelling of pye is for the P-Y in pyrimidines. • Now let’s eliminate all those words and keep the four nucleotides that are present in DNA. These top four on the right, cytosine, guanine, adenine, and thymine are the ones in DNA. That’s CGA and T. In RNA, we replace the thymine with uracil, but what we’re looking at now is the four nucleotides that are in DNA. • So, we’re going to flip two of them to see how they bind to each other. Sooooo flip • And let’s rotate them a bit... • and we can draw dotted lines that represent the bonds between these nucleotides. This kind of chemical bond is called a hydrogen bond, and this is what is holding double helix of DNA together. To summarize this these bonds, we have that guanine binds to cytosine with three hydrogen bonds up here. And on the bottom, adenine binds to thymine with two hydrogen bonds. • These pairs, the G with the C up top and the A and the T below, are called complementary base pairs. These pairs are important because they allow for genetic material to be duplicated with high accuracy. The affinity between the G and the C is different enough from that of the A and T that these molecules will always want to hydrogen bond in these pairs. And these hydrogen bonds are strong enough to hold DNA together. • Now imagine if we took many of these pairs and stacked them on top of each other, we might get a shape that looks like THIS • We can see how this stack becomes larger and starts looking like a ladder. • It’s important to notice here that we have two strands of DNA that are joined by hydrogen bonds. This “ladder” of DNA has a constant diameter. We see the sugar-phosphate backbone that makes up the outside of DNA. And we also see the nitrogenous bases that make up the rungs of the “ladder”. • Another thing to add here is the concept of DNA being antiparallel. A strand of DNA can be oriented according to the number of the carbon in the ribose sugar that binds to the adjacent phosphate. This allows us to designate a 5’ end and a 3’ end to each DNA strand, based on the 5’ and 3’ ribose carbons in the backbone. The concept of antiparallelism means that these two strands or DNA are oriented such that they are opposite to each other. It might be easier to see this idea of antiparallelism if we use arrows, as shown here. • ... • SEE REST OF SCRIPT AT ABOVE LINK • I created this presentation with Google Slides. • Image were created or taken from Wikimedia Commons • I created this video with the YouTube Video Editor.
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